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The primary objective was to examine the utility of a novel method of detecting "actual" kinematic changes using the within-subject variation. Twenty firefighters were assigned to one of two groups (lifting or firefighting). Participants performed 25 repetitions of two lifting or firefighting tasks, in three sessions. The magnitude and within-subject variation of several discrete kinematic measures were computed. Sequential averages of each variable were used to derive a cubic, quadratic and linear regression equation. The efficacy of each equation was examined by contrasting participants' sequential means to their 25-trial mean±1SD and 2SD. The magnitude and within-subject variation of each dependent measure was repeatable for all tasks; however, each participant did not exhibit the same movement patterns as the group. The number of instances across all variables, tasks and testing sessions whereby the 25-trial mean±1SD was contained within the boundaries established by the regression equations increased as the aggregate scores included more trials. Each equation achieved success in at least 88% of all instances when three trials were included in the sequential mean (95% with five trials). The within-subject variation may offer a means to examine participant-specific changes without having to collect a large number of trials., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Although core stiffness enhances athletic performance traits, controversy exists regarding the effectiveness of isometric vs. dynamic core training methods. This study aimed to determine whether long-term changes in stiffness can be trained, and if so, what is the most effective method. Twenty-four healthy male subjects (23 ± 3 years; 1.8 ± 0.06 m; 77.5 ± 10.8 kg) were recruited for passive and active stiffness measurements before and after a 6-week core training intervention. Twelve subjects (22 ± 2 years; 1.8 ± 0.08 m; 78.3 ± 12.3 kg) were considered naive to physical and core exercise. The other 12 subjects (24 ± 3 years; 1.8 ± 0.05 m; 76.8 ± 9.7 kg) were Muay Thai athletes (savvy). A repeated-measures design compared core training methods (isometric vs. dynamic, with a control group) and subject training experience (naive vs. savvy) before and after a 6-week training period. Passive stiffness was assessed on a "frictionless" bending apparatus and active stiffness assessed through a quick release mechanism. Passive stiffness increased after the isometric training protocol. Dynamic training produced a smaller effect, and as expected, there was no change in the control group. Active stiffness did not change in any group. Comparisons between subject and training groups did not reveal any interactions. Thus, an isometric training approach was superior in terms of enhancing core stiffness. This is important since increased core stiffness enhances load bearing ability, arrests painful vertebral micromovements, and enhances ballistic distal limb movement. This may explain the efficacy reported for back and knee injury reduction.

Novel ideas for core endurance training are continually being created. However, studies of their mechanism of action assist in evaluation of their potential as a training tool, for a variety of people and purposes. The specific purpose of this study was to evaluate a weighted hula hooping training program for its efficacy on improving core muscular endurance and influence on measures of body composition. Eighteen women participated in a weighted hula hooping trial lasting 6 weeks, although only 13 returned for posttrial re-assessment. Hip and waist circumferences, 5 torso muscle endurance tests, and 5 skinfold measurements ("sum of 5") were measured before and after the exercise program. Paired samples t-tests were performed to examine pre/post changes. On average, participants experienced a significant decrease in waist and hip circumference -3.4 cm (p < 0.01) and -1.4 cm (p ≤ 0.05), respectively and waist-to-hip ratio from 89.3 cm down to 87.3 cm (t = 3.312, p < 0.01). There were no significant changes in torso muscular endurance after the 6 weeks of hooping; however, the average "sum of 5" skinfold measurements increased by 10.5 cm (p ≤ 0.05). This study of weighted hula hooping suggested that regular hooping was associated with reduced waist and hip girth together with a redistribution of body mass; however, there were no improvements in torso muscular endurance as measured by isometric testing.

The back squat is a well-researched and widely used exercise to enhance fundamental movement competency that creates a foundation for optimal mechanical strategies during a broad range of activities. The primary commentary introduced the Back Squat Assessment (BSA): a criterion based assessment of the back squat that delineates 30 potentially observable functional deficits. This follow-up commentary provides a targeted system of training cues and exercises to supplement the BSA to guide corrective intervention. We propose a criterion driven approach to corrective exercise that can support practitioners in their goal to help individuals achieve movement competency in the back squat.

Purpose: To describe female lumbar spine motion and posture characteristics during coitus and compare these characteristics across five common coital positions. Exacerbation of low back pain during coital movements and positions is a prevalent issue reported by female low back pain (LBP) patients. To address this problem, the first study to examine lumbar spine biomechanics during coitus was conducted., Methods: Ten healthy males and females performed coitus in the following pre-selected positions and variations: QUADRUPED (fQUAD1 and fQUAD2 where the female is supporting her upper body with her elbows and hands, respectively), MISSIONARY (fMISS1 and fMISS2 where the female is minimally and more flexed at the hips and knees, respectively), and SIDELYING. An electromagnetic motion capture system was used to measure three-dimensional lumbar spine angles that were normalized to maximum active range of motion-a transmitter and receiver were affixed to the skin overlying the lateral aspect of the pelvis and the spinous process of the twelfth thoracic vertebra, respectively. To determine if each coital position had distinct spine kinematic profiles (i.e., amplitude probability distribution function and total range of lumbar spine motion), separate univariate general linear models followed by Tukey's honestly significant difference post hoc analysis were used. The presentation of coital positions was randomized., Results: Female lumbar spine movement varied depending on the coital position; both variations of QUADRUPED, fQUAD1 and fQUAD2, were found to use a significantly greater range of spine motion than fMISS2 (p = 0.017 and p = 0.042, respectively). With the exception of both variations of MISSIONARY, fMISS1 and fMISS2, the majority of the range of motion used was in extension. These findings are most pertinent to patients with LBP that is exacerbated by motions or postures. Based on the spine kinematic profiles of each position, the least-to-most recommended positions for a female flexion-intolerant patient are: fMISS2, fMISS1, fQUAD1, fSIDE, and fQUAD2. These recommendations would be contraindicated for the extension-intolerant patient., Conclusions: The findings provided here may guide the clinician's specific recommendations, including alternative coital positions and/or movement patterns or suggesting a lumbar support, depending on the female LBP patient's specific motion and posture intolerances.

Background: Within the context of evaluating individuals' movement behavior it is generally assumed that the tasks chosen will predict their competency to perform activities relevant to their occupation., Objective: This study sought to examine whether a battery of general tasks could be used to predict the movement patterns employed by firefighters to perform select job-specific skills., Methods: Fifty-two firefighters performed a battery of general and occupation-specific tasks that simulated the demands of firefighting. Participants' peak lumbar spine and frontal plane knee motion were compared across tasks., Results: During 85% of all comparisons, the magnitude of spine and knee motion was greater during the general movement tasks than observed during the firefighting skills. Certain features of a worker's movement behavior may be exhibited across a range of tasks. Therefore, provided that a movement screen's tasks expose the motions of relevance for the population being tested, general evaluations could offer valuable insight into workers' movement competency or facilitate an opportunity to establish an evidence-informed intervention.

