Abstract
The hamstring muscles are the most injured muscles in athletes practicing sprints. However, they seem greatly contributing to the production of horizontal force, a key element in the sprint acceleration performance. The aim of our study was to experimentally analyse the link between the production of horizontal force and strength of the hamstrings at maximum sprints on a treadmill and in fatigue conditions. Fourteen male subjects accustomed to sprint participated in the experiment consisting in 12 6-seconds sprints separated by 44 seconds of recovery on an instrumented treadmill sprint for measuring the horizontal force, coupled with the simultaneous recording of the EMG activity of the vastus lateralis, rectus biceps femoris and gluteus muscles. Before and after the 12 sprints, the maximum isokinetic strength of the flexors and extensors of the hip and knee was measured on isokinetic dynamometer type CONTREX with 3 maximum repetitions at 120°/s in concentric and eccentric. A comparison before and after analysis and correlation between the parameters was carried out. At the maximum sprint, the multiple linear regression analysis showed a significant relationship ( P = 0.02) between the horizontal force and the combination of EMG activity of the biceps femoris in late swing phase of the stride and the eccentric isokinetic strength of the knee flexors. After the 12 sprints, there was a significant decrease ( P < 0.05) in the sprint performance, horizontal force, isokinetic strength and muscle activity. And there was a significant correlation between the horizontal force and eccentric strength of the knee extensors, and concentric strength of hip extensors. For a high-performance acceleration, it would seem necessary to be able both to strongly activate the hamstrings just before ground contact and have a great capacity eccentric strength of the hamstrings. In fatigue conditions, horizontal force reduction would seem not only related to the strength of decreased hamstring, but with d knee extensors eccentric strength decrease.
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