Influence of hip-flexion angle on hamstrings isokinetic activity in sprinters.
BACKGROUND
Hamstrings strains are common and debilitating injuries in many sports. Most hamstrings exercises are performed at an inadequately low hip-flexion angle because this angle surpasses 70° at the end of the sprinting leg's swing phase, when most injuries occur.


OBJECTIVE
To evaluate the influence of various hip-flexion angles on peak torques of knee flexors in isometric, concentric, and eccentric contractions and on the hamstrings-to-quadriceps ratio.


METHODS
Descriptive laboratory study.


METHODS
Research laboratory.


METHODS
Ten national-level sprinters (5 men, 5 women; age = 21.2 ± 3.6 years, height = 175 ± 6 cm, mass = 63.8 ± 9.9 kg).


METHODS
For each hip position (0°, 30°, 60°, and 90° of flexion), participants used the right leg to perform (1) 5 seconds of maximal isometric hamstrings contraction at 45° of knee flexion, (2) 5 maximal concentric knee flexion-extensions at 60° per second, (3) 5 maximal eccentric knee flexion-extensions at 60° per second, and (4) 5 maximal eccentric knee flexionextensions at 150° per second.


METHODS
Hamstrings and quadriceps peak torque, hamstrings-to-quadriceps ratio, lateral and medial hamstrings root mean square.


RESULTS
We found no difference in quadriceps peak torque for any condition across all hip-flexion angles, whereas hamstrings peak torque was lower at 0° of hip flexion than at any other angle (P < .001) and greater at 90° of hip flexion than at 30° and 60° (P < .05), especially in eccentric conditions. As hip flexion increased, the hamstrings-to-quadriceps ratio increased. No difference in lateral or medial hamstrings root mean square was found for any condition across all hip-flexion angles (P > .05).


CONCLUSIONS
Hip-flexion angle influenced hamstrings peak torque in all muscular contraction types; as hip flexion increased, hamstrings peak torque increased. Researchers should investigate further whether an eccentric resistance training program at sprint-specific hip-flexion angles (70° to 80°) could help prevent hamstrings injuries in sprinters. Moreover, hamstrings-to-quadriceps ratio assessment should be standardized at 80° of hip flexion.
Department of Physiotherapy, School of Health Sciences, University of Applied Sciences Western Switzerland, Lausanne, Switzerland. kenny.guex@hesav.ch
Kenny
K
Guex
Boris
B
Gojanovic
Grégoire P
GP
Millet
D001696:Biomechanical Phenomena; D015444:Exercise; D005260:Female; D025981:Hip Injuries / Q000517:prevention & control; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction; D007719:Knee Joint; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000293:injuries / Q000502:physiology; D016059:Range of Motion, Articular; D012420:Running / Q000502:physiology*; D013180:Sprains and Strains / Q000517:prevention & control*; D019415:Torque; D055815:Young Adult