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BACKGROUND: The relationship between strength and throwing velocity is much investigated in handball, but core strength is largely ignored. Only four studies have investigated the effect of core training on handball throwing velocity, reporting conflicting results in amateur players. However, lack of specificity and deficient technical execution of throwing in amateurs can obscure the results. OBJECTIVE: To examine the direct association between trunk flexion strength and throwing velocity in elite handball players, using women as a model. METHODS: Sixteen women players from an elite-level Norwegian handball team participated in the study. Strength in trunk flexion, shoulder extension, internal shoulder rotation, and forearm pronation was assessed using isokinetic dynamometer measurements (peak moment, total work, angular impulse). Throwing velocity in both the standing throw with run-up and the jump throw was determined from motion capture measurements. To account for arm strength, the association between trunk flexion strength and throwing velocity was examined using partial correlation analyses. RESULTS: No significant association was found between any measure of trunk flexion strength and throwing velocity for either throwing technique (explained variance ⩽ 13.7%). CONCLUSIONS: The results indicate that isolated, dynamic trunk flexion strength is not a differentiating factor for handball throwing velocity in elite women players.

Kicking is fundamental in many field-based sports. Most studies investigating kicking performance have been conducted with male athletes, resulting in a dearth of specific data to inform coaching of this skill in female players. This systematic review aimed to compare kicking biomechanics in male and female athletes in field-based sports. As per PRISMA guidelines, articles were retrieved from searches across five online databases. Studies investigating kicking biomechanics in field-based athletes of both sexes were eligible for inclusion. Articles were screened using Covidence and data extracted based on STROBE recommendations. The review included 23 studies, featuring 455 soccer players. Male athletes produced significantly greater ball velocities and linear velocities of the ankle, foot, and toe than females. Males had greater ankle plantarflexion angles than females at ball strike, while females used larger trunk flexion ranges than males. Hip and knee torques and ball-to-foot velocity ratios were greater in men than women. Skilled players generated power using tension arcs; a technique not seen in novices. Skill level within sex may have a greater influence on kicking performance than differences between the sexes. This review highlights the need for further research investigating kicking performance in both sexes across the spectrum of sports.

Objective: In 2020, coronavirus disease-2019 (COVID-19) became the cause of a pandemic. In response, the Japan Sports Agency issued warnings about secondary damage to health, such as the threat to physical and mental well-being due to the lack of exercise in this situation. In this study, we report on cross-sectional and longitudinal examinations of standing trunk flexion to evaluate how temporary long-term school closures affected musculoskeletal function in elementary school students. Patients and Methods: All children in one public elementary school in T-city during the school years 2019 and 2020 were included in this study. A digital forward flexion meter was used to measure standing trunk flexion. Results: In this study, 284 (284/289: 98.3%) and 266 (266/274: 97.1%) children in school years 2020 and 2019, respectively, were found to have valid data for cross-sectional analysis. The standing trunk flexion did not show significant differences between grades or sexes. In the longitudinal analysis, the results of the comparison of standing trunk flexion in children for two consecutive years revealed significant differences only between grades 3 and 4 (P

Purpose The aim of the present study was to evaluate the trunk strength capacity of alpine ski racers aged 10–18 years, who were tested during the last 15 years, to identify reference values for trunk flexor to extensor strength ratios according to age and sex. Methods In total, 2841 participants (1605 males, 1236 females; 10–18 years) were included, who were pupils of a famous skiing-specific secondary modern school or members of the provincial ski team between 2006 and 2020. The maximum isometric trunk flexion and extension strength was measured using the slightly modified Back Check. Sex-specific differences were assessed with Student’s t test or Mann–Whitney-U test. Univariate analyses of variance or Kruskal–Wallis-H tests were used to assess differences between age groups. Descriptive sex- and age-specific reference values were calculated (norm area: mean ± ½ standard deviation). Results Sex-specific differences were found for both flexion (starting at 11 years) and extension strength (starting at 12 years) (P Conclusion The present study provides age- and sex-specific reference values for trunk flexion to extension strength ratios for 10- to 18-year old youth and adolescent ski racers. The data of the present study represent a large data pool of youth ski racers at a high-performance level; thus, coaches can use the reference values for comparing the ratios of their athletes.

