Effect of the FIFA 11+ injury prevention program in collegiate female football players over three consecutive seasons.

This study aimed to investigate the preventive effects of the FIFA 11+ for one-season and over three consecutive seasons on the injury incidence rates in collegiate female football players in terms of duration of intervention. A total of 763 collegiate female football players from seven teams belonging to Kanto University Women Football Association Division 1 in 2013-2015 seasons were included in the study. At the start of the study, 235 players were assigned to a FIFA 11+ intervention group (four teams, 115 players) and a control group (three teams, 120 players). The intervention period was set to three seasons, and the players were followed up during this period. The one-season effect of the FIFA 11+ was investigated after each season. The effect of continuous intervention was verified in 66 and 62 players from the intervention and control groups who continued the study for all three seasons, respectively. The one-season intervention showed significantly lower total, ankle, knee, sprain, ligament injury, noncontact, moderate and severe injury incidence rates in the intervention group in each season. Regarding the continuous intervention, compared with the first season, the injury incidence rates in lower extremity, ankle, and sprain, decreased in the intervention group by 66.0%, 79.8%, and 82.2%, respectively, in the second season, and by 82.6%, 94.6%, and 93.4%, respectively, in the third season, indicating the persistent effect of the FIFA 11+. In conclusion, the FIFA 11+ is an effective program for lower extremity injury prevention in collegiate female football players, and preventive effects persist with continuation of the program.

Effects of an Injury Prevention Program on Anterior Cruciate Ligament Injury Risk Factors in Adolescent Females at Different Stages of Maturation.

The ideal timing to implement anterior cruciate ligament injury prevention programs with respect to maturation is unclear. The purpose of this study was to investigate the effects of an injury prevention program on knee mechanics in early-, late-, and post-pubertal females. In the study, 178 adolescent female basketball players were assigned to six groups: early-pubertal training, early-pubertal control, late-pubertal training, and late-pubertal control, post-pubertal training, and post-pubertal control. The training groups performed an injury prevention program for six months. Medial knee displacement, knee flexion range of motion, and the probability of high knee abduction moment were assessed before and after the training period. After the six-month training period, medial knee displacement was significantly increased in the early-pubertal control group whereas it was unchanged in the early-pubertal training group. Knee flexion range of motion was significantly decreased in the early-pubertal control group whereas it did not change in the early-pubertal training group. The probability of high knee abduction moment was increased in the early-pubertal control group whereas it was unchanged in the earl-pubertal training group. The probability of high knee abduction moment was also decreased in the post-pubertal training group whereas it did not change in the post-pubertal control group. The program limited the development of high-risk movement patterns associated with maturation in early puberty while improving the knee mechanics in post-pubertal adolescents. Therefore, an injury prevention program should be initiated in early puberty and continue through the post-puberty years.

Comparison of the Position-Matching and Position-Reproducing Tasks to Detect Deficits in Knee Position Sense After Reconstruction of the Anterior Cruciate Ligament.

CONTEXT: Deficits in knee position sense following reconstruction of the anterior cruciate ligament (ACL) can delay an athlete's return to sport participation and increase the risk of reinjury. Deficits in position sense postreconstruction have been evaluated using either a position-reproducing or position-matching task. OBJECTIVE: The aim of our study was to combine both to determine which assessment would be more effective to identify deficits in knee position sense. DESIGN: Longitudinal laboratory-based study. PARTICIPANTS: Eleven athletes (6 men and 5 women; mean age, 20.5 [1.2] y), who had undergone ACL reconstruction with an ipsilateral hamstring autograft, and 12 age-matched controls. INTERVENTIONS: Position sense was evaluated at 6 and 12 months postreconstruction and once for the control group. In addition, peak isokinetic knee extension and flexion strength, at 60°/s and 180°/s, was assessed for the ACL reconstruction group to evaluate possible influences of muscle strength on knee joint position sense. MAIN OUTCOME MEASURES: The variables include the angular differences between the reference limb and indicator limb, and peak torque values of isokinetic knee extension and flexion. RESULTS: Significant matching differences were identified at 6 months postsurgery on the position-matching task, but not at 12 months postsurgery. No significant between-group and within-subject differences were identified on the position-reproducing task. No significant matching errors were identified for the control group. There was no correlation between errors in position sense and maximum isokinetic strength. CONCLUSION: The position-matching task is more sensitive than the position-reproducing task to identify deficits in knee position sense over the first year following ACL reconstruction surgery.