Background: Linking firefighter injury reporting to general motion patterns may provide insight into potential injury mechanisms and the development of prevention strategies., Objective: To characterize the injuries sustained by members of a large Canadian metropolitan fire department over a 5-year span., Methods: Data were taken from injury reports filed by career firefighters between 2007 and 2011. Injuries were described by job duty, type, body part affected, and the general motion pattern employed at the time of injury (e.g. lifting)., Results: Of the 1311 injuries reported, 64% were categorized as sprains and strains (musculoskeletal disorders -MSDs), the most frequent of which affected the back (32%). Categorized by job duty, 65% of MSDs were sustained while working at the fire station or during physical training-related activities. Only 15% were attributed to fireground operations. Furthermore, the associated job duty could not differentiate the types of injuries sustained; back injuries occurred primarily while lifting, knee injuries while stepping, and shoulder injuries during pushing/pulling-related activities., Conclusions: Firefighter injuries are not just a fireground problem. Injury causation may be better understood by linking the injury location and type with motion patterns rather than job duties. This information could assist in developing general prevention strategies for the fire service.

Fundamental movement competency is essential for participation in physical activity and for mitigating the risk of injury, which are both key elements of health throughout life. The squat movement pattern is arguably one of the most primal and critical fundamental movements necessary to improve sport performance, to reduce injury risk and to support lifelong physical activity. Based on current evidence, this first (1 of 2) report deconstructs the technical performance of the back squat as a foundation training exercise and presents a novel dynamic screening tool that incorporates identification techniques for functional deficits that limit squat performance and injury resilience. The follow-up report will outline targeted corrective methodology for each of the functional deficits presented in the assessment tool.

Background: Improving activity and strength of the gluteus medius muscle is a common goal among clinicians aiming to rehabilitate lower extremity and low back injuries. The functional anatomy of the hip is complex, particularly how position-dependent the activity and strength of many muscles surrounding the hip are, and the optimal exercise technique to isolate gluteus medius remains controversial. The objective of this study was to quantify the effect of altering hip orientation during side-lying clamshell and hip abduction exercises on the relative muscle activation profiles of gluteus medius and tensor fascae latae., Methods: The ratio of gluteus-medius-to-tensor-fascae-latae peak electromyography signal amplitude of 13 healthy, male participants was compared across variations of the clamshell and abduction exercises. The hip flexion angle was varied from 30°, 45°, and 60° for the clamshell, while hip rotation orientation was varied from internal, neutral, and external rotation for the abduction exercise., Findings: Varying hip angle - flexion in the clamshell exercise and internal/external rotation in the abduction exercise - did not significantly affect the interplay between gluteus medius and tensor fascae latae activation levels. Both exercises remained gluteus medius-dominant across all variations, but the gluteus-medius-to-tensor-fascae-latae ratio was far greater for the clamshell than for the abduction exercise; the clamshell may be the preferred rehabilitative exercise to prescribe when minimal tensor fascae latae muscle activation is desired by the clinician., Interpretation: These findings provide information for clinical decision-making pertaining to effective gluteus medius activation in lower extremity and low back exercise rehabilitation programs., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

This study examined pulling exercises performed on stable surfaces and unstable suspension straps. Specific questions included: which exercises challenged particular muscles, what was the magnitude of resulting spine load, and did technique coaching influence results. Fourteen males performed pulling tasks while muscle activity, external force, and 3D body segment motion were recorded. These data were processed and input to a sophisticated and anatomically detailed 3D model that used muscle activity and body segment kinematics to estimate muscle force, in this way the model was sensitive to each individual's choice of motor control for each task. Muscle forces and linked segment joint loads were used to calculate spine loads. There were gradations of muscle activity and spine load characteristics to every task. It appears that suspension straps alter muscle activity less in pulling exercises, compared to studies reporting on pushing exercises. The chin-up and pull-up exercises created the highest spine load as they required the highest muscle activation, despite the body "hanging" under tractioning gravitational load. Coaching shoulder centration through retraction increased spine loading but undoubtedly adds proximal stiffness. An exercise atlas of spine compression was constructed to help with the decision making process of exercise choice for an individual., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Study Design: Repeated measures design., Objective: To describe male spine movement and posture characteristics during coitus and compare these characteristics across 5 common coital positions., Summary of Background Data: Exacerbation of pain during coitus due to coital movements and positions is a prevalent issue reported by low back pain patients. A biomechanical analysis of spine movements and postures during coitus has never been conducted., Methods: Ten healthy males and females engaged in coitus in the following preselected positions and variations: QUADRUPED, MISSIONARY, and SIDELYING. An optoelectronic motion capture system was used to measure 3-dimensional lumbar spine angles that were normalized to upright standing. To determine whether each coital position had distinct spine kinematic profiles, separate univariate general linear models, followed by Tukey's honestly significant difference post hoc analysis were used. The presentation of coital positions was randomized., Results: Both variations of QUADRUPED, mQUAD1 and mQUAD2, were found to have a significantly higher cycle speed than mSIDE (P = 0.043 and P = 0.034, respectively), mMISS1 (P = 0.003 and P = 0.002, respectively), and mMISS2 (P = 0.001 and P < 0.001, respectively). Male lumbar spine movement varied depending on the coital position; however, across all positions, the majority of the range of motion used was in flexion. Based on range of motion, the least-to-most recommended positions for a male flexion-intolerant patient are mSIDE, mMISS2, mQUAD2, mMISS1, and mQUAD1., Conclusion: Initial recommendations-which include specific coital positions to avoid, movement strategies, and role of the partner-were developed for male patients whose low back pain is exacerbated by specific motions and postures., Level of Evidence: N/A.

The abdominal wall is a prime target for therapeutic exercises aimed to prevent and rehabilitate low back pain and to enhance performance training. This study examined the "Lewit," a corrective exercise prescribed for several purposes, which is performed lying supine in a crook-lying position and involves forceful breathing. Muscle activation and lumbar posture were compared with bracing the abdominal wall (stiffening) with robust effort and "hollowing" (attempting to draw in the wall toward the naval) with robust effort. Eight healthy male volunteers with 6 channels of electromyography were collected by means of surface electrode pairs of the rectus abdominis, external oblique, and internal oblique (IO) together with lumbar motion. The Lewit exercise caused higher muscle activity in the deeper abdominal wall muscles, in particular the IO and by default the transverse abdominis were activated at 54% maximum voluntary contractions (MVCs) on average and 84% MVC peak with no change in spine posture to maintain the elastic equilibrium of the lumbar spine. The Lewit is a deep oblique muscle activation exercise, and the activation levels are of a sufficient magnitude for training muscle engrams. This information will assist strength and conditioning coaches with program design decisions where this corrective abdominal exercise may be considered for clients who elevate the ribcage during strength exertions, or for clients targeting the deep obliques.

The impact of exercise on firefighter job performance and cardiorespiratory fitness has been studied extensively, but its effect on musculoskeletal loading remains unknown. The aim of this study was to contrast the physical fitness and low-back loading outcomes of two groups of firefighters who completed different exercise programmes. Before and after 12 weeks of exercise, subjects performed a physical fitness test battery, the Functional Movement Screen™ (FMS) and simulated job tasks during which peak L4/L5 joint compression and reaction shear forces were quantified using a dynamic biomechanical model. Subjects who exercised exhibited statistically significant improvements (p < 0.05) in body composition, cardiorespiratory fitness, muscular strength, power, endurance and flexibility, but FMS scores and occupational low-back loading measures were not consistently affected. Firefighters who are physically fit are better able to perform essential job duties and avoid cardiac events, but short-term improvements in physical fitness may not necessarily translate into reduced low-back injury risk.