Background The head, arms and trunk segment constitute a large proportion of the body’s mass. Therefore, small alterations in trunk inclination may affect lower limb joint moments and muscle activation patterns. Although previous research has investigated the effect of changing frontal plane inclination of the trunk, it is not clear how increasing trunk flexion will impact on the activation of the lower limb muscles. Research question What is the effect of independently manipulating trunk flexion angle on lower limb kinematics, moments and muscle function? Methods Gait analysis was carried out on 20 healthy people under four trunk flexion conditions: normal walking (NW), NW-5°, NW+5° and NW+10°. For the latter three conditions, a biofeedback approach was used to tightly control trunk flexion angle. A linear mixed model was used to investigate the effect of changing trunk flexion on joint angles, moments, and knee muscle activation. Results There were clear increases in hip and ankle moments as trunk flexion was increased, but no change in knee moments. The results also showed a linear increase in knee flexor muscle activity and a corresponding increase in co-contraction as trunk flexion increased. Interestingly, there was a dramatic change in the profile of hamstring activity. In the medial hamstrings, this change led to a 100% increase in activation during early stance as flexion was increased by 5° from NW. Significance This is the first study to demonstrate a strong dependence of knee flexor muscle activity on trunk flexion. This is important as people with knee osteoarthritis have been observed to walk with elevated muscle activation and this has been linked to increased joint loads. It is possible that these altered muscle patterns may result from increased trunk flexion during walking.

[Purpose] The purpose of this study was to develop a simpler method to estimate the intervertebral disc compressive force in healthy older adults. We also examined the validity of a simpler estimation formula for patients with spinal diseases. [Participants and Methods] Fifty-two older adults participated in the study. The standing posture was measured using a three-dimensional motion capture system. The intervertebral disc compressive force was calculated using a previously reported method. Correlation analysis was used to detect the relationship between the measured parameters and the intervertebral disc compressive force. Multiple regression analysis was performed to obtain an equation for the intervertebral disc compressive force. Correlation analysis was used to determine the regression equation for the patients with spinal diseases. [Results] Multiple regression analysis showed that trunk flexion/extension angle and body mass were significantly associated with intervertebral disc compressive force. A correlation was found between the measured and predicted values in the healthy older adults, whereas both values were inconsistent in patients with spinal diseases. [Conclusion] The results of our study demonstrated that the trunk flexion/extension angle and body mass are indicators of intervertebral disc compressive force and can be used to assess low back mechanical stress in healthy older adults.

O objetivo deste estudo foi investigar a existência de associação entre a Movimentação Manual de Cargas (MMC) e lombalgia ocupacional em carregadores da Central de Abastecimento de Sergipe (CEASA/SE). Para tanto, um estudo observacional analítico foi conduzido com 60 carregadores. As variáveis investigadas foram coletadas mediante formulário estruturado e instrumentos de medição específicos. Os dados foram tratados estatisticamente e o nível de significância fixado em p

Objective A computer vision method was developed for estimating the trunk flexion angle, angular speed, and angular acceleration by extracting simple features from the moving image during lifting. Background Trunk kinematics is an important risk factor for lower back pain, but is often difficult to measure by practitioners for lifting risk assessments. Methods Mannequins representing a wide range of hand locations for different lifting postures were systematically generated using the University of Michigan 3DSSPP software. A bounding box was drawn tightly around each mannequin and regression models estimated trunk angles. The estimates were validated against human posture data for 216 lifts collected using a laboratory-grade motion capture system and synchronized video recordings. Trunk kinematics, based on bounding box dimensions drawn around the subjects in the video recordings of the lifts, were modeled for consecutive video frames. Results The mean absolute difference between predicted and motion capture measured trunk angles was 14.7°, and there was a significant linear relationship between predicted and measured trunk angles ( R2 = .80, p < .001). The training error for the kinematics model was 2.3°. Conclusion Using simple computer vision-extracted features, the bounding box method indirectly estimated trunk angle and associated kinematics, albeit with limited precision. Application This computer vision method may be implemented on handheld devices such as smartphones to facilitate automatic lifting risk assessments in the workplace.