Differences in hamstring activation characteristics between the acceleration and maximum-speed phases of sprinting.

This study aimed to investigate activation characteristics of the biceps femoris long head (BFlh) and semitendinosus (ST) muscles during the acceleration and maximum-speed phases of sprinting. Lower-extremity kinematics and electromyographic (EMG) activities of the BFlh and ST muscles were examined during the acceleration sprint and maximum-speed sprint in 13 male sprinters during an overground sprinting. Differences in hamstring activation during each divided phases and in the hip and knee joint angles and torques at each time point of the sprinting gait cycle were determined between two sprints. During the early stance of the acceleration sprint, the hip extension torque was significantly greater than during the maximum-speed sprint, and the relative EMG activation of the BFlh muscle was significantly higher than that of the ST muscle. During the late stance and terminal mid-swing of maximum-speed sprint, the knee was more extended and a higher knee flexion moment was observed compared to the acceleration sprint, and the ST muscle showed higher activation than that of the BFlh. These results indicate that the functional demands of the medial and lateral hamstring muscles differ between two different sprint performances.

New mouse model of skeletal muscle atrophy using spiral wire immobilization.

INTRODUCTION: Disuse-induced skeletal muscle atrophy is a serious concern; however, there is not an effective mouse model to elucidate the molecular mechanisms. We developed a noninvasive atrophy model in mice. METHODS: After the ankle joints of mice were bandaged into a bilateral plantar flexed position, either bilateral or unilateral hindlimbs were immobilized by wrapping in bonsai steel wire. RESULTS: After 3, 5, or 10 days of immobilization of the hip, knee, and ankle, the weight of the soleus and plantaris muscles decreased significantly in both bilateral and unilateral immobilization. MAFbx/atrogin-1 and MuRF1 mRNA was found to have significantly increased in both muscles, consistent with disuse-induced atrophy. Notably, the procedure did not result in either edema or necrosis in the fixed hindlimbs. CONCLUSIONS: This method allows repeated, direct access to the immobilized muscle, making it a useful procedure for concurrent application and assessment of various therapeutic interventions. Muscle Nerve 54: 788-791, 2016.

Effects of forward trunk lean on hamstring muscle kinematics during sprinting.

This study aimed to investigate the effects of forward trunk lean on hamstring muscle kinematics during sprinting. Eight male sprinters performed maximal-effort sprints in two trunk positions: forward lean and upright. A three-dimensional musculoskeletal model was used to compute the musculotendon lengths and velocity of the biceps femoris long head, semitendinosus, and semimembranosus muscles during the sprinting gait cycle. The musculotendon lengths of all the three hamstring muscles at foot strike and toe-off were significantly greater during the forward trunk lean sprint than during the upright trunk sprint. In addition, a positive peak musculotendon lengthening velocity was observed in the biceps femoris long head and semimembranosus muscles during the late stance phase, and musculotendon lengths at that instant were significantly greater during the forward trunk lean sprint than during the upright trunk sprint. The present study provides significant evidence that a potential for hamstring muscle strain injury involving forward trunk lean sprinting would exist during the stance phase. The results also indicate that the biceps femoris long head and semimembranosus muscles are stretched during forward trunk lean sprinting while contracting eccentrically in the late stance phase; thus, the elongation load on these muscles could be increased.

Mechanics of the muscles crossing the hip joint during sprint running.

