The Effect Of Flexibility And Strength On Biomechanical Property Of Hamstring During Sprinting

Purpose: Hamstring muscle strain injury(hamstring injury)is one of the most common injuries in sports.Whether the hamstring flexibility and strength are risk factors for hamstring injury during sprinting are indeterminate.Previous studies demonstrated that the direct cause of muscle strain injury is muscle strain during muscle eccentric contraction.The purpose of this study was to examine the relationships among hamstring flexibility and strength,hamstring muscle optimal lengths and peak hamstring muscle strains in sprinting.Methods: Twenty male and twenty female college students with sprint training experience participated in this study.Hamstring flexibility,isokinetic strength data,three-dimensional kinematic data in a hamstring isokinetic test,and kinematic data in a sprinting test were collected for each participant.The joint angle,moment,and power of lower extremity,the optimal hamstring muscle lengths and peak hamstring muscle strains in sprinting were determined for each participant.Results: Hamstring muscle optimal lengths were longer than corresponding hamstring muscle lengths in standing,and the correlation coefficients were low(0.1179 ? R2 ? 0.2513).Hamstring muscle optimal lengths were significantly correlated to hamstring flexibility score(0.3347 ? partial R2 ? 0.4143)and gender(0.0781 ? partial R2 ? 0.1318),but not to hamstring maximum contraction strength.With the same flexibility score,females tend to have shorter hamstring optimal muscle lengths compared to males.Hamstring flexibility score and hamstring maximum contraction strength were not correlated.The muscle strain of each of the three biarticulate hamstring muscles reached a peak during the late swing phase.Peak hamstring muscle strains were negatively correlated to hamstring flexibility(0.3610 ? R2 ? 0.4332)but not to hamstring maximum contraction strength,peak hamstring lengths,and hip-knee joint 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 and semitendinosus were significantly greater than that of semimembranosus.Conclusion: Hamstring flexibility are positively correlated to hamstring optimal muscle lengths and negatively correlated to peak hamstring muscle strains in sprinting.But hamstring maximum contraction strength is not correlated to hamstring optimal muscle lengths and peak hamstring muscle strains.Hamstring flexibility may be a risk factor for hamstring injury.The potential for hamstring muscle strain injury may exist during the late swing phase of sprinting.Hamstring muscle lengths in standing should not be used as an approximation of their optimal lengths.With the same flexibility,females tend to have shorter hamstring optimal muscle lengths compared to males,but peak hamstring muscle strains were not different for different genders.Hamstring flexibility and maximum contraction strength are not correlated across individuals.The magnitude of peak muscle strains are different among hamstring muscles in sprinting,which may explain the different injury rate among hamstring muscles.