Labile surfaces in the form of suspension straps are increasingly being used as a tool in resistance training programs. Pushing is a common functional activity of daily living and inherently part of a well-rounded training program. This study examined pushing exercises performed on stable surfaces and unstable suspension straps, specifically muscle activation levels and spine loads were quantified together with the influence of employing technique coaching. There were several main questions that this study sought to answer: Which exercises challenged particular muscles? What was the magnitude of the resulting spine load? How did stable and unstable surfaces differ? Did coaching influence the results? Fourteen men were recruited as part of a convenience sample (mean age, 21.1 ± 2.0 years; height, 1.77 ± 0.06 m; mean weight, 74.6 ± 7.8 kg). Data were processed and input to a sophisticated and anatomically detailed 3D model that used muscle activity and body segment kinematics to estimate muscle force-in this way, the model was sensitive to the individuals choice of motor control for each task; muscle forces and linked segment joint loads were used to calculate spine loads. Exercises were performed using stable surfaces for hand/feet contact and repeated where possible with labile suspension straps. Speed of movement was standardized across participants with the use of a metronome for each exercise. There were gradations of muscle activity and spine load characteristics to every task. In general, the instability associated with the labile exercises required greater torso muscle activity than when performed on stable surfaces. Throughout the duration of an exercise, there was a range of compression; the TRX push-up ranged from 1,653 to 2,128.14 N, whereas the standard push-up had a range from 1,233.75 to 1,530.06 N. There was no significant effect of exercise on spine compression (F(4,60) = 0.86, p = 0.495). Interestingly, a standard push-up showed significantly greater shear than TRX angle 1 (p = 0.02), angle 2 (p = 0.01), and angle 3 (p = 0.02). As with any training program for the elite or recreational athlete alike, specific exercises and programs should reflect one's injury history, capabilities, limitations, and training goals. Although none of the exercises examined here breached the NIOSH action limit for compression, those exercises that produced higher loads should be used relative to the individual. Thus, the atlas of muscle activation, compression, and shear forces provided can be used to create an appropriate program. Those individuals not able to tolerate certain loads may refer to the atlas and choose exercises that minimize load and still provide sufficient muscle activation. Conversely, an individual with a resilient back that requires an increased muscular challenge may choose exercises with higher muscle activation and spine load. This helps the individual, trainer, or coach in program design respecting individual differences and training goals.

The purpose of this study was to analyze the transference of increased passive hip range of motion (ROM) and core endurance to functional movement. Twenty-four healthy young men with limited hip mobility were randomly assigned to 4 intervention groups: group 1, stretching; group 2, stretching plus hip/spine disassociation exercises; group 3, core endurance; and group 4, control. Previous work has documented the large increase in passive ROM and core endurance that was attained over the 6-week interventions, but whether these changes transferred to functional activities was unclear. Four dynamic activities were analyzed before and after the 6-week interventions: active standing hip extension, lunge, a standing twist/reach maneuver, and exercising on an elliptical trainer. A Vicon motion capture system collected body segment kinematics, with hip and lumbar spine angles subsequently calculated in Visual 3D. Repeated measures analyses of variance determined group effects on various hip and spine angles, with paired t-tests on specific pre/post pairs. Despite the large increases in passive hip ROM, there was no evidence of increased hip ROM used during functional movement testing. Similarly, the only significant change in lumbar motion was a reduction in lumbar rotation during the active hip extension maneuver (p < 0.05). These results indicate that changes in passive ROM or core endurance do not automatically transfer to changes in functional movement patterns. This implies that training and rehabilitation programs may benefit from an additional focus on 'grooving' new motor patterns if newfound movement range is to be used.

Repeated flexion and extension of an intervertebral disc has been shown to affect the angular stiffness of spinal motion segments and is a barometer of the mechanical integrity of the disc. A degenerated disc that loses height causes higher levels of stress on the annulus and facet joints which may increase its level of degeneration; restoring disc height may therefore help to slow this degenerative cascade. Previous research has indicated that nucleus implants have the potential to improve the mechanical characteristics of a disc and an implant that is custom-fit to the intervertebral disc yields the best results with respect to decreasing annular degeneration. Two groups of porcine spinal motion segments were exposed to repeated flexion and extension. One group was then injected with a novel hydrogel while the other group was used as a control. Both groups were then exposed to another round of cyclic flexion and extension to examine the effect that the hydrogel had on restoring the original mechanics to the motion segments. Angular stiffness was restored to the group which received the hydrogel injection in addition to a significant improvement in specimen height. No significant changes were seen in the group which did not receive an injection. It would appear that use of the novel injectable hydrogel is able to restore angular stiffness to cyclically fatigued spinal motion segments. It is also important to note that continued repetition of the event causing specimen fatigue after performing hydrogel injection will result in an eventual return to the same fatigued state.

Background: In this case report an incumbent firefighter partially ruptured his right Achilles tendon during a study of the physical demands of firefighting., Methods: Kinematics and kinetics of the lower limbs and trunk were collected while the firefighter performed two simulated fire ground tasks. From this unexpected event, two insights were obtained that should be considered in all future injury prevention and reporting efforts., Findings: (i) Consider the full anatomical linkage--the right ankle and knee kinematics leading up to the onset of injury trial were comparable to all preceding repetitions. However, there was a notable difference in the left knee starting position before the initiation of movement of the 37th hose-advance trial. (ii) Consider the cumulative load--the task in question comprised forward and backward phases. A marked difference was observed in the frontal-plane ankle moment during the return phase of the trial preceding the injury. Additionally, the magnitude of the left side vertical ground reaction force was comparable across all trials, suggesting that loads experienced by the right limb were also similar. This would indicate that the tolerance of the Achilles tendon and not the magnitude of the loading was altered., Interpretation: The unfortunate injury captured in this work provides insight into the complexity of characterizing the pathways of injury. It is recommended that future injury prevention and reporting efforts consider individuals' physical demands (at work and in life) and document the nature of loading (i.e., frequency, duration, magnitude, type) when considering the mechanism for injury., (Crown Copyright © 2013. Published by Elsevier Ltd. All rights reserved.)

This study investigates the consequences of carrying load in one hand versus both hands. Six participants walked carrying buckets containing various weights. The weight was either carried in one hand or distributed evenly between both hands. Electromyography, force plate and body kinematic data were input to a three-dimensional anatomically detailed model of the spine to calculate spine loading. Carrying loads in one hand resulted in more load on the low back than when the load was split between both hands. When carrying 30 kg in one hand, the low back compression exceeded 2800 N; however, splitting the load between hands reduced low back compression to 1570 N (reduction of 44%). Doubling the total load by carrying 30 kg in each hand actually produced lower spine compression than when carrying 30 kg in one hand. Balancing the load between both hands when carrying material has merit and should be considered when designing work., Practitioner Summary: Carrying a load in one hand (30 kg) resulted in more spine load than splitting the same load between both hands (15 kg). When carrying double the load in both hands (30 kg in each hand vs. 30 kg in one hand), spine load decreased, suggesting merit in balancing load when designing work.