Background Abdominal draw-in maneuver (ADIM) has been recommended to achieve appropriate trunk muscle response for patients with non-specific chronic low back pain (CLBP). However, it has remained unclear whether the intervention with ADIM could change the trunk muscle response to sudden release from loading, which is considered to contribute mechanical circumstances to low back pain. The purpose of the present study was to investigate the effects of the intervention with ADIM on electromyography (EMG) activities of trunk muscles following sudden release from loading. Methods Seventeen subjects with non-specific CLBP participated. Subjects resisted trunk flexion or extension loading in semi-seated position, and then the loading was suddenly released. EMG recordings of 6 trunk muscles were acquired using a wireless surface EMG system. Onset and offset times were calculated from the EMG data. The intervention with ADIM was provided for 4 weeks. The onset and offset times were compared between pre- and post-intervention with ADIM. Results At the post-intervention, the onset of trunk flexors following release from trunk flexion loading became significantly earlier than pre-intervention (P = 0.028). The offset of flexors following release from trunk extension loading of post-intervention was significantly earlier than that of pre-intervention (P = 0.001). Conclusions We showed that the intervention with ADIM changed the EMG activity of trunk flexors in response to sudden release from loading. These results suggest a possibility that ADIM might be effective to improve the neuromuscular control of trunk flexors for the treatment of young patients with non-specific CLBP.

Background: The chronic low back pain (LBP) had been considered an important occupational disorder with several strategy available to treatment, however, few studies had been evaluated the treatment combination. Objectives: The aim of present study was compared the effects of combination of crocheting associated to Kinesiotherapy treatment and Kinesiotherapy isolated treatment on function of lumbar spine and pain during achievement of daily life in patients with chronic LBP. Methods: Forty subjects were distributed randomly in two groups: Crochetagem + Kinesioterapy (C; n: 18; 47.5 ± 7.75 years) and Kinesiotherapy (K, n: 18; 45.3 ± 8.93 years). The C group was treated by crocheting technique associated with kinesiotherapy using therapeutic ball. The K group performed a kinesiotherapy treatment using just a therapeutic ball. The following parameters were evaluated: abdominal strength, articular range motion and the data of Rolland Morris and Oswestry Disability Index questionnaires were evaluated before and after 8 weeks of treatment. Both groups performed all therapeutic sessions for 50 minutes, three times a week. Results: Significant differences (p

Occupational Abstract The aim of this project was to develop and test an application capable of quickly and repeatedly measuring trunk flexion angles during sagittal plane lifting tasks. The developed application uses the built-in accelerometer in mobile devices to approximate trunk flexion angle, as the user follows an operator as they perform a lift. A black line is superimposed over the camera feed, allowing the user to approximate the angle of inclination of a line connecting the operator's seventh cervical and first sacral vertebrae-thereby estimating the trunk flexion angle. The magnitude of this angle and its velocity have been linked to the development of occupational low back pain; thus the application provides ergonomists a more refined means of screening tasks beyond currently available survey tools.

Objective: Many caregivers often carry infants using baby carriers until they are approximately 36 months old. The purpose of this study was to...

The purpose of this pilot case study is to investigate the effects of Pi-lates training on hamstring/quadriceps ratio, trunk strength, shoulder strength, and body composition in adolescent baseball players. Eight adolescent baseball players, 15 years of age, participated in Pilates program (supervised training, 50 min per session for three times a week for 8 weeks) using reformer and Cadillac. The intensity of the program was progressively increased by applying beginner level for 1–2 weeks, intermediate level for 3–6 weeks, and advance level for 7–8 weeks. To verify the effect of the Pilates program on hamstring/quadriceps ratio, trunk strength, shoulder strength and body composition, participants performed bioelectrical impedance analysis and isokinetic testing at pre- and posttraining. After the Pilates training, there were significant increases in body weight (P

