STUDY DESIGN: Prospective cohort study. OBJECTIVES: In this prospective cohort study of elite sprinters, muscle strength of the hip extensors, as well as of the knee extensors and flexors, was measured to determine a possible relationship between strength deficits and subsequent hamstring injury within 12 months of testing. The method used for testing muscle strength simulated the specific muscle action during late swing and early contact phases when sprinting. BACKGROUND: There have been no prospective studies in elite sprinters that examine the concentric and eccentric isokinetic strength of the hip extensors and the quadriceps and hamstring muscles in a manner that reflects their actions in late swing or early contact phases of sprinting. Consequently, the causal relationship between hip and thigh muscle strength and hamstring injury in elite sprinters may not be fully understood. METHODS AND MEASURES: Isokinetic testing was performed on 30 male elite sprinters to assess hip extensors, quadriceps, and hamstring muscle strength. The occurrence of hamstring injury among the subjects was determined during the year following the muscle strength measurements. The strength of the hip extensors, quadriceps, and hamstring muscles, as well as the hamstrings-quadriceps and hip extensors- quadriceps ratios were compared. RESULTS: Hamstring injury occurred in 6 subjects during the 1-year period. Isokinetic testing at a speed of 60°/s revealed weakness of the injured limb with eccentric action of the hamstring muscles and during concentric action of the hip extensors. When performing a side-to-side comparison for the injured sprinters, the hamstring injury always occurred on the weaker side. Differences in the hamstrings-quadriceps and hip extensors-quadriceps strength ratios were also evident between uninjured and injured limbs, and this was attributable to deficits in hamstring strength. CONCLUSION: Hamstring injury in elite sprinters was associated with weakness during eccentric action of the hamstrings and weakness during concentric action of the hip extensors, but only when tested at the slower speed of 60°/s.

J Orthop Sports Phys Ther. 2008;38(8):457-464, published online 15 April 2008. doi:10.2519/jospt.2008.2575

KEY WORDS: isokinetics, quadriceps, running, sprinting