Objective: To establish torso muscle endurance values in children aged 7 to 14 years, as well as ratios between torso extensors, flexors, and lateral torso flexors, with applications in clinical assessment, rehabilitation, physical education targets, and athletic training program designs. It was hypothesized that boys and girls mature differently in terms of torso muscle endurance., Design: Measurements of torso muscle endurance were performed by using 4 tests in healthy children., Setting: Elementary school in Novi Sad, Province of Vojvodina, Republic of Serbia., Participants: Children from 1 elementary school (N=753, n=394 boys and n=359 girls) were grouped into 8 age strata., Interventions: Not applicable., Main Outcome Measures: Four tests established isometric physical endurance: Biering-Sørensen test for extensor endurance, flexor endurance test, and right- and left-side bridge tests. The mean, ratio, standard deviation, and 25th, 50th, and 75th percentile scores were determined for each sex/age stratum., Results: A 2-way analysis of variance indicated that girls had higher mean endurance times for torso extension and torso flexion than did boys. For example, times measured by using Biering-Sørensen and right-side bridge tests were significantly greater for girls than for boys across all age groups (P<.023). Boys can sustain the side torso test longer than can girls. Furthermore, 3-dimensional torso muscle endurance is under significant impact of age. Tukey Honestly Significant Difference post hoc tests confirmed that within and between sex exist significant differences in mean endurance times in all age strata at the significance level P=.05., Conclusion: Both age and sex influence differences in torso endurance in children aged 7 to 14 years. These data of endurance times, their ratios, and percentiles in healthy subjects form a database that may be useful for providing training and rehabilitation targets., (Copyright © 2012 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.)

Background: A critical issue for constructing a progressive rehabilitation program is the knowledge of muscle activation levels across exercises and within exercise modifications. Many exercises are offered to enhance gluteal muscle activation during functional rehabilitation but little data exists to guide the progression of exercise intensity during rehabilitation. The objective of this paper was to examine the effects of altering resistance band placement during 'Monster Walks' and 'Sumo Walks.', Methods: Nine healthy male volunteers formed a convenience sample. Sixteen electromyography channels measured neural drive of selected muscles of the right hip and torso muscles. Three resistance band placements (around the knees, ankles and feet) during the two exercises were utilized to provide a progressive resistance to the gluteal muscles while repeated measures ANOVA with Bonferroni adjustment was used to assess differences in mean EMG. The presentation of exercises and band placement were randomized., Findings: Examining muscle activation profiles in the three hip muscles of interest revealed the progressive nature of the neural drive when altering band placement. Tensor fascia latae (TFL) demonstrated a progressive activation moving the band from the knee to the distal band placement, but not between the ankle and foot placements. Gluteus medius demonstrated a progressive activation moving distally between band placements. Gluteus maximus was preferentially activated only during the foot placement., Interpretation: The band placements offered a progressive increase in resistance for hip rehabilitation, specifically the gluteal muscles. The added benefit of placing the band around the forefoot was selective enhancement of the gluteal muscles versus TFL presumably by adding an external rotation effort to the hips. This information may assist those who address gluteal activation patterns for patients suffering hip and back conditions where gluteal activation has been affected., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: The elliptical trainer is a popular exercise modality, yet its effect on the lumbar spine is poorly understood. The purpose of this study was to analyze the effect of different hand positions, speed and stride lengths on spine kinematics and corresponding muscle activity while using the elliptical trainer, and compare with those demonstrated in normal walking., Methods: Electromyographic data was collected over 16 trunk and gluteal muscle sites on 40 healthy males (mean age (SD)=23(3)) while on the elliptical trainer. Two stride lengths (46, 66cm), 2 speeds (self-selected, 30% faster), and 3 hand positions (freehand, central bar, handles) were analyzed. Lumbar spine kinematics was calculated from data collected using a motion capture system. Results were compared to those found in walking using repeated measures ANOVA for each dependent variable with Bonferroni adjustments (P<0.004. Correlations were made between lumbar motion and various anthropometric measures., Findings: All significance levels comparing walking to elliptical varied according to stride length, speed and hand position. Average lumbar flexion angles and lumbar rotation were generally greater on the elliptical trainer, whereas walking produced more frontal motion. Total lumbar flexion/extension was similar between the two activities. Muscle activation patterns of the gluteal muscles were consistently higher on the elliptical, whereas the back extensors, latissimi and internal obliques were greater in only selected conditions., Interpretation: The various hand positions, speeds and stride lengths affect lumbar motion and muscle activity on the elliptical trainer, thus must be considered when incorporated into an exercise protocol., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The purpose of this study was to see if specific tests of fitness and movement quality could predict injury resilience and performance in a team of basketball players over 2 years (2 playing seasons). It was hypothesized that, in a basketball population, movement and fitness scores would predict performance scores and that movement and fitness scores would predict injury resilience. A basketball team from a major American university (N = 14) served as the test population in this longitudinal trial. Variables linked to fitness, movement ability, speed, strength, and agility were measured together with some National Basketball Association (NBA) combine tests. Dependent variables of performance indicators (such as games and minutes played, points scored, assists, rebounds, steal, and blocks) and injury reports were tracked for the subsequent 2 years. Results showed that better performance was linked with having a stiffer torso, more mobile hips, weaker left grip strength, and a longer standing long jump, to name a few. Of the 3 NBA combine tests administered here, only a faster lane agility time had significant links with performance. Some movement qualities and torso endurance were not linked. No patterns with injury emerged. These observations have implications for preseason testing and subsequent training programs in an attempt to reduce future injury and enhance playing performance.

The Functional Movement Screen™ (FMS) has demonstrated some efficacy in the prediction of injuries and is thus used by many practitioners to make recommendations for exercise. However, questions remain regarding its utility as a means to evaluate the effectiveness of training. Sixty firefighters volunteered to participate, and their FMS scores were examined before and after 12 weeks of training. Individuals were graded on how they chose to perform rather than how they could perform. The participants were assigned to 1 of 3 groups: intervention 1, intervention 2, or control. The 2 intervention groups received three 1.5-hour training sessions each week and differed in the emphasis that was placed on movement quality. Sagittal and frontal plane videos were used to grade the FMS with 3 methods: the standard 0-3 scale, a 100-point scale that weighted specific compensations (research standard), and a modified 100-point scale whereby grades were assigned based on the total number of compensations present. There were no significant differences in the total FMS scores for any group posttraining. However, the scores of 85% of the firefighters who did not receive training did change. The 100-point scale methods resulted in more FMS score changes posttraining, but the between-group interactions were identical to those found with the standard scoring method. The control group's scores were not consistent pretraining and posttraining; thus, the influence of each intervention could not be evaluated. Currently, the FMS might provide a momentary impression of general movement quality, although further efforts would likely assist in the development of better ways to implement the test, interpret the results, and generate reliable scores.

The purpose of this study was to analyze the effect of 3 different exercise interventions plus a control group on passive hip range of motion (ROM). Previous research studies into the methods of improving passive hip mobility have focused on stretching protocols aimed specifically at the hip joint. The effect of core stabilization, motor training, and myofascial stretching techniques on hip mobility in a selected asymptomatic group with limited hip mobility is unclear. In this study, 24 young men with limited hip mobility (<50th percentile) were randomly assigned to 4 groups: stretching, stretching with motor control exercises for the hip and trunk, core endurance with motor control exercises, and the control group. Six-week home exercise programs were individually prescribed based on the assigned group, hip ROM, movement patterns, and timed core endurance. Two-way analyses of variances were conducted to analyze the effect of group assignment on hip ROM improvements. Both stretching groups demonstrated significant improvements in hip ROM (p < 0.05), attaining hip mobility levels at or above the 75th percentile, with rotation improving as much as 56%. The group receiving core endurance and motor control exercises with no stretching also demonstrated a moderate increase in ROM but only significantly so in rotation. Average core endurance holding times improved 38-53%. These results indicate that stretches aimed at the myofascial components of the upper body, in addition to the hip joint, resulted in dramatic increases in hip ROM in a group of young men with limited hip mobility. Hip ROM also improved in the group that did no active stretching, highlighting the potential role of including stabilization or "proximal stiffening training" when rehabilitating the extremities.