[Purpose] To compare flexion and extension peak torque of patients with nonspecific-chronic low back pain who were classified as directional preference subgroups, and their matched healthy controls. [Participants and Methods] Fifty male volunteers (25 with non-specific chronic low back pain and 25 healthy-matched controls) consented to participate. The investigator collected all demographic data, hips, knees and spinal mobility in addition to the peak torque using the Biodex isokinetic dynamometer. The measurement protocol consisted of 2 sets of 10 consecutive flexion-extension efforts performed at 120°/sec and 60°/sec angular velocity. A two minutes rest period was given between sets. The preset 50° range of motion included 20°(+20°) of trunk extension and 30°(-30°) of trunk flexion. [Results] A 2 × 2 mixed-design ANOVA showed a significant group X isokinetic velocity interaction. The main effect of isokinetic velocity was also significant. In reference to the peak torque of the flexors of the trunk, the main effect of group was significant. [Conclusion] The extension peak torque significantly depends on the velocity of the isokinetic dynamometer; however the flexion peak torque significantly depends on the participants' group attribution.

Hamstring shortness and postural deformities are frequent in adolescents. For this reason, the purpose of this study was to analyse the influence of a short-term stretching program in hamstring extensibility and sagittal spinal curvatures in high school students. Sixty-two male high school students aged 14-17 years old performed a 70 seconds hamstring stretching program (3 exercises) twice a week for five weeks during their physical education classes. Hamstring extensibility was measured by the straight leg raise test and sit-and-reach test. Thoracic and lumbar curves and pelvic inclination were measures in relaxed standing and in the sit-and-reach test. These measures were assessed before (pre-test) and after (post-test) the intervention program. Significant increases in the sit-and-reach score (d= 0.23) and in the straight leg raise angle (d= 0.85-0.90) were found. Sagittal spinal curvatures in standing showed no differences between pre- and post-test. In the maximal trunk flexion position during the sit-and-reach was detected a lower thoracic kyphosis and posterior pelvic tilt (p < 0.05) in post-test although with a low size effect (d=0.02-0.22). A hamstring muscle stretching program with a volume of 2 sessions per week (70 seconds each session), for 5 weeks, improves hamstring extensibility in adolescents and slightly reduces the thoracic bending and posterior pelvic tilt in trunk flexion postures with extended knees Debido a la frecuencia de casos con una reducida extensibilidad isquiosural y alteraciones posturales en adolescentes, el objetivo de este estudio fue analizar la influencia de un programa de estiramientos, de corta duración, en la extensibilidad isquiosural y disposición sagital del raquis en estudiantes de Educación Secundaria. A sesenta y dos adolescentes varones (14-17 años) se les midió la extensibilidad isquiosural (test sit-and-reachy test de elevación de la pierna recta) antes (pre-test) y después (post-test) de un programa escolar de 5 semanas (2 sesiones semanales), compuesto por tres estiramientos de la musculatura isquiosural, con una duración total por sesión de 70 segundos. También se valoró la disposición sagital del raquis torácico, lumbar e inclinación pélvica en bipedestación relajada y en el sit-and-reach. Se encontró un aumento significativo en la distancia alcanzada en el test sit-and-reach (d= 0,23) y en el ángulo de flexión co-xofemoral en el test de elevación de la pierna recta (d= 0,85-0,90). La disposición sagital del raquis en bipedesta-ción no mostró diferencias entre el pre- y post-test. En la posición de máxima flexión del sit-and-reach, hubo una menor cifosis torácica y menor retroversión pélvica (p < 0,05) en el post-test, aunque con un tamaño del efecto bajo (d=0,02-0,22). Un programa de estiramientos de la musculatura isquiosural realizado en las dos clases semanales de Educación Física (70 segundos de estiramiento en cada clase), durante 5 semanas, mejora la extensibilidad isquiosural de adolescentes y reduce, ligeramente, la flexión torácica y la retroversión pélvica en la posición de máxima flexión del tronco con rodillas extendida Actividad Física y Deporte

