The Influence Of Hamstring Muscle-tendon Stiffness On Isolated And Dynamic Velocity Based Parameters

Abstract

Previous research has demonstrated sex differences in active hamstring muscle-tendon stiffness as well as associations between stiffness and landing biomechanics and architectural tissue properties. Little is known whether active stiffness relates to other measures of muscle function (i.e., maximum voluntary isometric contraction [MVIC], isotonic dynamometry) and performance (i.e., sprinting). PURPOSE: To conduct a pilot study examining the relationship between active hamstring muscle-tendon stiffness and isometric torque production, isotonic velocity development, and sprint velocity. A secondary research interest was to examine the relationship between the isotonic velocity parameters and sprint performance. METHODS: Nine recreationally active and healthy subjects (7 males, 2 females) (24 ± 3 years) completed an MVIC for the hamstrings (30° knee flexion) followed by three 40m sprint trials using an infrared timing gate system (Brower, Draper, UT). At least 48 hours later, subjects completed a measure of hamstring muscle-tendon stiffness (damped oscillatory technique) and an isotonic knee flexion test on a fixed dynamometer (Biodex, Shirley, NY). The isotonic test began at 90° of knee flexion and was eccentric/concentric through a 90° arc of motion with subjects lying prone. Eccentric velocity was set at 180°/s and concentric torque was set at 25% of MVIC. Bivariate correlations were conducted between stiffness, MVIC (normalized to body mass), sprint times, time to peak velocity, rate of velocity development (RVD, 0-100ms), and rebound time (-50°/s to +50°/s). RESULTS: Stiffness (24.3 ± 11.7 Nm/kg) was only significantly related (r= .681, P= .043) to MVIC (1.48 ± 0.23 Nm/kg). Stiffness was not significantly related to rebound time (0.076 ± 0.026s) (r= -.354, P= .350), time to peak velocity (0.214 ± 0.034s) (r= -.285, P= .457), RVD0-100 (1314.64 ± 222.30°/s2) (r= -.336, P= .377), or sprint velocities (5.90 ± 0.56 m/s) (r= .248, P= .521). Rebound time (r= -.535, P= .138) and RVD0-100 (r= -.436, P= .241) were not significantly related to sprint times. CONCLUSIONS: Although only the association between stiffness and normalized MVIC reached statistical significance, the magnitude of the other observed relationships provides impetus for further study with a larger sample size.