Ayako Higashihara

Differences in activation properties of the hamstring muscles during overground sprinting

The purpose of this study was to quantify activation of the biceps femoris (BF) and medial hamstring (MH) during overground sprinting. Lower-extremity kinematics and electromyography (EMG) of the BF and MH were recorded in 13 male sprinters performing overground sprinting at maximum effort. Mean EMG activity was calculated in the early stance, late stance, mid-swing, and late-swing phases. Activation of the BF was significantly greater during the early stance phase than the late stance phase (p<0.01). Activation of the BF muscle was significantly lower during the first half of the mid-swing phase than the other phases (p<0.05). The MH had significantly greater EMG activation relative to its recorded maximum values compared to that for the BF during the late stance (p<0.05) and mid-swing (p<0.01) phases. These results indicate that the BF shows high activation before and after foot contact, while the MH shows high activation during the late stance and mid-swing phases. We concluded that the activation properties of the BF and MH muscles differ within the sprinting gait cycle.

Relationship between the peak time of hamstring stretch and activation during sprinting

Abstract The purpose of this study was to investigate the time series relationships between the peak musculotendon length and electromyography (EMG) activation during overground sprinting to clarify the risk of muscle strain injury incidence in each hamstring muscle. Full-body kinematics and EMG of the right biceps femoris long head (BFlh) and semitendinosus (ST) muscles were recorded in 13 male sprinters during overground sprinting at maximum effort. The hamstring musculotendon lengths during sprinting were computed using a three-dimensional musculoskeletal model. The time of the peak musculotendon length, in terms of the percentage of the running gait cycle, was measured and compared with that of the peak EMG activity. The maximum length of the hamstring muscles was noted during the late swing phase of sprinting. The peak musculotendon length was synchronous with the peak EMG activation in the BFlh muscle, while the time of peak musculotendon length in the ST muscle occurred significantly later than the peak level of EMG activation (p < 0.05). These results suggest that the BFlh muscle is exposed to an instantaneous high tensile force during the late swing phase of sprinting, indicating a higher risk for muscle strain injury.

Effects of forward trunk lean on hamstring muscle kinematics during sprinting

Abstract 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.

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

ABSTRACT 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.

Gender differences in trunk acceleration and related posture during shuttle run cutting

Abstract Measurements using an accelerometer reflect the impact applied to the trunk. Measurement of trunk acceleration has the possibility of reflecting the typical characteristics of trunk motion during cutting. However, analysis of trunk acceleration data during cutting manoeuvres has not been previously conducted. This study aimed to analyse trunk acceleration during cutting manoeuvres to examine any gender differences or a relationship with posture. All participants (eight male and eight female college soccer athletes) performed a shuttle run cutting task, and trunk accelerations (medio-lateral, vertical, and antero-posterior) were calculated. The peak acceleration (G) and total magnitude during the 200 ms after foot contact were measured, and the forward trunk inclination and femoral angle were calculated from the video images taken using a sagittal plane camera. Peak vertical acceleration (mean, s) was significantly greater among female athletes than among male athletes (−2.18, s = 0.84 G; −1.15, s = 0.45 G, respectively; p < 0.01). Medio-lateral and antero-posterior peak acceleration and the total magnitude in all directions were not significantly different between genders. Moderate negative correlations were found between vertical peak acceleration and trunk forward inclination and femoral inclination (r = −0.57, p < 0.05; r = −0.69, p < 0.01, respectively). The difference in vertical acceleration between genders has the possibility to reflect a stiff cutting movement among female athletes. The acceleration of the upper trunk may be an index for evaluating cutting movements.

Change in muscle thickness under contracting conditions following return to sports after a hamstring muscle strain injury—A pilot study

The purpose of this study was to measure the change in hamstring muscle thickness between contracting and relaxing conditions following a return to sports after a hamstring muscle strain and thereby evaluate muscle function. Six male track and field sprinters participated in this study. All had experienced a prior hamstring strain injury that required a minimum of 2 weeks away from sport participation. Transverse plane scans were performed at the following four points on the affected and unaffected sides under contracting and relaxing conditions: proximal biceps femoris long head, proximal semitendinosus, middle biceps femoris long head, and middle semitendinosus. The results demonstrated an increase in the thickness of the middle biceps femoris long head and middle semitendinosus regions on the unaffected side with contraction, whereas the affected side did not show a significant increase. The proximal semitendinosus muscle thickness was increased with contraction on both the unaffected and the affected sides. By contrast, the proximal biceps femoris muscle thickness did not show a significant increase on both sides. The results of this study show that evaluation of muscle thickness during contraction may be useful for assessing the change in muscle function after a hamstring muscle strain injury.