Objective: To observe the efficacy of bilateral subthalamic nucleus deep brain stimulation on Pisa syndrome in patients with Parkinson's disease.Methods: A total of 52 patients with Parkinson's disease who underwent deep brain stimulation in Beijing Hospital from July 1, 2016 to July 1, 2020 were reviewed. The clinical data were collected for the patients who met the diagnostic criteria of Pisa syndrome on “Medication-Off” state pre-operatively.Results: Two patients met the diagnostic criteria of Pisa syndrome before operation, with a Pisa angle of 10 and 14°, respectively. The lateral trunk flexion of the two patients improved after operation. In stimulation-on/medication-off state, the Pisa angle decreased from 10 to 2° and from 14 to 6°, respectively.Conclusion: Bilateral subthalamic nucleus deep brain stimulation might have beneficial effects on lateral trunk flexion in PD patients, but the predictors of curative effect are not clear.

Introduction: Elite youth soccer players suffer increasing numbers of injuries owing to constantly increasing physical demands. Deficits in neuromuscular performance may increase the risk of injury. Injury risk factors need to be identified and practical cut-off scores defined. Therefore, the purpose of the study was to assess neuromuscular performance parameters within a laboratory-based injury risk screening, to investigate their association with the risk of non-contact lower extremity injuries in elite youth soccer players, and to provide practice-relevant cut-off scores.Methods: Sixty-two elite youth soccer players (age: 17.2 ± 1.1 years) performed unilateral postural control exercises in different conditions, isokinetic tests of concentric and eccentric knee extension and knee flexion (60°/s), isometric tests of hip adduction and abduction, and isometric tests of trunk flexion, extension, lateral flexion and transversal rotation during the preseason period. Non-contact lower extremities injuries were documented throughout 10 months. Risk profiling was assessed using a multivariate approach utilizing a Decision Tree model [Classification and Regression Tree (CART) method].Results: Twenty-five non-contact injuries were registered. The Decision Tree model selected the COP sway, the peak torque for knee flexion concentric, the functional knee ratio and the path of the platform in that hierarchical order as important neuromuscular performance parameters to discriminate between injured and non-injured players. The classification showed a sensitivity of 0.73 and a specificity of 0.91. The relative risk was calculated at 4.2, meaning that the risk of suffering an injury is four times greater for a player, who has been classified as injured by the Decision Tree model.Conclusion: Measuring static postural control, postural control under unstable condition and the strength of the thigh seem to enable a good indication of injury risk in elite youth soccer players. However, this finding has to be taken with caution due to a small number of injury cases. Nonetheless, these preliminary results may have practical implications for future directions in injury risk screening and in planning and developing customized training programs to counteract intrinsic injury risk factors in elite youth soccer players.

We conducted a retrospective study to test our hypothesis that the subjective postural vertical (SPV) ratio, i.e., SPV in relation to the lateral flexion axis, is predictive of lateral trunk flexion (LTF) in patients with Parkinson's disease (PD). The study group comprised 25 patients with PD. The SPV angle, i.e., the subjective perception of a vertical position with reference to the vertical axis, and the SPV ratio, i.e., the SPV angle with reference to the axis of lateral flexion, were calculated. The SPV ratio (r = 0.698 p = 0.001) and LTF angle (r = −0.601 p = 0.001) were found to correlate with change in the LTF angle calculated at 1 year. The SPV ratio was significantly smaller in the LTF angle-improved group (n = 12) than in the non-improved group (n = 13) (0.99 ± 0.78 vs 1.66 ± 0.71, p = 0.011). The AUC under the ROC curve of the SPV ratio for discrimination of LTF improvement was 0.795 (95% confidence interval: 0.61–0.98). Our study showed that the SPV ratio is associated with change in the LTF and that the SPV ratio can conceivably be used to predict the likelihood of improvement in patients’ LTF.