We aimed to demonstrate the changes over time in the lengths and forces of the muscles crossing the hip joint during overground sprinting and investigate the relationships between muscle lengths and muscle-tendon unit forces - particularly peak biceps femoris force. We obtained three-dimensional kinematics during 1 running cycle from 8 healthy sprinters sprinting at maximum speed. Muscle lengths and muscle-tendon unit forces were calculated for the iliacus, rectus femoris, gluteus maximus, and biceps femoris muscles of the target leg as well as the contralateral iliacus and rectus femoris. Our results showed that during sprinting, the muscles crossing the hip joint demonstrate a stretch-shortening cycle and 1 or 2 peak forces. The timing of peak biceps femoris force, expressed as a percentage of the running cycle (mean [SD], 80.5 [2.9]%), was synchronous with those of the maximum biceps femoris length (82.8 [1.9]%) and peak forces of the gluteus maximus (83.8 [9.1]%), iliacus (81.1 [5.2]%), and contralateral iliacus (78.5 [5.8]%) and also that of the peak pelvic anterior tilt. The force of the biceps femoris appeared to be influenced by the actions of the muscles crossing the hip joint as well as by the pelvic anterior tilt.

Three-dimensional kinematics of the talocrural and subtalar joints during drop landing.

The bones and soft tissues of the foot act as a shock attenuator and the relative bony motions of the talocrural and subtalar joints are the subject of research interest for their roles in lower extremity pathology. Despite this interest, little information exists on the precise in vivo talocrural and subtalar joint kinematics during dynamic activities. Therefore, the purpose of this study was to quantify the three-dimensional kinematics of the talocrural and subtalar joints during landing by using single-plane fluoroscopic imaging and shape matching techniques. Three-dimensional bone positions for 6 subjects during landing from a 10 cm height were determined by using 3D-2D model-image registration techniques. The primary talocrural joint motion after toe contact was dorsiflexion with rotation ranges averaging 12° ± 7° dorsiflexion, 2° ± 2° eversion, and 3° ± 2° internal rotation. The subtalar joint exhibited similar patterns of increased dorsiflexion, eversion, and external rotation up to 150 ms after landing. The angular changes were 5° ± 3° dorsiflexion, 7° ± 3° eversion, and 6° ± 2° external rotation. This study contributes to the quantitative understanding of the function of the normal talocrural and subtalar joints and can be used for comparison with data obtained from injured feet.

Skeletal muscle adaptation in response to mechanical stress in p130cas-/- mice.

Mammalian skeletal muscles undergo adaptation in response to changes in the functional demands upon them, involving mechanical-stress-induced cellular signaling called "mechanotransduction." We hypothesized that p130Cas, which is reported to act as a mechanosensor that transduces mechanical extension into cellular signaling, plays an important role in maintaining and promoting skeletal muscle adaptation in response to mechanical stress via the p38 MAPK signaling pathway. We demonstrate that muscle-specific p130Cas-/- mice express the contractile proteins normally in skeletal muscle. Furthermore, muscle-specific p130Cas-/- mice show normal mechanical-stress-induced muscle adaptation, including exercise-induced IIb-to-IIa muscle fiber type transformation and hypertrophy. Finally, we provide evidence that exercise-induced p38 MAPK signaling is not impaired by the muscle-specific deletion of p130Cas. We conclude that p130Cas plays a limited role in mechanical-stress-induced skeletal muscle adaptation.

Pelvic rotation and lower extremity motion with two different front foot directions in the tennis backhand groundstroke.

