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This study aimed to clarify the relationship between knee flexor strength and hamstring muscle morphology after anterior cruciate ligament ( ACL) reconstruction using the semitendinosus ( ST) tendon and to determine the causative factors of decreased knee flexor muscle strength. Fourteen male and ten female patients who resumed sports activities after surgery participated in the experiment. Isometric knee flexion torque was measured at 30°, 45°, 60°, 90°, and 105° of knee flexion. Magnetic resonance imaging ( MRI) was used to calculate ST muscle length and hamstring muscle volume, and to confirm the status of ST tendon regeneration. The correlation between the MRI findings and flexor strength was analyzed. Regenerated ST tendon was confirmed in 21 of the 24 patients, but muscle volume (87.6%) and muscle length (74.5%) of the ST in the operated limb were significantly smaller than those in the normal limb. The percentage of the knee flexion torque of the operated limb compared with that of the normal was apparently lower at 105° (69.1%) and 90° (68.6%) than at 60° (84.4%). Tendon regeneration, ST muscle shortening, and ST muscle atrophy correlated with decreased knee flexion torque. These results indicated that preserving the morphology of the ST muscle-tendon complex is important. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate whether the effect of Nordic Hamstrings (NH) training, a partner exercise focusing on the eccentric phase for the prevention of hamstring strain differed between individual hamstrings [biceps femoris muscle long head (BF1) and short head (BFs), semimembranosus muscle (SM), and semitendinosus muscle (ST)]. Eight male volunteers performed six weeks of NH training. Load was gradually increased by a number of sets and exercising time to resist a forward--falling motion using hamstrings. To evaluate the training effect, the maximal isometric, concentric and eccentric knee flexion torques and the EMG activities of the hamstrings during isometric knee flexions were measured before, after the three weeks and after the six weeks training period. Moreover, the muscle volume of the hamstrings and the Gracilis muscle (G) were measured before and after the training period. There was a significant increase in eccentric knee flexion torque at 30°/sec, as well as an increase in isometric knee flexion torque at 15°, 30°, 45°, 60°, and 75°. Only in the ST did the EMG value significantly increase at 15° after the first three weeks of the training. Muscle volume of the ST, BFs and G increased significantly. These results showed that the effect of NH training for six weeks was different for each hamstring and the training had a marked effect for the ST. [ABSTRACT FROM AUTHOR]

In an athletic event appropriate shoes enhance performance and prevent injury to athletes. The Japan Cheerleading Association makes a rule of wearing the standard shoes at tournaments. The standard shoes have only one width size for each length size. We measured the foot length (FL) and width (FW) of 35 female collegiate cheerleaders and compared them with their chosen shoe size. Cheerleaders were divided into three positions (base : n = 16, spot : n = 9, and top : n = 10). The ratio of FW to FL significantly correlated with the difference between shoe size and FL (r = 0.544, p < 0.021). That is, the larger a subject's FW was, the greater the difference between her shoe size and FL. This relationship was significant in base and spot cheerleaders and was not significant in top cheerleaders. These results suggest that cheerleaders choose their shoes to fit their FW. In other words, cheerleaders place more importance on FW than FL their choice of standard shoes. In stunts, the falling over of a top cheerleader results in extremely serious injury, such as cervical spinal cord injury and acute death. The shoes of top cheerleaders, whose feet are grasped by base and spot cheerleaders, must fit closely to prevent falling over. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effect of daily exercise on skeletal muscle function, size, and quality in young women. Twenty-six young women participated in this study, categorized into daily exercise and non-exercise groups. The exercise group had performed exercise or training three times a week for more than six months. Knee extension and flexion, plantar flexion, and dorsiflexion peak torques were measured for muscle function. B-mode ultrasound images were taken from the thigh and calf, and muscle thickness and echo intensity were measured in the vastus lateralis and medial gastrocnemius. Shear modulus at different joint angles of the knee (0° [full extended], 40°, and 90°) and ankle (40 °plantarflexion, 0° [neutral], and 10° dorsiflexion) was measured from the vastus lateralis and medial gastrocnemius to determine muscle stiffness. Peak torque and echo intensity did not significantly differ between the exercise and non-exercise groups. Shear modulus in the medial gastrocnemius at 10° dorsiflexion was significantly lower in the exercise group compared with the non-exercise group (34.2±7.7 vs. 46.5±13.1 kPa, P <0.05). These results suggest that daily exercise and training could affect muscle stiffness, but do not lead to an increase in muscle function., Competing Interests: The authors declare that they have no conflict of interest., (Thieme. All rights reserved.)