The intent of this study was to quantify spine loading during different kettlebell swings and carries. No previously published studies of tissue loads during kettlebell exercises could be found. Given the popularity of kettlebells, this study was designed to provide an insight into the resulting joint loads. Seven male subjects participated in this investigation. In addition, a single case study of the kettlebell swing was performed on an accomplished kettlebell master. Electromyography, ground reaction forces (GRFs), and 3D kinematic data were recorded during exercises using a 16-kg kettlebell. These variables were input into an anatomically detailed biomechanical model that used normalized muscle activation; GRF; and spine, hip, and knee motion to calculate spine compression and shear loads. It was found that kettlebell swings create a hip-hinge squat pattern characterized by rapid muscle activation-relaxation cycles of substantial magnitudes (∼50% of a maximal voluntary contraction [MVC] for the low back extensors and 80% MVC for the gluteal muscles with a 16-kg kettlebell) resulting in about 3,200 N of low back compression. Abdominal muscular pulses together with the muscle bracing associated with carries create kettlebell-specific training opportunities. Some unique loading patterns discovered during the kettlebell swing included the posterior shear of the L4 vertebra on L5, which is opposite in polarity to a traditional lift. Thus, quantitative analysis provides an insight into why many individuals credit kettlebell swings with restoring and enhancing back health and function, although a few find that they irritate tissues.

Background: Hip mobility is known to affect lumbar spine motion, yet the literature is unclear as to what constitutes normal, limited or excessive motion, given differences in methods, postures, age, etc. The purpose of this study was to establish normative and percentile data for hip rotation and extension, in a young adult male population, using varying methods of quantification., Methods: 77 males (age 18-35) were recruited. Position data was captured using the Vicon Motion capture system, as participants were passively positioned in hip extension (using the Modified Thomas test) and prone hip rotation. 22 of these participants also had measurements obtained with a goniometer. 3D hip extension angles were calculated using Euler angles, and compared to those calculated in 2D. Goniometric results were compared to 2D measurements., Findings: Normal distribution of hip extension and rotation range of motion was established, as were average values for the 5th through 95th percentiles. No significant differences existed between hip extension angles measured with the 2D and 3D approaches. Goniometric measurements of hip extension averaged 3.9° less than 2D, less than 1° different for external rotation, and not different for internal rotation., Interpretation: The normative and percentile data documented here for hip rotation and extension appear to be validly quantified with goniometric techniques when compared to more objective techniques. Further, hip restriction in one plane may not predict restrictions in other planes., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The relationship between muscle activation, force and stiffness needs to be known to interpret the stability state of the spine. To test the relationship between these variables, a quick release approach was used to match quantified torso stiffness with an EMG activation-based estimate of individual muscle stiffnesses. The relationship between activation, force and stiffness was modelled as k = q x F/l, where k, F and l are muscle stiffness, force and length, respectively, and q is the dimensionless stiffness gain relating these variables. Under the tested experimental scenario, the 'stiffness gain', q, which linked activation with stiffness, demonstrated a decreasing trend with increasing levels of torso muscle activation. This highlights the likelihood that the choice of a single q value may be over simplistic to relate force to stiffness in muscles that control the spine. This has implications for understanding the potential for spine instability in situations requiring high muscular demand.

Study Design: Basic scientific investigation employing the medical imaging techniques of contrast-enhanced plane film radiographs and computed tomography in addition to gross dissection techniques on a sample of spines., Objective: To document the specific posterior/posterolateral pathway of mechanically-induced intervertebral disc (IVD) herniation as the result of repetitive loading and disc geometry., Summary of Background Data: In vitro cadaveric and animal investigations have indicated that the posterior/posterolateral aspects of the IVD are most susceptible to damage leading to herniation, and that cyclic bending is the most potent variable influencing herniation. The IVD in horizontal cross-section ranges in shape from ovoid to limacon (kidney-shaped) which influences stress distributions. The purpose of this investigation was to determine the role of the IVDs shape and size on influencing the pathway of herniation., Methods: Compressive loads (1472 N) in conjunction with 7000 repetitive cycles of flexion-extension were applied to 22 porcine motion segments. Computed tomography images and contrast-enhanced plane file radiographs, in addition to dissection techniques were used to evaluate the progression of herniations. A logistical regression assessed the links between endplate size and shape, and the probability of a specific herniation type (directionally diffuse or directionally concentrated)., Results: A total of 18 out of the 22 specimens exhibited detectable anular damage in the posterior/posterior lateral direction. Of the 18 specimens, 17 were partial herniations while one incurred a full herniation. IVD shape was found to be predictive of the pathway of herniation (P = 0.0329); oval IVD shapes were more likely to herniate in a directionally diffuse manner (6/18), while limacon IVDs were more likely to herniate in a directionally concentrated manner (12/18)., Conclusion: The shape of the IVD appears to be predictive of the pathway of IVD herniation.

Normalization of the surface electromyogram (EMG) addresses some of the inherent inter-subject and inter-muscular variability of this signal to enable comparison between muscles and people. The aim of this study was to evaluate the effectiveness of several maximal voluntary isometric contraction (MVC) strategies, and identify maximum electromyographic reference values used for normalizing trunk muscle activity. Eight healthy women performed 11 MVC techniques, including trials in which thorax motion was resisted, trials in which pelvis motion was resisted, shoulder rotation and adduction, and un-resisted MVC maneuvers (maximal abdominal hollowing and maximal abdominal bracing). EMG signals were bilaterally collected from upper and lower rectus abdominis, lateral and medial aspects of external oblique, internal oblique, latissimus dorsi, and erector spinae at T9 and L5. A 0.5s moving average window was used to calculate the maximum EMG amplitude of each muscle for each MVC technique. A great inter-subject variability between participants was observed as to which MVC strategy elicited the greatest muscular activity, especially for the oblique abdominals and latissimus dorsi. Since no single test was superior for obtaining maximum electrical activity, it appears that several upper and lower trunk MVC techniques should be performed for EMG normalization in healthy women.

The main issue addressed here is the paradox of muscle contraction to optimize speed and strike force. When muscle contracts, it increases in both force and stiffness. Force creates faster movement, but the corresponding stiffness slows the change of muscle shape and joint velocity. The purpose of this study was to investigate how this speed strength is accomplished. Five elite mixed martial arts athletes were recruited given that they must create high strike force very quickly. Muscle activation using electromyography and 3-dimensional spine motion was measured. A variety of strikes were performed. Many of the strikes intend to create fast motion and finish with a very large striking force, demonstrating a "double peak" of muscle activity. An initial peak was timed with the initiation of motion presumably to enhance stiffness and stability through the body before motion. This appeared to create an inertial mass in the large "core" for limb muscles to "pry" against to initiate limb motion. Then, some muscles underwent a relaxation phase as speed of limb motion increased. A second peak was observed upon contact with the opponent (heavy bag). It was postulated that this would increase stiffness through the body linkage, resulting in a higher effective mass behind the strike and likely a higher strike force. Observation of the contract-relax-contract pulsing cycle during forceful and quick strikes suggests that it may be fruitful to consider pulse training that involves not only the rate of muscle contraction but also the rate of muscle relaxation.