Trip-specific training improves the kinematics of trip-specific compensatory stepping response (CSR) in the laboratory and reduces prospectively measured trip-related fall-rate of middle age and older women. We examined whether one session of trip-specific perturbation training could improve recovery step kinematics in women with knee osteoarthritis (OA), a condition known to increase fall risk. Seventeen women with self-reported symptomatic knee OA (age 61.1 ± 7.7 years, body mass index [BMI] 29.7 ± 5.9 kg/m2 ) and 22 control women (age 59.5 ± 6.8 years, BMI 28.4 ± 6.2 kg/m2 ) completed a brief training protocol consisting of 20 trials of treadmill-delivered trip-specific perturbations. We assessed pre- and post-training recovery step length and trunk kinematics at the instant of recovery step completion. Repeated-measures analysis of variance was used to determine the significance of between-group differences following the training protocol, and to evaluate the significance of within-group pre-to-post changes in the variables of interest. The group by training interaction effects for step length (p = 0.466), trunk flexion angle (p = 0.751), and trunk angular velocity (p = 0.413) were not significant and the pre-to-post changes in step length were not significant (p = 0.286). However, pre-to-post trunk flexion angle improved by 26% and 34% in the OA and control groups, respectively (p < 0.001) and trunk flexion angular velocity decreased by 193% in the OA group and by 32% in the control group, respectively (p < 0.001), often reflecting a transition to the direction of extension. The results suggest that trip-specific training can improve CSR kinematics in women with knee OA. It is important to determine, the effectiveness of trip-specific training in decreasing trip-specific fall-rate by women with knee OA. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:663-669, 2020.

The biomechanics of the golf swing have received considerable attention in previous research. However, existing studies have focused on young athletes, while the kinematics of older golfers remain poorly documented. This study presents kinematic data for healthy senior golfers during swings performed with a driver and six-iron. Seventeen male golfers (62.2 ± 8.8 years) volunteered for participation and a 10-camera Vicon system (Oxford, UK) recorded kinematic data (500 Hz). A launch monitor (TrackMan, Vedbaek, Denmark) recorded club head speed and initial ball speed. Joint angles and peak velocities of the trunk and lower body were extracted at the top of the backswing, ball contact, and end of the swing. Intraclass correlations and standard error of measurement determined reliability, and pairwise statistics determined between-club differences. Swings with the driver had 7.3° less trunk extension and 4.3° less X-factor at backswing, and 10.5° less trunk flexion and 3.2° less X-factor at ball impact. Older adults portray several differences in lower body kinematics between a six-iron and driver but maintain good to excellent reliability (0.728-0.997) during the swings. Comparisons with previous research also showed senior athletes produce slower club head and ball speeds than younger golfers, and that kinematic differences exist between the populations.

Background Lower extremity sprain and strain injury constitutes a large percentage of lower extremity injuries experienced by soccer players. Yet, very limited data exists on the association between core strength and endurance and this injury. Purpose The purpose of this study was to compare core muscle endurance and hip muscle strength between soccer players who experienced non-contact lower extremity sprain and/or strain injury during their season and those who did not. Additionally, the frequency of injury was correlated with core muscle endurance and hip strength, and endurance was used for predicting the risk for injury. Study design Prospective cohort. Methods Twenty-one (35.59%) athletes experienced non-contact lower extremity sprain and/or strain injury during the season. Fifty-nine male athletes (mean age 20.92 ± 4.08 years, mass 77.34 ± 12.02 kg and height 1.79 ± 0.06m) were tested. Prior to the start of the season, prone-bridge, side-bridge, trunk flexion and horizontal back extension hold times were recorded for endurance assessment and peak hip abductor and external rotator isokinetic torques for strength assessment. Results Prone-bridge and side-bridge hold times were significantly longer in the non-injured players when compared with the times of the injured players (p=0.043 & 0.008 for the prone-bridge and side-bridge, respectively). There were significant negative correlations between the frequency of injury and both prone-bridge (r=-0.324, p=0.007) and side-bridge (r=-0.385, p=0.003) hold times. Logistic regression analysis revealed that side-bridge hold time was a significant predictor of injury (OR=0.956, CI=0.925-0.989). Conclusion Soccer players with non-contact lower extremity sprain and/or strain have less core endurance than non-injured players. Reduced core endurance is associated with increased incidence of injury. Improving side-bridge hold time, specifically, may reduce the risk for injury. Level of evidence 1b.

