Rapid hamstrings/quadriceps strength capacity in professional soccer players with different conventional isokinetic muscle strength ratios

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Muscle strength imbalance can be an important factor in hamstrings muscle strain. A hamstrings/quadriceps (H/Q) strength ratio based on concentric peak torque values (H-con:Q(con)) has traditionally been used to describe the potential for knee-joint destabilization. Because certain standard actions in soccer are explosive, the analysis of the H/Q strength ratio based on the rate of torque development (H-rtd:Q(rtd)) might also be useful in the evaluation of joint stability. The objective of this study was to compare the H-rtd:Q(rtd) between professional soccer players with heterogeneous values of H-con:Q(con). Thirty-nine professional soccer players took part in the following procedures on different days: 1) Familiarization session with the isokinetic dynamometer, and 2) Two maximal isometric actions and five maximal concentric actions at 60 degrees.s(-1) for hamstrings (H) and quadriceps (Q). Participants were ranked according to their H-con:Q(con) ratio. The median third was excluded to form a high torque group (HTG), and a low torque group (LTG). Peak isometric (H) and concentric (H and Q) torques and rate of torque development (H) were significantly greater in the HTG group. Similarly, H-con:Q(con) (0.68 +/- 0.02 vs. 0.52 +/- 0.03) and H-rtd:Q(rtd) (0.54 +/- 0.12 vs. 0.43 +/- 0.16) were significantly greater in the HTG group than in the LTG group. There was no significant correlation between H-con:Q(con) and H-rtd:Q(rtd). It can be concluded that H-con:Q(con) and H-rtd:Q(rtd) are determined, but not fully defined, by shared putative physiological mechanisms. Thus, the physiologic and clinical significance of H-con:Q(con) and H-rtd:Q(rtd) to an athlete's individual evaluation might be different.