Relationships between isokinetic knee strength, single-sprint performance, and repeated-sprint ability in football players

Previous research has demonstrated that muscular strength of the knee extensors is related to the speed an athlete can produce during a single-sprint performance. Football players, as well as many other athletes on the field and the court, execute multiple sprints during the course of a match. The purpose of this study was to examine the relationships between leg strength, single-sprint speed, and repeated-sprint ability. Thirty-eight football players from 3 codes (soccer, rugby league, rugby union) completed a 12- x 20- m repeated-sprint protocol and were evaluated for peak isokinetic knee extension and flexion torque at 608[middle dot]s-1, 1508[middle dot]s-1, and 2408[middle dot]s-1. Although single-sprint performance correlated with peak extensor and flexor torque at all velocities, the strongest correlation was observed between relative knee extensor torque at 2408[middle dot]s-1 and the initial acceleration phase (0-10 m) of the single-sprint performance (r 520.714, p < 0.01). However, the data suggest that factors other than strength contribute to repeated-sprint ability. This finding provides new evidence in elucidating the relationship between strength and repeated-sprint performance.