The effect of hamstring flexibility on peak hamstring muscle strain in sprinting

Background:The effect of hamstring flexibility on the peak hamstring muscle strains in sprinting,until now,remained unknown,which limited our understanding of risk factors of hamstring muscle strain injury(hamstring injury).As a continuation of our previous study,this study was aimed to examine the relationship between hamstring flexibility and peak hamstring muscle strains in sprinting.Methods:Ten male and 10 female college students participated in this study.Hamstring flexibility,isokinetic strength data,three-dimensional(3D)kinematic data in a hamstring isokinetic test,and kinematic data in a sprinting test were collected for each participant.The optimal hamstring muscle lengths and peak hamstring muscle strains in sprinting were determined for each participant.Results:The muscle strain of each of the 3 biarticulated hamstring muscles reached a peak during the late swing phase.Peak hamstring muscle strains were negatively correlated to hamstring flexibility(0.1179 ≤ R2≤ 0.4519,p = 0.001) but not to hip and knee joint positions at the time of peak hamstring muscle strains.Peak hamstring muscle strains were not different for different genders.Peak muscle strains of biceps long head(0.071 ± 0.059) and semitendinosus(0.070 ± 0.055) were significantly greater than that of semimembranosus(0.064 ± 0.054).Conclusion:A potential for hamstring injury exists during the late swing phase of sprinting.Peak hamstring muscle strains in sprinting are negatively correlated to hamstring flexibility across individuals.The magnitude of peak muscle strains is different among hamstring muscles in sprinting,which may explain the different injury rate among hamstring muscles.

Research in prevention and rehabilitation of hamstring muscle strain injury

Hamstring muscle strain injury is the most common and prevalent injury in sports involving high-speed running,such as American football,Australian football,English rugby,soccer,track and field,and cricket.1Hamstring muscle strain injury also has a high recurrence rate of up to 48%.2The average practice and game time loss due to hamstring injury is between17 and 60 days,contingent on the grade of injury.2Severe hamstring muscle strain injuries,and associated recurrent inju-

The Effect of Hamstring Stretching on Muscle Hardness and Isokinetic Muscle Performance

The purpose of this study was to clarify the effects and the time course of moderate hamstring stretching on the hardness and strength of the knee flexor muscles. Thirteen young adults performed static stretching of their hamstrings （2 minx 3 repetitions）. Before and after the static stretching, muscle hardness and concentric isokinetic torque of the knee flexors （180~/s） was determined. The hardness of the long head of the BF （biceps femoris） muscle was measured by using shear wave ultrasound elastography images. To follow the time course of the stretching effects, we determined the above parameters before, immediately after, and every 10 min for torque and every 5 min for muscle hardness until 30 min after stretching. Muscle hardness of the BF significantly decreased when compared with before the stretching （P 〈 0.001）, and remained significantly reduced until 25 min. However, the knee flexion torque did not show any change at any timing. As seen in this experiment, moderate stretching decreased the muscle hardness of the BF without a decline in the knee flexion torque. Thus, these findings suggest that moderate stretching is useful as a warm-up maneuver.