NEUROMUSCULAR RESPONSES OF THE HAMSTRING MUSCLES DURING UNANTICIPATED TRUNK PERTURBATIONS

Background Anterior cruciate ligament and hamstring strain injuries occur during unanticipated cutting and stopping movements. Previous prospective studies showed that athletes with decreased trunk neuromuscular control are at increased risk of knee injury. Therefore, deficits in trunk neuromuscular control during unanticipated movements may result in injury. However, the modulations of the hamstring muscles to the unanticipated trunk perturbation are unclear. Objective To examine the neuromuscular responses of the hamstring muscles during unanticipated trunk perturbations. Design Descriptive laboratory study. Setting Male college athletes. Participants Eight male sprinters (age, 20.3±1.4 years). Intervention In the kneeling position, the participants wore a chest harness attached to a cable that was pulled backward as a resisting force at a constant level corresponding to 13% to 15% of each weight. The participants were instructed to resist the force isometrically. The force was released with cue (CUE) and without cue (NoCUE). Trunk acceleration and surface electromyography (EMG) signals of the erector spinae, gluteus maximus, biceps femoris, and semitendinosus muscles were measured. Main Outcome Measurements (1) Maximum trunk acceleration; (2) EMG activation in the 50-ms window before the perturbation; (3) onset time of the muscle response; and (4) phasic muscle activities after the perturbations. Results The maximum trunk acceleration was significantly greater during the NoCUE condition than during the CUE condition (p<0.01). No significant differences were observed in either of the EMG activations before the perturbation. The activation onsets of the hamstring muscles were significantly delayed (p<0.05) and the activation responses of these muscles from 100 ms after the perturbation were significantly larger during the NoCUE than during the CUE condition (p<0.05). Conclusions The results indicate that the anticipation of perturbation decreased the hamstring muscle latencies and responses to control the trunk movement, suggesting that the central nervous system modulated the readiness of the trunk based on anticipatory information.

POTENTIAL RISK FACTORS FOR HAMSTRING MUSCLE STRAIN INJURY DURING THE LATE SWING PHASE OF SPRINTING

Background The hamstring muscles are susceptible to strain injury during sprinting, and the biceps femoris long head (BFlh) is reportedly the most frequently injured muscle. Therefore, elucidation of the risk factors is of particular concern for injury prevention. Objective To clarify the potential risk factors for the incidence of muscle strain injury in each hamstring muscle by comparing the time of occurrence of peak musculotendon length and electromyography (EMG) activation during the late swing phase of sprinting. Design Descriptive laboratory study. Setting Male college track and field athletes. Participants 13 male sprinters (age 20.2±0.6 years). Intervention Full-body kinematics and EMG of the BFlh and semitendinosus (ST) were recorded during overground sprinting at maximum effort. The hamstring musculotendon lengths were computed by using a three-dimensional musculoskeletal model. Main outcome measurements The time at the peak musculotendon length, in terms of percentage of the running gait cycle, was calculated and compared with that of the peak EMG activity. Results The peak length of the BFlh and ST was observed during the late swing phase, at 86.7% [2.5%] and 81.1% [2.5%] gait cycle, respectively (mean [SD]). A significant difference was observed in the time of the peak musculotendon length (P<.001). Peak EMG activation time of the BFlh occurred significantly later (86.0% [7.9%] gait cycle, P<.01) than that of the ST (76.2% [7.8%] gait cycle). The peak musculotendon length was synchronous with the peak EMG activation in the BFlh, while a statistically significant difference was observed between these values in the ST (P<.05). Conclusions The results indicate that the BFlh is exposed to instantaneous high tensile force during the late swing phase of sprinting, suggesting a higher potential risk for strain injury among the hamstring muscles.