Correlation between stiffness and electromechanical delay components during muscle contraction and relaxation before and after static stretching. (April 2017) - Longo, Stefano
Abstract: The study was aimed at assessing possible correlations of the electromechanical delay components during muscle contraction (DelayTOT ) and relaxation (R-DelayTOT ), with muscle-tendon unit (MTU), muscle, and tendon stiffness before and after static stretching (SS). Plantarflexor muscles' maximum voluntary torque (Tmax ) was measured in 18 male participants (age 24 ± 3 yrs; body mass 76.4 ± 8.9 kg; stature 1.78 ± 0.09 m; mean ± SD). During Tmax, surface electromyogram (EMG), mechanomyogram, and force signals were detected. DelayTOT and R-DelayTOT with their electrochemical and mechanical components were calculated. Passive torque and myotendinous junction displacement were assessed at 0°, 10° and 20° of dorsiflexion to determine MTU, muscle and tendon stiffness. The same protocol was repeated after SS. DelayTOT, R-DelayTOT and their mainly mechanical components correlated with MTU, muscle and tendon stiffness, both before ( R 2 from 0.562 to 0.894; p < 0.001) and after SS ( R 2 from 0.726 to 0.955; p < 0.001). SS decreased Tmax (−14%; p < 0.001) and lengthened almost all the DelayTOT and R-DelayTOT components (from +5.9% to +30.5%; p < 0.05). Correlations were found only between stiffness and the mechanical components of DelayTOT and R-DelayTOT . Correlations persisted after SS but delays increased to a higher extent than stiffness, indicating a complexity of the relationship between stiffness and delays that will be discussed in the manuscript.