Background/purpose: This study aimed to evaluate how a two-week program using the in-phase mode of a balance adjustment system (the BASYS) affected postural control in participants with chronic ankle instability (CAI). It was hypothesized that the in-phase mode on the BASYS would lead to improved postural control compared with training on a balance disc., Study Design: Randomized control trial., Methods: Twenty participants with CAI were recruited. The participants were divided into two intervention groups: the BASYS (n = 10) and Balance Disc (BD; cushion type, n = 10). All participants underwent six supervised training sessions over a two-week period. Static postural control during single leg standing with closed eyes was assessed for the CAI limb. We collected COP data while participants balanced on the BASYS. The test was performed for 30 sec, and the total trajectory length and 95% ellipse area were calculated. In the assessment of dynamic postural stability, Y-Balance tests-anterior, posteromedial, and posterolateral directions were measured on the CAI limb for all participants and normalized to the individual's leg length. Participants were recorded at three instances: pretraining (Pre), post-training 1 (Post1: after the first training), and post-training 2 (Post2: after the last training)., Results: There was an effect on time in the COP total trajectory length of the BASYS group, which was significantly decreased for Post 1 and Post 2 than for the Pre (p = 0.001, 0.0001). Group differences and time-by-group interactions were not observed for either of the Y-balance test reach distances., Conclusions: The study's primary finding was that two weeks of intervention in the in-phase mode on the BASYS improved static postural control in participants with CAI., Level of Evidence: Level Ⅰ, randomized control trial., Competing Interests: The authors have no competing interests to disclose.

Adipokines secreted from adipose tissue, such as adiponectin and leptin, enhance skeletal muscle metabolism. Animal studies have shown that adipokine knockout leads to a reduction in muscle function. Muscle function is determined by muscle size and quality; therefore, it is speculated that lower adipokine levels affect skeletal muscle size and quality, eventually leading to lower muscle function. This study aimed to investigate the relationship between adipokines and skeletal muscle morphology and function in young individuals. A total of 21 young women participated in this study. Adiponectin and leptin levels were analyzed using fasting blood samples from all participants. B-mode ultrasound images of the thigh and calf were obtained, and the muscle thickness and echo intensity were measured in the vastus lateralis (VL) and medial gastrocnemius (MG). The shear modulus was measured from the VL and MG using shear wave elastography. Knee extension and plantar flexion peak torques were measured as muscle functions. Adiponectin and leptin were not related to echo intensity, shear modulus, and muscle thickness in the VL and MG (r s = -0.26-0.37, P > .05). Furthermore, no relationship was observed between adiponectin, leptin, knee extension, and dorsiflexion peak torque (r s = -0.28-0.41, P > .05). These negative results suggest that adiponectin and leptin levels in young women are not associated with muscle size and quality, nor are they related to muscle function., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Endocrine Society.)