The purpose of this study is to present a forward kinematics model of the human lumbar spine and to compare the internal loads and trunk flexion extension with existing literature. The forward kinematics model of lumbar spine with 30 DOF was designed using Solidworks and used Matlab to simulate the results for different postures. The forward kinematics model predicted similar trend for trunk flexion extension, compression force, shear forces and moment as described in literature for in vivo studies. The comparison between the proposed model and in vivo measurement showed a pressure difference of less than 15% on the disc L4-L5 for all activities whereas the compression force and moment differed by ~17% on the disc L5-S1. The modeling methodology presented in this thesis provides a more accurate representation of compression forces and moments of the human lumbar spine since the model makes no assumptions regarding muscle force and does not rely on any other software for kinematics data.

Background Previous research has demonstrated elevated activation of the knee flexor muscles in people with knee osteoarthritis. People with this condition have also been observed to walk with increased trunk flexion; this may alter biomechanical loading patterns and change muscle activation profiles. Therefore, the aim of this study was to understand the biomechanical effect of increasing trunk flexion during walking. Methods Kinetic and EMG data were collected from a sample of 20 people with knee osteoarthritis and a sample of 20 healthy matched controls during normal walking. Using a biofeedback protocol, participants were subsequently instructed to walk with a 5° increase in trunk flexion. Sagittal moments, muscle activations and co-contractions were then compared across a window in early stance with a two-way ANOVA test. Results When trunk flexion was increased, there was a corresponding increase in activity of the medial and lateral hamstrings and gastrocnemius muscles as well as a rise in medial co-contraction. This effect was consistent across the two groups. The most pronounced effect was observed for semitendinosus, which showed a dramatic change in activation profile in the healthy group and a 127% increase in activation during early stance. Conclusions This is the first study to demonstrate that increased trunk flexion in people with knee osteoarthritis may explain, to some degree, the elevated knee flexor activity and medial co-contraction which is associated with this disease. These findings motivate further work to understand the therapeutic potential of interventions designed to improve postural alignment.

This study aimed to explore the inter-session reliability of the measures obtained from 2 trunk extension (Biering-Sorensen and Dynamic Extensor Endurance (DEE) tests) and 3 trunk flexion (Ito, Side Bridge and Bench Trunk Curl-Up (BTC) tests) endurance field-based tests in adolescents by sex and age. A total of 208 (males, n = 100; females, n = 108) adolescents (ranging from 12 to 18 years) performed all the field-based tests on 2 separate testing sessions, 7-days apart. The inter-session reliability scores were explored for the total sample and by sex and age groups through relative reliability (intraclass correlation coefficient (ICC)), inter-session differences (systematic bias) and precision of measurements (i.e. absolute reliability) (standard error of measurement expressed as a percentage of the mean score (CVTE) and minimal detectable change (MDC95)). The sensitivity of each test was also assessed through the smallest worthwhile percentage change (SWC). No relevant sex and age groups differences were found for either test-retest reliability or sensitivity in each test, so the grouped scores were considered as generalizable for this cohort of high school-aged adolescents. Most of the trunk endurance measures demonstrated acceptable relative reliability (ICCs ranged from 0.75 to 0.94). However, significant inter-session differences were identified for measures from the DEE and BTC tests. Likewise, the precision of the measurement of each field-based test was poor (CVTE ranged from 11.3 to 24.4%) with the MDC95 revealing that changes higher than 42% for trunk extension endurance tests and 31.4% for trunk flexion endurance tests after an intervention are required to indicate a significant change above measurement error. All tests were sensitive enough to detect moderate to large changes in trunk muscle endurance. Therefore, the findings from this study indicate that only the BTC test demonstrates acceptable inter-session reliability (ICC > 0.9, CVTE ~ 10%, MDC95 ~ 30%) to monitor the changes in trunk endurance scores that may be expected in adolescents after performing an intervention program. The use of supervised familiarization sessions before performing the tests and strong encouragement to perform a maximal effort in each test may be helpful strategies to improve the reliability scores.