Background: Epidemiological studies have found associations between lifting, lifting and twisting and twisting alone with increased incidence of disc herniation. This study investigated the role of repeated dynamic axial torque/twist combined with repeated flexion on the disc herniation mechanism., Methods: Porcine cervical spines were tested in one of the following four testing protocols: flexion-extension only; axial torque/twist only; flexion-extension followed by axial torque/twist; or axial torque/twist followed by flexion-extension. Plane film radiographs and computed tomography with contrast in the nucleus were obtained at regular intervals during and following the mechanical testing process together with final dissection to determine the disc injury patterns., Findings: Axial torque/twist in combination with repetitive flexion extension motion, regardless of order, encouraged radial delamination within the annulus (67.5% of specimens). Alternatively, repetitive flexion motion alone encouraged posterior or posterolateral nucleus tracking through the annulus. Axial torque/twist alone was unable to initiate a disc herniation. Both X-ray images with contrast and computed tomography were not good at detecting radial delamination observed during dissection., Interpretation: The clinical relevance is that twisting may cause more radial delamination while repeated flexion causes more posterior tracking of the nucleus giving guidance for both prevention and rehabilitation decisions. In addition, X-ray images with contrast are not effective at detecting the radial delamination which was exacerbated by combined loading in flexion extension and axial torque/twist.

Torso muscles contribute both intrinsic and reflexive stiffness to the spine; recent modeling studies indicate that intrinsic stiffness alone is sometimes insufficient to maintain stability in dynamic situations. The purpose of this study was to experimentally test this idea by limiting muscular reflexive responses to sudden trunk perturbations. Nine healthy males lay on a near-frictionless apparatus and were subjected to quick trunk releases from the neutral position into flexion or right-side lateral bend. Different magnitudes of moment release were accomplished by having participants contract their musculature to create a range of moment levels. EMG was recorded from 12 torso muscles and three-dimensional lumbar spine rotations were monitored. A second-order linear model of the trunk was employed to estimate trunk stiffness and damping during each quick release. Participants displayed very limited reflex responses to the quick load release paradigms, and consequently underwent substantial trunk displacements (>50% flexion range of motion and >70% lateral bend range of motion in the maximum moment trials). Trunk stiffness increased significantly with significant increases in muscle activation, but was still unable to prevent the largest trunk displacements in the absence of reflexes. Thus, it was concluded that the intrinsic stiffness of the trunk was insufficient to adequately prevent the spine from undergoing potentially harmful rotational displacements. Voluntary muscular responses were more apparent than reflexive responses, but occurred too late and of too low magnitude to sufficiently make up for the limited reflexes.

Prolonged sitting with spine flexion has been linked to low back disorders. A variety of mechanisms account for this based on biomechanical and neurological variables. Airline seats typically cause pronounced lumbar flexion due to their hollowed seat back design. A pneumatic support, placed between the seat back and the lumbar spine, was tested to see if lumbar flexion was reduced. Results showed that when the seats were positioned in the upright position, 15 of 20 participants experienced reduced lumbar flexion (by 15 degrees on average) with the support. The study was repeated on the five non-responders with the seatback set in the reclined position. This resulted in another four experiencing less lumbar flexion. Since seated flexion is associated with disc stress, reducing flexion with the support reduced lumbar stress. Spine flexion that results from prolonged sitting is associated with disc stress and pain. The pneumatic support tested here reduced spine flexion. While it is not known why airline seats are designed with no lumbar support, which causes excessive lumbar flexion while seated, the pneumatic support corrected this deficit. Reclining the seatback enhanced this effect.

The objective of this study was to investigate 3 different rowing exercises and quantify the muscle activation of the torso and the hip musculature, together with the corresponding spinal loading and stiffness. Seven healthy male subjects from a university population were instrumented to obtain surface electromyography of selected trunk and hip muscles and to obtain spine position using an electromagnetic spine position sensor, together with video analysis to calculate joint moments. The 3 rowing exercises investigated are the inverted row, standing bent-over row, and the standing 1-armed cable row. The inverted row elicited the highest activation of the latissimus dorsi muscles, upper back, and hip extensor muscles. The lower activation of the lumbar erector spinae muscles during the inverted row corresponded to the lower-spine load measured. The standing bent-over row produced large activation symmetrically across the back but produced the largest lumbar spine load. The 1-armed cable row challenged the torsional capabilities of the trunk musculature. Some "core" exercises may be better for rehabilitation (e.g., having the training goals of modest muscle activation with low spine load), while other exercises may be better for athletic training (e.g., resulting in higher muscle activation and larger spine load). When prescribing "core" exercises, those wishing to spare the low back may choose the inverted row given the lowest spine load exercise. The standing bent-over row elicited large muscle activation symmetrically from the upper to lower back, however induced larger spine loads, but not surprisingly the highest spine stiffness. If torsional endurance or strength is the training goal, the 1-armed cable row might be considered.

Strongman events are attracting more interest as training exercises because of their unique demands. Further, strongman competitors sustain specific injuries, particularly to the back. Muscle electromyographic data from various torso and hip muscles, together with kinematic measures, were input to an anatomically detailed model of the torso to estimate back load, low-back stiffness, and hip torque. Events included the farmer's walk, super yoke, Atlas stone lift, suitcase carry, keg walk, tire flip, and log lift. The results document the unique demands of these whole-body events and, in particular, the demands on the back and torso. For example, the very large moments required at the hip for abduction when performing a yoke walk exceed the strength capability of the hip. Here, muscles such as quadratus lumborum made up for the strength deficit by generating frontal plane torque to support the torso/pelvis. In this way, the stiffened torso acts as a source of strength to allow joints with insufficient strength to be buttressed, resulting in successful performance. Timing of muscle activation patterns in events such as the Atlas stone lift demonstrated the need to integrate the hip extensors before the back extensors. Even so, because of the awkward shape of the stone, the protective neutral spine posture was impossible to achieve, resulting in substantial loading on the back that is placed in a weakened posture. Unexpectedly, the super yoke carry resulted in the highest loads on the spine. This was attributed to the weight of the yoke coupled with the massive torso muscle cocontraction, which produced torso stiffness to ensure spine stability together with buttressing the abduction strength insufficiency of the hips. Strongman events clearly challenge the strength of the body linkage, together with the stabilizing system, in a different way than traditional approaches. The carrying events challenged different abilities than the lifting events, suggesting that loaded carrying would enhance traditional lifting-based strength programs. This analysis also documented the technique components of successful, joint-sparing, strongman event strategies.

Objective: To compare trunk muscle activation patterns and trunk kinematics when using an oscillating blade in standing and unsupported sitting postures, and with different orientations of the blade., Design: A cross-sectional survey of trunk muscle activities and lumbar motion., Setting: Biomechanics research laboratory., Participants: Healthy men (N=13)., Interventions: An oscillating blade was held with 2 hands and oscillated with vertical and horizontal orientations of blade. These exercises were performed both in an erect standing position and in an erect sitting position., Main Outcome Measures: Surface electromyography from 14 trunk and 2 shoulder muscles, together with lumbar angular displacement in the 3 planes of motion, were measured while subjects used an oscillating blade at different performance variations. Electromyographic signals were normalized to isometric maximal voluntary contraction (MVC) amplitudes., Results: With the exception of internal oblique and anterior deltoid for the horizontal condition, and erector spinae at L5 level for the vertical condition, the subject's posture had no effect on trunk muscular recruitment when using the oscillating blade. The vertical blade orientation resulted in higher amplitudes of spine rotation on the horizontal plane and produced the greatest activation levels of the internal oblique (47% MVC), pectoralis major (33% MVC), and external oblique (23% MVC). On the other hand, the horizontal orientation resulted in the greatest activation levels of erector spinae at T9 level (28% MVC), latissimus dorsi (26% MVC), and rectus abdominis (17% MVC)., Conclusions: Muscle activation and spine motion from using an oscillating blade were not affected by the standing or sitting posture of the subject. The choice of blade orientation was more important, because it defined the main group of muscles recruited during the exercise.

