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

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/Q _{torque} ) and the electromechanical delay(H/Q _{EMD} ) 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/Q _{torque} and H/Q _{EMD} ratios were extracted. Thereafter, the participants performed a 30-minute downhill run (−16%) at 70% VO _{2} max. 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/Q _{torque} and H/Q _{EMD} 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/Q _{EMD} ) and late phases (H/Q _{torque} ) of quadriceps/hamstrings contraction.