In this study, we examined hamstring muscle activation at different running speeds to help better understand the functional characteristics of each hamstring muscle. Eight healthy male track and field athletes (20.1 +/- 1.1 years) performed treadmill running at 50%, 75%, 85%, and 95% of their maximum velocity. Lower extremity kinematics of the hip and knee joint were calculated. The surface electromyographic activities of the biceps femoris and semitendinosus muscles were also recorded. Increasing the running speed from 85% to 95% significantly increased the activation of the hamstring muscles during the late swing phase, while lower extremity kinematics did not change significantly. During the middle swing phase, the activity of the semitendinosus muscle was significantly greater than that of the biceps femoris muscle at 75%, 85%, and 95% of running speed. Statistically significant differences in peak activation time were observed between the biceps femoris and semitendinosus during 95%max running (P < 0.05 for stance phase, P < 0.01 for late swing phase). Significant differences in the activation patterns between the biceps femoris and semitendinosus muscles were observed as running speed was increased, indicating that complex neuromuscular coordination patterns occurred during the running cycle at near maximum sprinting speeds.

This study was designed to determine the regional differences of magnetic resonance (MR) measurements in the hamstrings [biceps femoris muscle long head (BFl) and short head (BFs), semimembranosus muscle (SM), and semitendinosus muscle (ST)] following eccentric knee-flexion exercise. Twelve male volunteers performed eccentric knee-flexion exercise. Maximum isometric torque, plasma creatine kinase (CK) activity, muscle soreness, and MR images of the hamstrings were measured before and immediately following exercise, and on the first, second, third and seventh days following the exercise. Cross-sectional areas (CSAs) and transverse relaxation times (T2s) of the hamstrings were measured from the T2-weightened MR imaging sequences of 30% (proximal), 50% (middle), and 70% (distal) areas of the thigh length. The CSA of the ST at proximal and middle regions had significantly increased on the third day, but no significant changes were found for the BFl or SM. Immediately following exercise, T2 values had increased significantly in the BFs, BFl, and ST. On the third day, T2 values of only ST increased significantly at proximal, middle and distal regions. Significant differences of T2 values between proximal and distal regions in the ST were found for the second, third and seventh days following the exercise. These results suggest that because of the anatomical characteristics of the muscles, the degrees of response following the exercise differed among the muscles and the regions of ST muscle.

Excessive competitive swimming activities might exaggerate lumbar intervertebral disk degeneration, especially in the L5-S1 intervertebral segment.

The purpose of this study was to clarify the activation patterns among knee flexor muscles during knee flexion exercises by electromyography (EMG) and muscle functional magnetic resonance imaging (mfMRI). Seven male volunteers performed knee flexion exercises with each unilateral limb at 120% of 1 repetition of maximum (1RM) and 50% of 1RM. EMG activity was recorded for the biceps femoris long head, semitendinosus (ST), semimembranosus (SM), and gracilis (G) muscles; mfMRI T2 values in the same muscles were measured at rest and immediately after exercise. The study found that EMG of the ST and G was significantly higher than that of the SM during the exercises at 120% 1RM. T2 value changes in the ST and G were significantly higher than in the biceps femoris long head (BFlh) and SM in both exercises [corrected].It was concluded that the activation patterns among knee flexor muscles during knee flexion were nonuniform for the respective muscles.

To investigate the effects of cooling on local temperature and circulation in the skin and skeletal muscle at different cooling temperatures. Ten male subjects (mean age 24.9 years) participated in this study. Intramuscular temperatures were measured by inserting two 22-gauge temperature probes (needle length; 8 and 18 mm) into the ankle dorsiflexors, while skin temperature was measured using a thermocouple attached to the leg skin anteriorly. Near-infrared spectroscopy was also used to evaluate the concentration changes in oxygenated, deoxygenated, and total hemoglobin/myoglobin in local skin and skeletal muscle. These measurements were simultaneously performed during the 10-min noncooling, 30-min cooling (cooling pad temperature; 0, 10, or 20 degrees C), and 60-min recovery periods. Under all cooling conditions, skin and intramuscular temperatures decreased during cooling (P < 0.01) and began to increase after the cooling pad was removed. However, these values did not return to baseline values during the recovery period (P < 0.01). Moreover, tissue temperatures tended to show lower values during cooling at lower cooling temperatures. All hemoglobin/myoglobin concentrations also showed a concomitant significant decrease during cooling under three cooling conditions (P < 0.01); the oxygenated and total hemoglobin/myoglobin concentrations did not return to the exact values before cooling during the recovery period. This study suggested that the rate of decrease in tissue temperature depends on the cooling temperature and the effects of cooling on tissue temperatures and circulation tend to be maintained during 60 min post-cooling period despite the cooling temperature.