When a tennis player steps forward to hit a backhand groundstroke in closed stance, modifying the direction of the front foot relative to the net may reduce the risk of ankle injury and increase performance. This study evaluated the relationship between pelvic rotation and lower extremity movement during the backhand groundstroke when players stepped with toes parallel to the net (Level) or with toes pointed towards the net (Net). High school competitive tennis players (eleven males and seven females, 16.8 ± 0.8 years, all right- handed) performed tennis court tests comprising five maximum speed directional runs to the court intersection line to hit an imaginary ball with forehand or backhand swings. The final backhand groundstroke for each player at the backcourt baseline was analyzed. Pelvic rotation and lower extremity motion were quantified using 3D video analysis from frontal and sagittal plane camera views reconstructed to 3D using DLT methods. Plantar flexion of ankle and supination of the front foot were displayed for both Net and Level groups during the late phase of the front foot step. The timings of the peak pelvis rotational velocity and peak pelvis rotational acceleration showed different pattern for Net and Level groups. The peak timing of the pelvis rotational velocity of the Level group occurred during the late phase of the step, suggesting an increase in the risk of inversion ankle sprain and a decrease in stroke power compared to the Net group. Key PointsRegarding the movement of the forefoot, the Net group and the Level group showed a pattern of supination-pronation-supination during the front stepping foot contact phase (FSFCP). However, the Level group showed only supination of various degrees during FSFCP.For the Net group, the maximum angular velocity of pelvis occurred in the early phase of FSFCP before impact; however, for the Level group, the maximum angular velocity of pelvis occurred in the latter phase of FSFCP after impact.The Level group players showed a potentially higher risk of inversion ankle sprain during the latter stage of FSFCP as pelvic rotation reached maximum angular velocity.The Net group may have a more effective kinetic chain during backhand groundstrokes, which ultimately enhances performance.

Relationship between muscle volume and muscle torque of the hamstrings after anterior cruciate ligament lesion.

PURPOSE: This study was conducted to identify factors other than morphological muscle strength factors that affect injured and uninjured sides of knee flexors with anterior cruciate ligament (ACL) lesions. METHODS: The study population consisted of 22 patients with ACL lesions. Their hamstring muscle volume was measured on MRI, and muscle torque per muscle volume was calculated as the peak torque of knee flexion divided by hamstring muscle volume. RESULTS: The mean muscle torque per unit volume of hamstrings in patients with ACL rupture was 0.09 ± 0.02 Nm/cm(3) at 60°/s and 0.08 ± 0.01 Nm/cm(3) at 180°/s on the injured side, and 0.11 ± 0.02 Nm/cm(3) at 60°/s and 0.08 ± 0.01 Nm/cm(3) at 180°/s on the uninjured side. The mean muscle torque per unit volume of hamstrings in control subjects was 0.11 ± 0.02 Nm/cm(3) at 60°/s and 0.08 ± 0.03 Nm/cm(3) at 180°/s. One-factor ANOVA analysis found no significant differences between the three groups at either flexion velocity. CONCLUSIONS: Neurological dysfunction does not appear to exist in knee flexor muscles after ACL injury, unlike the quadriceps. Since the mechanism of muscle weakness will differ depending on the muscle, it is important for clinicians to take this discrepancy into consideration. LEVEL OF EVIDENCE: II.

Acupuncture ameliorated skeletal muscle atrophy induced by hindlimb suspension in mice.

Preventing skeletal muscle atrophy is critical for maintaining quality of life, but it is often a challenging goal for the elderly and patients with severe conditions. We hypothesized that acupuncture in place of exercise training is an alternative non-pharmacological intervention that can help to prevent muscle atrophy. To elucidate the effects of acupuncture on skeletal muscle atrophy caused by hindlimb suspension (HS), we performed acupuncture on mice according to two different methods: acupuncture with electrical stimulation (EA: electroacupuncture) and without electrical stimulation (MA: manual acupuncture). A needle was retained in the gastrocnemius muscle for 30 min every day for 2 weeks in the EA and MA groups. In the EA group, 30 min of repetitive electrical stimulation (1 Hz, 1 ms pulse width, 6.5 mA intensity) was also applied. HS significantly reduced muscle mass and the cross-sectional area of the soleus muscles. This HS-induced reduction was significantly improved in the EA group, although the level of improvement remained insufficient when compared with the control group. We found that the mRNA expression levels of atrogin-1 and MuRF1, which play a principal role in muscle-specific degradation as E3 ubiquitin ligases, were significantly increased in the HS group compared to the control group. EA and MA reduced the HS-induced upregulation of atrogin-1 (p<0.01 in EA and MA) and MuRF1 (p<0.01 in EA) mRNAs. We also found that the expression levels of PI3K, Akt1, TRPV4, adenosine A1 receptor, myostatin, and SIRT1 mRNAs tended to be increased by HS. EA and MA further increased the HS-induced upregulation of Akt1 (p<0.05 in MA) and TRPV4 (p<0.05 in MA) mRNAs. We concluded that acupuncture partially prevented skeletal muscle atrophy. This effect might be due to an increase in protein synthesis and a decrease in protein degradation.