Background: Pole vaulting involves trunk flexion, extension, and rotation, which may place the lumbar spine under stress. Repeated pole vaulting may cause lumbar disc degeneration (DD) and lumbar spondylolysis (LS); however, this phenomenon is yet to be established., Objective: This study aimed to determine the difference in the maximum joint angles of the shoulder, hip, and trunk during pole vaulting between male pole vaulters with and without lumbar DD or LS., Methods: This retrospective study included 17 male pole vaulters. Four high-speed cameras were used to record the pole vaulters at 240 Hz. Radiography and magnetic resonance imaging were used to examine the lumbar spine in all athletes. Differences in the data between two sets of groups were analyzed using the unpaired t-test or the Mann-Whitney U test., Results: There was a significant difference in the maximum joint angle of hip flexion between pole vaulters with and without lumbar DD (p= 0.03)., Conclusion: Pole vaulters with lumbar DD may use lumbar flexion instead of hip flexion during the rock-back movement. Moreover, LS may occur due to repeated failed vaulting. Therefore, trunk stability and functional movements should be prioritized to prevent organic changes in the lower back.

Background: The lower back is the most common injury location in pole vaulters, but the prevalence of lumbar spondylolysis and intervertebral disc degeneration is not known., Objective: This study aimed to determine the prevalence of lumbar spondylolysis and intervertebral disc degeneration in pole vaulters., Methods: This cross-sectional study was conducted in the Tokai area of Japan and included 21 pole vaulters (mean ± standard deviation [range]: age, 22.2 ± 3.2 [18-28] years; height, 172.2 ± 4.7 [165.0-182.0] cm; body weight, 67.6 ± 7.3 [54.0- 80.0] kg). The majority of pole vaulters were collegiate athletes. We performed anterior, lateral, and oblique radiography at 45∘ and magnetic resonance imaging in the sagittal and coronal planes of the lumbar spine. The evaluation was performed independently of whether the athletes had lower back pain (LBP). Moreover, we investigated the duration of pole-vaulting experience and history and current presence of LBP using a questionnaire., Results: The prevalence of lumbar spondylolysis and intervertebral disc degeneration was 28.6% (6/21) and 38.1% (8/21), respectively. Herniation was found in six discs in four vaulters (19.0%). All athletes had a history of LBP. The prevalence of lumbar spondylolysis was high (28.6%)., Conclusions: Sport-specific movements performed by pole vaulters may be a risk factor for lumbar spondylolysis.

Background: Pole vaulters and decathletes frequently experience several types of injuries to their lower back, often resulting in mechanical low back pain (LBP). However, the risk factors for the occurrence of LBP in these athletes have not been defined., Purpose: To determine the physical factors that relate to LBP occurrence for collegiate pole vaulters and decathletes., Study Design: Cohort study; Level of evidence, 2., Methods: We observed 31 pole vaulters and decathletes for 1 year. At the start of the observation period, isokinetic flexion and extension muscle strength of the knee and hip joints were recorded along with active and passive range of motion (ROM) and muscle tightness. Participants were then divided into 2 groups using the median value of each measurement: those below the median (low group) and those above the median (high group). The log-rank test was used to compare LBP occurrence between the low group and high group for all measurements. Multivariate regression analyses were thereafter applied using the Cox proportional hazards regression., Results: Log-rank tests revealed a statistically significant change in the survival curve for the occurrence of LBP in the participants with chronic LBP ( P = .037), the low group for hip flexion peak torque per body weight on the non-takeoff leg ( P = .047), and the low group for passive hip flexion angle on both legs (takeoff leg: P = .034; non-takeoff leg: P = .023). In addition, log-rank tests revealed a statistically significant change in the survival curve for the occurrence of LBP in the low group for passive hip extension angle on the takeoff leg only for the participants without chronic LBP ( P = .014)., Conclusion: It may be necessary to acquire sufficient ROM and hip flexion to prevent LBP occurrence in pole vaulters and decathletes., Competing Interests: The authors have declared that there are no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto., (© The Author(s) 2021.)