Objective: To determine the utility of the active straight leg raise (ASLR) test as a screen of lumbar spine stability and abdominal bracing (AB) ability., Design: A biomechanical study of the ASLR test as a clinical evaluation of lumbar spine stability and AB., Setting: Clinical research laboratory., Participants: Fourteen participants who were currently asymptomatic for back pain and leg pain were evaluated., Methods: Spine posture, muscle activation, and pressure distributions underneath the supine subject were determined., Main Outcome Measurements: An estimation of lumbar spine stiffness, a direct correlate with spine stability, was obtained using an anatomically detailed spine model., Results: AB during the ASLR reduced the center of pressure (CoP) movement on a strain-based pressure mat in lumbar rotation (P < .0125) as well as reducing directly measured lumbar rotation (P = .02). Active AB increased lumbar spine stiffness (P < .002). Regression analysis between stiffness and CoP movement suggested that different participants used different strategies to control torso motion., Conclusions: This study demonstrates that the ASLR has utility as a screen of lumbar spine stability and AB ability. The ASLR maneuver can assess control of lumbar rotational movements in the transverse plane. Finally, this study demonstrated that AB can measurably improve the rotational (transverse plane) stiffness of the lumbar spine.

The purpose of this study was to document the muscle activity and spine motion during several tasks requiring rapid abdominal contraction. Eight healthy men from a university population were instrumented to obtain surface electromyography of selected trunk and hip muscles, together with video analysis to calculate joint moments and electromagnetic lumbar spine position sensor to track spine posture. Exercises included a punch, throw, and a ballistic torso-stiffening maneuver. This study found that no muscle turned on significantly before any other muscle during both the 1-in. punch and ballistic torso-stiffening maneuver. Conversely, there was a significant order or muscle onset during the baseball throw. Muscles reached peak activation significantly before any other muscle during the baseball throw and 1-in. punch, but there were no significant differences for the torso-stiffening maneuver. The exercises quantified in this study demonstrated how muscle contraction dynamics change to meet differing demands for stiffening, for force/moment production, and for rapid movements. Specifically, it seems that there is an order of contraction when movement is the goal but not when just spine stability is required. Thus, a different intensity of abdominal bracing is required to achieve the different objectives of sports tasks and exercises.

The purpose of this study was to document the muscle activity, spine motion, spine load, and stiffness during several movement-based or "functional" exercises and to assess the effect of technique change. Eight subjects, all healthy men from a university population, were instrumented to obtain surface electromyography of selected trunk and hip muscles, together with video analysis and electromagnetic lumbar spine position sensor to track spine posture. Exercises included a walkout in the sagittal plane that compared an upright form against a wall with those performed on the floor, overhead cable pushes, lateral cable walkouts, the good morning exercise, and the bowler's squat. Generally, muscle activation levels were quite modest even though the tasks were quite strenuous in many cases. Even though similar joint moments were required in different exercises, the pattern of activity between muscles was different. Abdominal bracing increased spine stiffness at the expense of more spine load. Thus, muscle activity seems to be constrained in "functional" exercises. There are several possible reasons for this. Single muscles cannot be activated to 100% of the maximum voluntary contraction in functional exercises because this would upset the balance of moments about the 3 orthopedic axes of the spine, or it would upset the balance of stiffening muscles around the spine required to ensure stability of the spinal column. The one exception was the floor walkout, which resulted in full activation of the rectus abdominis; however, this was a sagittal plane task without the joint moment constraints of multiplanar exercise. Therefore, maximal muscle activity is observed during single-plane tasks, but muscle activation levels were constrained during functional tasks. Thus, strength training muscles may not help in "functional multiplanar" tasks. These data can be used to assist decisions regarding the selection of exercises, specifically choices regarding the starting challenge, progression, exercise form, and possibly corrective technique for those who have spine concerns, or those simply looking for performance enhancement.

Study Design: A basic science study that used a porcine cervical spine model to produce disc prolapse subsequently exposed to an extension protocol., Objective: This study investigated whether extension or combined extension and side flexion could move the displaced portion of nucleus from the anulus towards the nucleus., Summary of Background Data: Previous research has established that repeated flexion can create disc prolapse, the question here is whether repeated extension can reverse the process., Methods: The C3/4 segments of 18 porcine cervical spines were dissected and potted in cups. Specimens were preloaded, then axially compressed (1472 N), and repeatedly rotated in either pure flexion or combined flexion and side flexion at a rate of 0.5 degrees /s. Specimens that prolapsed were axially compressed and repeatedly and rotated into extension., Results: Based on a blinded radiologist's review of the radiograph images, all 18 specimens contained healthy discs before testing, but after testing 2 of the 18 specimens had endplate fractures, whereas 11 of the 18 specimens had prolapsed. Prolapsed nucleus was reduced in 5 of the 11 prolapsed specimens after the reversal testing, whereas the remaining 6 did not change. Subclassification analysis revealed that the prolapsed discs that centralized had significantly less disc height loss (P < 0.01). Neither the classification of the herniation (circumferential or radial) nor the angle of lordosis of the specimens was linked to the behavior of the specimens., Conclusion: This study showed that with repeated flexion, in porcine cervical spines, disc prolapse was initiated and that the displaced portion of nucleus can be directed back towards the center of the disc in response to particular active and passive movements/positions.

The ProFitter 3-D Cross Trainer is a labile surface device used in the clinic and claimed to train spine stability. The purpose of this study was to quantify the spine mechanics (compression and shear forces and stability), together with muscle activation mechanics (surface electromyography) of the torso and hip, during three ProFitter exercises. Trunk muscle activity was relatively low while exercising on the device (<25%MVC). Gluteus medius activity was phasic with the horizontal sliding position, especially for an experienced participant. Sufficient spinal stability was achieved in all three exercise conditions. Peak spinal compression values were below 3400 N (maximum 3188 N) and peak shear values were correspondingly low (under 500 N). The exercises challenge whole-body dynamic balance while producing very conservative spine loads. The motion simultaneously integrates hip and torso muscles in a way that appears to ensure stabilizing motor patterns in the spine. This information will assist with clinical decision making about the utility of the device and exercise technique in rehabilitation and training programs.

Study Design: In situ testing of the rat abdominal wall., Objective: To test the ability of muscularly generated force and stiffness to be transmitted between the layers of the abdominal wall., Summary of Background Data: The abdominal wall is comprised of 3 obliquely oriented sheet-like muscles bound together through a connective tissue network. This anatomic arrangement would seem ideal to facilitate myofascial force transmission, which if present would indicate shear connections between the muscle layers that could have important mechanical consequences., Methods: In 10 Sprague-Dawley rats, the 3 layers of the abdominal wall were isolated together and attached to a servomotor force/displacement system. The abdominal wall was stimulated via electrodes over the surface of the transverse abdominis, and measures of force and stiffness were obtained. The aponeurosis attaching the transverse abdominis to the rectus sheath was then cut and the wall was restimulated and the same measures were again obtained., Results: Active force and stiffness were both reduced in the cut aponeurosis state. These drops were much lower (10.6% and 10.7%, respectively) than would be expected if the transverse abdominis were completely removed. Furthermore, a control group (5 rats), in which the aponeurosis was not cut, but a similar amount of time to that necessary to perform the aponeurosis surgery was allowed to elapse, showed reductions in active force and stiffness (7.9 and 8.2, respectively) nearing that seen in the cut state. This indicates that at least a portion of this drop was due to the passage of time in the compromised surgical state., Conclusion: It was concluded that the majority of the force and stiffness generated by the transverse abdominis was transferred through the connective tissue network adhering to the internal oblique muscle. This indicates the presence of strong shear connections between the muscular layers, which suggests a composite stiffening function of the architectural design.

