In epimuscularly connected muscle previous activity at high length yields sizable history effects causing decreased muscle force at low lengths

Abstract

History effects are the changes in isometric forces of muscles previously activated at high length. The aim of our study was to investigate determinants of history effects in the context of epimuscular myofascial force transmission. Isometric forces of maximally active extensor digitorum longus (EDL) muscle, as well as tibialis anterior and extensor hallicus longus muscle complex (TA+EHL) of the rat were measured simultaneously. (i) length-force (l-f) data were collected and (ii) control measurements were performed at EDL optimum (higher) length and ii) at reference (lower) length. Between consecutive contractions muscles were allowed to recover for 2 min. History effects were quantified as Fl-f-Fcontrol for the indicated lengths. 4 conditions were studied: (1) in the intact condition, during extensor digitorum longus (EDL) lengthening, at low length of EDL, history effects were 45.49%. However, no significant effects were shown for the forces at high length of EDL and restrained TA+EHL. (2) Second control measurements taken 15 minutes after first ones showed that extra time increased the history effects (i.e. EDL proximal force decrease increased from 41.53% to 55.69%). (3) After simultaneous lengthening of EDL and TA+EHL history effects decreased by 42.12% (4) History effects decreased to %34.92 after blunt dissection and 29.56% after fasciotomy. Our study showed that history effect is a fundamental phenomenon determined by intrinsic muscle properties and epimuscular connections may change this effect.