Repeated sprints alter mechanical work done by hip and knee, but not ankle, sagittal moments

To quantify the changes in work done by lower limb joint moments during maximal speed running following a sports-specific repeated running protocol.

Observational with repeated-measures.

Recreational athletes (n = 18 (9 females), aged = 26.2 ± 6.2 years) performed 12 maximal 30-m sprints on a non-motorised treadmill. Three-dimensional kinematics and ground reaction forces were subsequently recorded during a 10-m maximal overground sprint before and immediately after the repeated running protocol, from which we calculated work done by sagittal plane hip, knee, and ankle moments. Relative work (J/kg) was reported as a percentage of positive and negative work done by the sum of joint moments.

Following the repeated running protocol, maximal sprint speed decreased by 19% and was accompanied by reductions in total positive (-1.47 J/kg) and negative (-0.92 J/kg) work, in addition to work done by hip (-0.43 to -0.82 J/kg) and knee (-0.28 J/kg) moments during swing. Compared to before the repeated running protocol, less relative work was done by hip (-9%) and knee (-3%) extension moments during swing. Reductions in work done by hip and knee joint moments during swing were significantly correlated with reductions in maximum running speed (r = 0.61-0.89, p < 0.05).

A sports-specific repeated running protocol resulted in reductions in mechanical work done by sagittal plane hip and knee joint moments during maximal overground sprinting. Interventions focused on maintaining positive work done by the hip flexors/extensors and negative work done by knee flexors/extensors during the swing phase of running may help prevent reductions in speed following repeated sprinting.