The history dependence of force production in mammalian skeletal muscle following stretch-shortening and shortening-stretch cycles

The purpose of this study It as to determine the history dependence of forc e production during and following stretch-shortening and shortening-stretch cycles in mammalian skeletal muscle. Thirty-three different isometric, str etch, shortening, stretch-shortening and shortening-stretch experiments wer e preformed in cat soleus (n = 8) using previously established methods. Str etch-shortening and shortening-stretch cycles are not commutative with resp ect to the isometric forces following the length changes. Whereas force dep ression following shortening is virtually unaffected by previous stretching of the muscle. force enhancement following stretch depends in a dose-depen dent manner on the amount of muscle shortening preceding the stretch. The h istory dependence of isometric force following shortening-stretch cycles ca n conveniently be modelled using an elastic (compressive and tensile) eleme nt that engages at the length of muscle activation. Such an "elastic" mecha nism has been proposed by Edman and Tsuchiya (1996) (Edman, K.A.P., Tsuchiy a, T., 1996. Strain of passive elements during Force enhancement by stretch in frog muscle fibres. Journal of Physiology 490.1, 191-205) based on expe rimental observations, and has been implemented theoretically in a rheologi cal model of muscle (Forcinito et al., 1997) (Forcinito, hi., Epstein, M., Herzog, W., 1997. Theoretical considerations on myofibril stiffness. Biophy sics Journal 72, 1278-1286. The history dependence of isometric force follo wing stretch-shortening cycles appears independent of the stretch preceding the shortening, except perhaps, if stretching occurs at very high speeds ( i.e. 6-10 times fibre length per second). The results of this study are har d to reconcile with the two major mechanisms associated with history depend ence of force production: sarcomere length non-uniformity (Edman et al., 19 93) and stress-induced cross-bridge inhibition (Marechal and Plaghki, 1979) (Marechal, G., Plaghki, L., 1979. The deficit of the isometric tetanic ten sion redeveloped after a release of frog muscle at a constant velocity. Jou rnal of General Physiology 73, 453-467). It appears that studying the histo ry dependence of force production under more functionally relevant conditio ns than has been done to date may provide new information that contributes to our understanding of possible mechanisms associated with force depressio n and force enhancement following muscular length changes, (C) 2000 Elsevie r Science Ltd. All rights reserved.