Purpose To biomechanically profile force generation connected to the complex role of the trunk in double poling in a representative sample of Para-Nordic sit-skiers. Methods Twelve male World Cup Para-Nordic sit-skiers (sport classes: LW10–12) were skiing on flat snow terrain at submaximal speed of 4.5 m/s (~ 73% maximum speed). 2D video (50 Hz) and pole force analyses (1000 Hz) were performed synchronously, examining angle, force and cycle characteristics to analyse the role of the trunk in generating propulsion. Results LW10–11.5 skiers lost between 21% and 4% propulsive force versus LW12 athletes only due to different geometrics of the trunk and pole angle at an equal axial pole force. While LW10–11 skiers indicated trunk extension or position maintenance during pole thrust, LW11.5–12 skiers showed strong trunk flexion combined with smaller pole angles to the ground. Hence, LW11.5–12 skiers could create larger propulsive forces and therefore greater cycle lengths at lower cycle rates at the same speed. Maximum speed increased from LW10 to LW12 and was significantly correlated to trunk flexion range of motion (r = 0.63) and cycle length (r = 0.59). Trunk flexion ROM showed a significant relationship to the impulse of propulsive force (r = 0.63) and pole angle to the ground (r = − 0.76) (all P Conclusion The impact of impairment on the force production profiles and its physiological-biomechanical consequences need further investigation also in other terrains and at wider spectrums of skiing speeds. The evident problem of low numbers of LW10–11 skiers in World Cup needs creative future solutions for research.

Volleyball players and gymnasts need strength training to achieve their optimum sport performance. The aims of this study were to describe body composition, strength, performance, and characteristics of trunk muscle activation in volleyball players and gymnasts, and to analyze the differences between the sports. The sample consisted of 40 female athletes: rhythmic gymnasts (n = 24, age 13.95 &plusmn, 2.77 years) and volleyball players (n = 16, age 19.81 &plusmn, 5.55 years). Body composition, maximum voluntary contraction (MVC) of isometric tests in an isokinetic dynamometer, McGill core endurance test, and surface electromyography (EMGrms) of the trunk muscle during the McGill test and isometric tests were recorded. Rhythmic gymnasts presented lower body composition values than volleyball players (p &lt, 0.05). The volleyball players presented higher isometric strength than rhythmic gymnasts in terms of MVC in trunk flexion (p &lt, 0.05, d = 1.3) and trunk extension (p &lt, 0.001, d = 1.3). EMGrms from the rhythmic gymnasts were greater for trunk flexor muscles (p &lt, 0.01, d = 0.7) and trunk extensor muscles (p &lt, 0.001, d = 1.3) during McGill endurance tests compared to the volleyball players. In the isometric test, EMGrms from the rhythmic gymnasts were greater for trunk flexor muscles in flexion (p &lt, 0.01, d = 0.9) and extension tests (p &lt, 0.05, d = 0.7). In conclusion, the volleyball players exhibited higher peak strength, despite the fact that the gymnasts showed greater muscle activity during the maximum voluntary contraction.

The objectives of this study were to evaluate the effect of gender and postures of the neck, trunk, and knee on overall postural discomfort, and to classify combined postures into different postural discomfort groups. A total of 95 participants (42 males and 53 females) performed 45 different static postures, which were a combination of 3 neck angles, 5 trunk angles, and 3 knee angles, and rated the perceived postural discomfort. Non-hierarchical K-means cluster analysis was employed to classify the 45 different combined postures into several postural discomfort groups. Postural discomfort was significantly affected by gender and postures of the neck, trunk, and knee (p &lt, 0.001). Three clusters (high, medium, and low discomfort) were identified and the postural discomfort was significantly different between clusters (p &lt, 0.001). The high discomfort group consisted of mostly males with high knee and trunk flexion angles and a moderate neck flexion angle. The low discomfort group was female-dominant with low neck and trunk flexion angles and a moderate knee flexion angle. The different flexibility (stiffness) of the joint motions between genders may affect the gender difference in postural discomfort. The knee and trunk postures were critical to the postural balance, which may affect the perception of whole-body discomfort. This result will be useful for developing and improving postural observation tools.