Strenuous resistance exercise effects on magnetic resonance diffusion parameters and muscle-tendon function in human skeletal muscle.

PURPOSE: To assess the effects of strenuous exercise on magnetic resonance diffusion parameters and muscle-tendon complex function in skeletal muscle. MATERIALS AND METHODS: Six men performed ankle plantar flexion exercises with eccentric contraction. The fractional anisotropy (FA), λ(1) , λ(2) , λ(3) , mean diffusivity (MD), and T(2) values in the triceps surae muscles were measured by magnetic resonance diffusion tensor and spin-echo imaging. Passive torque of plantar flexors, maximal voluntary isometric plantar flexion torques (MVIP), and Achilles tendon stiffness during MVIP were measured by combined ultrasonography and dynamometry. Plasma creatine kinase and muscle soreness were also assessed. These parameters were measured before and 1-8 days postexercise. RESULTS: The medial gastrocnemius exhibited significantly decreased FA 2-5 days after, increased λ(2) 3 days after, and increased λ(3) 2 and 3 days after exercise. This muscle also showed significantly increased MD and T(2) values 3 days postexercise. MVIP significantly decreased 2 and 3 days postexercise, while passive torque significantly increased 2 days postexercise. Creatine kinase and muscle soreness increased 3-5 days and 1-5 days postexercise, respectively. CONCLUSION: Exercise-induced muscle damage manifested as significant changes in muscle diffusion parameters with muscle-tendon complex dysfunction and delayed-onset muscle soreness.

Alterations in intramuscular water movement associated with mechanical changes in human skeletal muscle fibers: an evaluation using magnetic resonance diffusion-weighted imaging and B-mode ultrasonography.

BACKGROUND: Intramuscular water movement is expected to be affected by the mechanical changes of the muscle fibers. However, the effect of changes in fiber length (FL) and pennation angle (PA) on the water movement has not been sufficiently investigated in human skeletal muscles. PURPOSE: To determine the relationship between intramuscular water movement and the mechanical changes in human muscle fibers. MATERIAL AND METHODS: Axial magnetic resonance diffusion-weighted images of the right leg (eight men) were taken using a 1.5-Tesla device with the ankle joint maximally dorsiflexed and maximally plantar flexed. The apparent diffusion coefficient (ADC) values of both the dorsiflexors (the superficial and deep parts of the tibialis anterior) and the plantar flexors (medial gastrocnemius and soleus) were calculated along three orthogonal axes (S-I: superior-to-inferior, A-P: anterior-to-posterior, and R-L: right-to-left). FL and PA of both muscle groups were also calculated from longitudinal B-mode ultrasound images with the ankle joint maximally dorsiflexed and plantar flexed. RESULTS: There was a significant increase in the ADC in superficial (P < 0.05) and deep (P < 0.05) parts of the dorsiflexors in the S-I direction when the ankle was plantar flexed and in the A-P and R-L directions when the ankle was dorsiflexed (P < 0.05). The plantar flexors showed significantly elevated ADC in the S-I direction when the ankle was dorsiflexed (P < 0.05), and in the A-P and R-L directions when the ankle was plantar flexed (P < 0.05). The dorsiflexors also showed significantly increased PA and decreased FL values when the ankle was dorsiflexed (P < 0.05). The plantar flexors displayed similar morphological changes when the ankle was plantar flexed (P < 0.05). CONCLUSION: Water diffusion is affected by structural changes in the long axis of the muscle fibers, namely the changes in PA and FL.

