Acute Effects of a Fatiguing Protocol on Peak Force and Rate of Force Development of the Hamstring Muscles in Soccer Players

Hamstring strain injuries (HSI) represent a significant burden in soccer. High-speed running is one of the most common HSI mechanism, in particular during match congested periods. Peak force and rate of force development (RFD) of the hamstring muscles tested at long muscle length have shown reductions following fatiguing tasks. However, no study has used a meticulous fatiguing protocol nor reliability scores have been provided. Hamstring peak force, RFD₅₀₋₁₀₀ and RFD_{100 −150} were assessed at long muscle length in 19 soccer players (26.0 ± 4.1 years) before and after the repeated sprint ability (RSA) test. We aimed to calculate reliability scores for both limbs before and after the fatiguing task, and to compare peak force, RFD₅₀₋₁₀₀ and RFD_100−150 following the RSA test to baseline values. Peak force displayed “excellent” reliability scores before and after the RSA test, whereas RFD ICC showed “good” values in both time points, but CV scores were not acceptable (i.e. > 10%). Significant moderate to large decreases were found in peak force (g = − 1.11 to − 0.90), RFD₅₀₋₁₀₀ (g = − 1.37 to − 1.11) and RFD_100−150 (g = − 0.84 to − 0.69) in both dominant and non-dominant limbs. Maximal isometric peak force, RFD₅₀₋₁₀₀ and RFD_100−150 of the hamstrings tested at long muscle length reduced following the RSA test. However, only peak force displayed “excellent” reliability scores, whereas RFD measures could not be considered acceptable owing to their lower reliability scores. Thus, practitioners can be confident about peak force changes, whilst caution should be used when examining such changes in RFD.