Moderate intensity and volume downhill run does not impair knee joint stability at early and late phases of quadriceps/hamstrings contraction

Abstract

BACKGROUND AND OBJECTIVE: Muscle strength imbalance can be an important factor in hamstrings muscle strain. The main purpose of this study was to investigate the effects of downhill running on hamstrings/quadriceps torque (H/Qtorque) and the electromechanical delay (H/QEMD) ratios. METHODS: Fifteen active male individuals performed two maximal voluntary isometric contractions of the knee extensors and knee flexors, from which the maximal muscle torque, EMD and H/Qtorque and H/QEMD ratios were extracted. Thereafter, the participants performed a 30-minute downhill run (−16%) at 70% VO2max. Dependent variables were assessed immediately before, immediately following and 48 hours after the effort. RESULTS: Maximal isometric torque decreased significantly immediately after the downhill run for both the extensors (pre: 271.8 ± 45.9 N·m; post: 235.5 ± 55.7 N·m) and flexors (pre: 112.2 ± 26.3 N·m; post: 97.7 ± 27.2 N·m). No significant difference was identified over time for the EMD of the vastus lateralis and biceps femoris muscles. The H/Qtorque and H/QEMD ratios were not influenced by the downhill run. CONCLUSION: We have demonstrated that moderate intensity and volume downhill run does not impair knee joint stability at early (H/QEMD) and late phases (H/Qtorque) of quadriceps/hamstrings contraction.