Relationship between three-dimensional kinematics of knee and trunk motion during shuttle run cutting.

Female athletes are considered to exhibit knee and trunk motion that is characteristic of anterior cruciate ligament (ACL) injury. The aim of this study was to examine the in vivo motion of the trunk and knee during a cutting manoeuvre and determine the relationship between them. All participants (10 male and 10 female college athletes) performed a shuttle run cutting task with the left limb. Trunk inclination (forward and lateral) and knee joint angles (flexion/extension, abduction/adduction, and internal/external tibial rotation) were calculated. Differences between the sexes and associations between knee motion and trunk inclination were examined. An increase in trunk forward inclination was strongly correlated with an increase in knee flexion angle and moderately correlated with a decrease in the excursion of internal tibial rotation. An increase in right trunk lateral inclination was moderately correlated with an increase in excursion of internal tibial rotation. The results also showed differences between the sexes in trunk forward inclination, lateral inclination, and knee flexion angle, but no such differences in knee abduction or internal tibial rotation. Trunk inclination is related to knee flexion and excursion of internal tibial rotation. Female athletes demonstrate a low trunk forward inclination and knee flexion angle, a posture that resembles that of ACL injury.

Relationship between quadriceps femoris muscle volume and muscle torque after anterior cruciate ligament rupture.

PURPOSE: The purpose of this study was to obtain evidence to support the hypothesis that motor unit recruitment is reduced in the quadriceps femoris (QF) of patients with ACL rupture. METHODS: We compared muscle torque per unit volume in the QF from injured and uninjured sides to normal subjects. If high-threshold motor unit recruitment is reduced in patients with ACL rupture, this reduction will theoretically lead to a reduction in muscle torque per unit volume compared to the control group. The subjects included 22 patients with ACL rupture and 22 subjects with no history of knee injury. To identify the muscle torque per unit volume, the isokinetic peak torque was divided by QF volume which was obtained by MRI. RESULTS: Tests revealed that the mean muscle torque per unit volume of the uninjured and injured sides was significantly lower than those of the control group. CONCLUSION: This study demonstrated that the values of the muscle torque per unit volume of both injured and uninjured sides of patients with ACL rupture were significantly lower than those of the control group, thereby providing indirect evidence of the hindrance of motor unit recruitment in these patients. The results of the present study also indicate that there may be bilateral QF weakness in patients with ACL rupture. Since persistent QF weakness is a significant barrier to effective rehabilitation in patients with ACL injuries, a better understanding of the underlying mechanisms will allow clinicians and scientists to develop more effective therapeutic strategies for patient rehabilitation.

Hamstring functions during hip-extension exercise assessed with electromyography and magnetic resonance imaging.

The purpose of this study was to compare the recruitment patterns in hamstring muscles during hip extension exercise by electromyography (EMG) and muscle functional magnetic resonance imaging (mfMRI). Six male volunteers performed 5 sets of 10 repetitions of the hip extension exercise. Electromyography (EMG) activity during the exercise was recorded for the biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) muscles; mfMRI T2 values and cross-sectional areas (CSAs) of the same muscles were measured at rest, immediately after, 2 and 7 days after the exercise. The study found that EMG of the BFlh and SM were significantly higher than that of the ST. Immediately after the exercise, the T2 value and CSA changes in the SM showed a significant increase. It was concluded that the BFlh and SM were selectively recruited during the hip extension exercise.

The Relationship between Performance and Trunk Movement During Change of Direction.