Background: Athletes participating in track and field jumping events (long jump, triple jump, high jump, and pole vault) are exposed to ground-reaction forces on the takeoff leg that are several times their body weight. This can cause injuries specific to such activities., Purpose: To determine the incidence of injuries in collegiate jumpers using the guidelines set forth by a 2014 consensus statement on injury surveillance during track and field events., Study Design: Descriptive epidemiology study., Methods: A total of 51 jumpers between April 2016 and March 2017 and 54 jumpers between April 2017 and March 2018 participated in this study. All athletes were from a single college in Japan. Baseline information on athletes participating in the long jump, triple jump, high jump, and pole vault was collected at study enrollment. Practice and competition exposures were reported by the team trainer. Injury incidence was calculated as the number of injuries per 1000 athlete-exposures (AEs)., Results: A total of 147 injuries were reported among 16,998 exposures (8.65 injuries per 1000 AEs). The most common injury locations were the posterior thigh and lateral ankle (17.0%), followed by the posterior foot or toe (12.9%); the most frequent type of injury was strain/muscle rupture/tear (21.1%). The most common injury for long jumpers was ankle sprain (23.3%); for high jumpers, flexor hallucis longus tendinosis (15.8%); and for pole vaulters, hamstring strain (13.2%)., Conclusion: The overall characteristics are different for each event; therefore, injuries for each event need to be investigated., Competing Interests: The authors declared that there are no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto., (© The Author(s) 2021.)

Background: The low back is the most common injury location in pole vaulters, and low back pain (LBP) can easily become chronic. Therefore, knowing the physical characteristics of athletes experiencing repeated LBP may be beneficial for recovery and injury prevention., Purpose: The purpose of this study was to describe and analyze the physical characteristics of pole vaulters with chronic LBP., Study Design: A cross-sectional study., Methods: Twenty male pole vaulters participated in this study. A questionnaire was used to garner descriptive and personal data, including personal best performance in the pole vault. Additionally, the following physical characteristics were measured: 1) isokinetic muscle strength of hip and knee flexors and extensors, 2) active/passive range of motion and muscle flexibility in multiple joints and regions, 3) performance on the Functional Movement Screen™ (FMS™) and 4) spinal column alignment. Subjects were categorized using the questionnaire and divided into two groups, one with and one without chronic LBP., Results: The personal best performance and angle on the active straight leg raise test (SLR) were significantly lower and smaller, respectively, in the chronic LBP group than in the non-chronic LBP group. Additionally, the difference between the passive SLR angle and active SLR angle (ΔSLR) was significantly larger in the chronic LBP group than in the non-chronic LBP group. Those with chronic LBP had were more likely to have a FMS™ composite score ≤14., Conclusion: The active SLR angle and ΔSLR were significantly smaller and larger, respectively, in the chronic LBP group than in the non-chronic LBP group. This may be because of the poor stability of trunk or incompetence of the kinetic chain required for raising the lower limbs. The chronic LBP group had a significantly higher probability of having an FMS™ composite score of ≤14. it may be important to examine the active straight leg raise (vs. passive only), and fundamental movements as screened by the FMS ™ in pole vaulters., Level of Evidence: 2b., (© 2020 by the Sports Physical Therapy Section.)

In this study, we aimed to clarify the characteristics of neuromuscular function, kinetics, and kinematics of the lower extremity during sprinting in track and field athletes with a history of strain injury. Ten male college sprinters with a history of unilateral hamstring injury performed maximum effort sprint on an athletic track. The electromyographic (EMG) activity of the long head of the biceps femoris (BFlh) and gluteus maximus (Gmax) muscles and three-dimensional kinematic data were recorded. Bilateral comparisons were performed for the EMG activities, pelvic anterior tilt angle, hip and knee joint angles and torques, and the musculotendon length of BFlh. The activity of BFlh in the previously injured limb was significantly lower than that in the uninjured limb during the late-swing phase of sprinting ( p < 0.05). However, the EMG activity of Gmax was not significantly different between the previously injured and uninjured limbs. Furthermore, during the late-swing phase, a significantly more flexed knee angle ( p < 0.05) and a decrease in BFlh muscle length ( p < 0.05) were noted in the injured limb. It was concluded that previously injured hamstring muscles demonstrate functional deficits during the late swing phase of sprinting in comparison with the uninjured contralateral muscles.

