Reduced strength after passive stretch of the human plantarflexors

The purpose of this study was to assess strength performance after an acute bout of maximally tolerable passive stretch (PSmax) in human subjects. Ten young adults (6 men and 4 women) underwent 30 min of cyclical PSmax (13 st retches of 135 s each over 33 min) and a similar control period (Con) of no stretch of the ankle plantarflexors. Measures of isometric strength (maxim al voluntary contraction), with twitch interpolation and electromyography, and twitch characteristics were assessed before (Pre), immediately after (P ost), and at 5, 15, 30, 45, and 60 min after PSmax or Con. Compared with Pr e, maximal voluntary contraction was decreased at Post (28%) and at 5 (21%) , 15 (13%), 30 (12%), 45 (10%), and 60 (9%) min after PSmax (P < 0.05). Mot or unit activation and electromyogram were significantly depressed after PS max but had recovered by 15 min. An additional testing trial confirmed that the torque-joint angle relation may have been temporarily altered, but at Post only. These data indicate that prolonged stretching of a single muscle decreases voluntary strength for up to 1 h after the stretch as a result o f impaired activation and contractile force in the early phase of deficit a nd by impaired contractile force throughout the entire period of deficit.