Affiliations: [a] Human Performance Laboratory, UNESP, Rio Claro,
São Paulo, Brazil
Note: [] Corresponding author: B.S. Denadai, Human Performance
Laboratory, UNESP. Av. 24 A, 1515, Bela Vista, Rio Claro, SP, CEP, 13506-900,
Brazil. Tel.: +55 19 35264325; Fax: +55 19 35264321; E-mail: bdenadai@rc.unesp.br
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/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.
