Factors Affecting Force Loss With Prolonged Stretching

TLDR

The study aimed to identify factors contributing to force loss after prolonged static passive stretching. Twenty minutes of static passive quadriceps stretching was applied to 12 participants, with MVC, iEMG, twitch/tetanic force, and ITT measured before and 5–10 min after; a control group of six underwent no stretch. After stretching, MVC decreased by 12 %, muscle inactivation (ITT) rose 2.8 % and iEMG increased 20.2 %, twitch force fell 11.7 % while tetanic force remained unchanged, indicating that force loss is mainly due to muscle inactivation rather than changes in elasticity. Keywords: antagonist, electromyography, maximum voluntary contraction, muscle activation, twitch, tetanus.

Abstract

The purpose of this study was to investigate factors underlying the force loss occurring after prolonged, static, passive stretching. Subjects were tested before and 5-10 min following 20 min of static, passive stretching of the quadriceps (N = 12) or a similar period of no stretch (control, N = 6). Measurements included isometric maximal voluntary contraction (MVC) force, surface integrated electromyographic (iEMG) activity of the quadriceps and hamstrings, evoked contractile properties (twitch and tetanic force), and quadriceps inactivation as measured by the interpolated twitch technique (ITT). Following stretching, there was a significant 12% decrement in MVC with no significant changes in the control group. Muscle inactivation as measured by the ITT and iEMG increased by 2.8% and 20.2%, respectively. While twitch forces significantly decreased 11.7%, there was no change in tetanic force post-stretch. Although possible increases in muscle compliance affected twitch force, a lack of tetanic force change would suggest that post-stretch force decrements are more affected by muscle inactivation than changes in muscle elasticity. Key Words: antagonist, electromyography, maximum voluntary contraction, muscle activation, twitch, tetanus