Hamstring strain injury is a multifactorial and complex problem involving interactions among various factors. Information about risk factors for this injury is inconsistent among studies because the strong effects of confounding factors and injury situations are often ignored. We investigated the relationship between hamstring strain induced by high-speed running and intrinsic risk factors, including hip muscle morphology and function, by excluding the influences of confounding factors. Sixty-one male track and field athletes (age, 19.6 ± 1.1 years; 95% confidence interval, 19.3-19.9) who often performed high-speed running were monitored throughout one season. Before the season, we measured hip and knee strength, muscle thickness of the gluteus maximus and biceps femoris, and hip and knee joint range of motion (ROM). We also obtained information about each athlete's history of hamstring injury by questionnaire. Eighteen athletes sustained hamstring strain injuries induced by high-speed running. Eighteen uninjured athletes who had the same profile of confounding factors as the injured athletes were selected as controls. Previously injured athletes had a significantly higher injury rate than uninjured athletes (p < .05; odds ratio, 2.85). No other measurements had a significant relationship with the occurrence of injury. However, passive hip ROM (flexion and extension) tended to be larger in the injured than control group. A history of hamstring strain was a strong risk factor for hamstring strain injury, and it may affect other factors. Therefore, the risk factors for hamstring strain injury should be investigated by eliminating the impact of a history of hamstring strain.

Purpose/background: Female adolescents change their landing mechanics during puberty. It is unknown whether implementation of anterior cruciate ligament (ACL) injury prevention training reduces the loss of knee control in female athletes during puberty. The purpose of this study was to evaluate the effect of injury prevention training on dynamic knee alignment in female basketball players specifically when the knee mechanics were changing during puberty., Methods: Sixty female junior high school basketball players participated and were divided into two groups: a training group (n = 32) and a control group (n = 28). The training group underwent an injury prevention program for 6 months, whereas the control group maintained a regular training routine. The knee valgus motion and knee flexion range of motion during a drop vertical jump were measured before and after the training period. The probability of a high knee abduction moment (pKAM) was also evaluated using an ACL injury prediction algorithm., Results: The knee valgus motion was significantly increased in the control group (p < 0.001), whereas it did not change in the training group (p = 0.64). Similarly, the knee flexion range of motion was significantly decreased in the control group (p < 0.001), whereas it was not changed in the training group (p = 0.55). The pKAM was significantly increased in the control group (p < 0.001), but not in the training group (p = 0.06)., Conclusions: Implementation of injury prevention training was effective in limiting the loss of knee control in female athletes during puberty. Lowering the risk of ACL injury might be possible in this population., Level of Evidence: 2b.

The aim of this study was to test whether anticipation of upcoming head blow stimuli, which elicit reflex responses in the neck muscle, makes the reflex responses greater or not. In nine healthy subjects the reflex responses were elicited in the sternocleidomastoid (SCM) muscle in the eyes-open (EO) and eyes-closed (EC) conditions, which corresponded to the predictable and unpredictable conditions, respectively. The subjects were instructed not to resist the perturbations after the impact. The results demonstrated that the reflex response of the SCM muscle was significantly smaller in the predictable EO condition than in the unpredictable EC condition (P < 0.05), although no significant differences were observed in either the background EMG activities or the head accelerations. Further, this effect of anticipation was observed only in the later reflex EMG component, which most probably mediated the stretch reflex pathway. In contrast, no significant difference was observed in the early component, which was presumed to be the vestibular-collic reflex. The reduced stretch reflex response was suggested to be functionally relevant to the task requirement, i.e., to let the neck extension movement occur, and not to resist after the impact of the head blow. It was concluded that the anticipation has an effect on reducing the stretch reflex responses in the neck muscle, but does not have any effect on the presumed vestibular-collic reflex under the present experimental paradigm. It is suggested that the gain of the stretch reflex pathway is modulated by anticipatory information of upcoming mechanical event.