The purpose of this study was to obtain the trunk kinematics data during a change-of-direction task and to determine the relationship between trunk kinematics and the change-of-direction performance. The design of this investigation was a descriptive laboratory study. Twelve healthy male collegiate soccer players (age: 21.3 ± 1.0 yrs, body mass: 67. 7 ± 6.7 kg, and height: 1.75 ± 0.05 m) participated in this study. Participants performed a shuttle run cutting task with a 180 degree pivot as quickly as possible. The shuttle run cutting time, ground contact time during a change-of-direction, and trunk inclination angle were measured. The shuttle run cutting time tends to correlate positively with ground contact time. During the change- of-direction task, the trunk forward inclination angle gradually increased during the first 50% of the stance phase and decreased subsequently whereas the trunk flexed, maintaining a left inclination during the first 40% of the stance phase and changing exponentially in the opposite direction. Forward angular displacement of the trunk between foot-contact and maximum trunk inclination correlated positively with the shuttle run cutting time (r = 0.61, p < 0.05) and ground contact time (r = 0.65, p < 0.05). These findings suggest that the change-of-direction performance could be related to the small angular displacement of the trunk during a change of direction. Moreover, it was considered that there might be optimal inclination angles related to change-of-direction performance. Therefore, coaches in field sports should check body posture and trunk movements during changes of direction. Key pointsSmall forward angular displacement of the trunk during a direction change is related to the change-of-direction performance.Trunk stability during a change of direction is an important factor in the change-of-direction performance.There might be a range of optimal angles of trunk inclination during a change of direction.Coaches in field sports should check the body posture and trunk movement of players when they require a change of direction or when they participate in sport-specific change-of-direction training.

Differences in the electromyographic activity of the hamstring muscles during maximal eccentric knee flexion.

This study investigated the effects of the knee joint angle and angular velocity on hamstring muscles' activation patterns during maximum eccentric knee flexion contractions. Ten healthy young males (23.4 +/- 1.3 years) performed eccentric knee flexion at constant velocities of 10, 60, 180, and 300 deg/s in random order. The eccentric knee flexion torque and the surface electromyographic (EMG) activity of the biceps femoris (BF), semitendinosus (ST), and semimembranosus (SM) muscles were measured. The results of torque during 10 deg/s were lower than the faster velocities. No significant change was found in eccentric torque output and the EMG amplitude with change in the faster test velocities, although those values showed a decreasing tendency as the knee approached extension. Furthermore, the EMG amplitude of the BF decreased significantly as the knee approached extension, although the EMG activity of the ST and SM remained constant. These results suggest that the neural inhibitory mechanism might be involved in decreasing in maximal voluntary force and hamstring muscles activation toward the knee extension during high-velocity eccentric movement and therefore subjects have difficulties to maintain high eccentric force level throughout the motion. Moreover, the possible mechanism reducing the BF muscle activation as the knee approaches extension was architectural differences in the hamstring muscles, which might reflect each muscle's function.

Effects of different cooling treatments on water diffusion, microcirculation, and water content within exercised muscles: evaluation by magnetic resonance T2-weighted and diffusion-weighted imaging.

In this study, we determined the effects of different cooling treatments on exercised muscles. Seven adults underwent four post-exercise treatments (20-min ice-bag application, 60-min gel-pack application at 10 degrees C and 17 degrees C, and non-cooling treatment) with at least 1 week between treatments. Magnetic resonance diffusion- and T2-weighted images were obtained to calculate the apparent diffusion coefficients (apparent diffusion coefficient 1, which reflects intramuscular water diffusion and microcirculation, and apparent diffusion coefficient 2, which is approximately equal to the true diffusion coefficient that excludes as much of the effect of intramuscular microcirculation as possible) and the T2 values (intramuscular water content level) of the ankle dorsiflexors, respectively, before and after ankle dorsiflexion exercise and after post-exercise treatment. The T2 values increased significantly after exercise and returned to pre-exercise values after each treatment; no significant differences were observed among the four post-exercise treatments. Both apparent diffusion coefficients also increased significantly after exercise and decreased significantly after the three cooling treatments; no significant difference was detected among the three cooling treatments. Local cooling suppresses both water diffusion and microcirculation within exercised muscles. Moreover, although the treatment time was longer, adequate cooling effects could be achieved using the gel-pack applications at relatively mild cooling temperatures.