The relationship between sprint speed and hip flexion/extension strength in collegiate athletes

The evaluation of strength and the development of methods to improve strength in the lower extremity are integral areas of interest in biomechanics and athletic training. Contemporary research has established that (1) the hip extensors and the hip flexors are the strongest muscle groups within the lower extremity, and (2) the extensors are the primary movers by acceleration of the body's center of gravity. Thus, the purpose of this study was to determine the relationship between sprint speed and hip flexor/extensor strength measured from a functional position. Forty-one intercollegiate athletes (mean age-19.4 yr, mean weight = 194.5 lbs) participated in this study. Sprint speed (SS) was determined from the mean of three 40-yard sprints on artificial turf. Muscular assessment was performed using a Cybex II isokinetic testing device. Test speeds of 60 deg/sec and 240 deg/sec were selected for assessment of peak torque (PT), peak torque/body weight (PT/BW), torque acceleration energy (TAE), average power, flexion/extension ratios, and endurance ratios. Unlike previous research, this strength assessment was performed from a functional standing position (right leg testing). A reliability study established consistency of strength measures on different occasions. Absolute intraclass correlation coefficients (ICC) of 0.91, 0.96, 0.93, and 0.82 were established for flexion at 60 deg/sec, extension at 60 deg/sec, flexion at 240 deg/sec, and extension at 240 deg/sec, respectively. Results of regression analysis showed significant (p ' 0.01) correlations between SS and flexion PT/BW at 60 deg/sec (r=−0.57), extension PT/BW at 60 deg/sec (r=−0.56), flexion PT/BW at 240 deg/sec (r=−0.42), and extension PT/BW at 240 deg/sec (r=−0.41). This study suggests that when tested functionally, there appears to be a strong relationship between hip flexion and extension strength relative to body weight and SS. Additionally, it suggests that a cause/effect relationship could exist between enhanced hip flexion/extension strength and sprint speed.