The theme developed in this position paper follows the current evolution of injury prevention in the backs of workers. Job change or 'fitting the task to the person' has come far, but will probably not result in zero injury rates. This is because the cause of injury is heavily influenced by the way that a worker moves. A review of injury mechanisms reveals the need for the biomechanist/ergonomist to incorporate features in biomechanical models that recognise these injury mechanisms. The implication of one such model is that the next leap toward a zero injury rate may be approached with 'fitting the person to the task' or at least retraining the way that workers move. A few examples of movement-based back injury prevention strategies are provided. Finally, some thoughts on implementing such an approach are expressed. This is a review and position paper written in honour of Professor Don Chaffin's career.

Objective: To quantify several forms of the curl-up, side-bridge, and birddog exercises (muscle activity and 3-dimensional [3D] spine position) including some corrective techniques to assist clinical decision-making., Design: A basic science study of a convenience sample with a retest of expert intervention., Setting: Spine Biomechanics Laboratory/Research Clinic., Participants: Healthy men (N=8) performed the exercises, and 5 subjects repeated the exercises as an expert applied corrective techniques., Interventions: Not applicable., Main Outcome Measures: Surface electromyography of selected trunk and hip muscles together with video analysis and 3D spine posture were collected., Results: Comparison of muscle activation levels showed there were justifiable progressions in each exercise form. In general, bracing of the abdominal wall enhanced activation of the obliques, but different techniques caused migration of muscle activity to other muscles. Examples of specific findings include the following. Movement during these traditionally isometric exercises such as drawing squares with the hand/foot while in the birddog posture enhances activation of many muscle groups. Breathing while holding the isometric exercises had differing effects on muscle activation which was exercise dependent. Some corrective exercise techniques, such as fascial raking, substantially changed relative activation between muscles in the abdominal wall., Conclusions: The data presented in this study may be used to guide the clinical decision process when choosing a specific exercise form together with selecting the correct starting level, a logical progression, suitable dosage, and possible corrective technique to enhance tolerance of a patient.

The abdominal wall components, specifically muscle and connective tissue, must meet and accommodate a wide range of force demands for torso movement, spine stabilization, and respiration. It has a composite laminate nature that may lend itself to facilitating the required tissue responses. The purpose of this exploratory study was to examine the deformations of the abdominal wall connective tissues, with a special focus on both the internal oblique aponeurosis and the tendinous intersections of the rectus abdominis, using ultrasound imaging, during relatively simple contractions of the abdominal musculature. There were two main findings of this study: (1) deformations occurred in nearly 50% of contractions that would be characterized by a simultaneous expansion in multiple planes; (2) the laterally generated forces of the oblique and transverse muscles transfer a great deal of force across the rectus abdominis muscle and sheath, leading to a lateral movement of the rectus muscle during abdominal contraction.

Objective: To determine if spine stability would be affected by the competing demands of simultaneous challenged ventilation and supporting a hand-held load., Design: Subjects were their own controls in a repeated measures design where a single task was repeated, once in a different condition, in a random order., Background: Muscle stiffness influences spine stability. The same muscles that contribute to spine stability assist in challenged breathing. We hypothesized that a challenged ventilation task would place low back pain (LBP) sufferers at risk of spine instability., Methods: Subjects (14 normal; 14 with low back pain) performed two trials with a 22kg hand-held weight and the trunk angled forward at 30 degrees . One trial was of 60s duration while breathing ambient air, the other of 70s duration, while breathing 10% carbon dioxide. Spine stability and compression were quantified, using an EMG assisted optimization model in both trials., Findings: Contrary to expectation, spine stability increased during the challenged breathing trials compared to the ambient air condition for subjects with a history of low back pain when abdominal muscle activity was accounted for as a covariate., Interpretation: Subjects with a history of low back pain had higher stability in challenged breathing trials, indicating that some active mechanism protects the spine for the LBP groups in challenging situations. This may be to provide some margin of safety for damaged passive tissues but could be adversely affected by fatigue in the longer term.

Previous studies analyzing neuromuscular independence of the abdominal wall have involved a participant population with no specific training in separating individual muscle segments. We chose to study nine women trained in the art of middle-eastern dance, anticipating they may have unique skills in motor control. Specifically, we were searching for evidence of separation of upper rectus abdominis (URA) from lower rectus abdominis (LRA), as well as understanding what role the oblique muscles play in abdominal wall synergies. EMG analysis was done on eight trunk muscles bilaterally as the dancers participated in 30 dance, planar, and curl-up activities. The filtered data were then cross-correlated to determine the time lag between pairs of signals. Only three dance movements demonstrated consistent evidence of an ability to separate URA/LRA activation timing. The external and internal oblique muscles tend to align themselves temporally with the LRA. However, these findings were only evident in these three specific "belly-roll" conditions, all with low levels of muscle activation, and no external torque. Evidence of significantly different activation levels (% MVC) between URA/LRA was demonstrated in eight conditions, all of which required various pelvis movements with minimal thorax motion.

Spine stability is ensured through isometric coactivation of the torso muscles; however, these same muscles are used cyclically to assist ventilation. Our objective was to investigate this apparent paradoxical role (isometric contraction for stability or rhythmic contraction for ventilation) of some selected torso muscles that are involved in both ventilation and support of the spine. Eight, asymptomatic, male subjects provided data on low back moments, motion, muscle activation, and hand force. These data were input to an anatomically detailed, biologically driven model from which spine load and a lumbar spine stability index was obtained. Results revealed that subjects entrained their torso stabilization muscles to breathe during demanding ventilation tasks. Increases in lung volume and back extensor muscle activation coincided with increases in spine stability, whereas declines in spine stability were observed during periods of low lung inflation volume and simultaneously low levels of torso muscle activation. As a case study, aberrant ventilation motor patterns (poor muscle entrainment), seen in one subject, compromised spine stability. Those interested in rehabilitation of patients with lung compromise and concomitant back troubles would be assisted with knowledge of the mechanical links between ventilation during tasks that impose spine loading.

Objective: This study evaluates if side posture lumbar manipulation is associated with a refractory period of the audible "crack" and if so, to quantify this refractory period across subjects., Methods: Three subjects were exposed to multiple "baseline" side posture manipulations until no further audible cracks were recorded. "Test-refractory period" manipulations were administered after a set time (ie, potential refractory period) at which point the number of audible cracks was recorded. The refractory period was declared when a minimum of 50% of the baseline audible "cracks" had recovered during the test manipulations. The study design included 2 clinicians who performed side posture lumbar manipulation on asymptomatic subjects ranging from 38 to 49 years of age., Results: The refractory period was 40 minutes for subject A, 70 minutes for subject B, and 95 minutes for subject C. The average refractory period across subjects was 68.33 minutes. The audible "crack" recovery was maintained for the remaining test days once the refractory period had been met., Conclusions: The audible "crack" heard during side posture lumbar manipulation is believed to originate from the zygapophyseal joints. This is supported by the presence of a refractory period and by the number of audible "cracks" found per manipulation.