The relationship between force depression following shortening and mechanical work in skeletal muscle

Force depression following muscle shortening was investigated in cat soleus (n = 6) at 37 degrees C for a variety of contractile conditions with the a im to test the hypotheses that force depression was independent of the spee d of shortening and was directly related to the mechanical work produced by the muscle during shortening. Force depression was similar for tests in wh ich the mechanical work performed by the muscle was similar, independent of the speed of shortening (range of speeds: 4-256 mm/s). On the other hand, force depression varied significantly at a given speed of shortening but di fferent amounts of mechanical work, supporting the hypothesis that force de pression was not speed - but work dependent. The variations in the mechanic al work produced by the muscle during shortening accounted for 87-96% of th e variance observed in the force depression following shortening further su pporting the idea that the single scalar variable work accounts for most of the observed loss in isometric force after shortening. The results of the present study are also in agreement with the notion that the mechanism unde rlying force depression might be associated with an inhibition of cross-bri dge attachments in the overlap zone formed during the shortening phase, as proposed previously (Herzog and Leonard, 1997. Journal of Bimechanics 30 (9 ). 865-872; Marechal and Plaghki, 1979. Journal of General Physiology 73, 4 53-467). (C) 2000 Elsevier Science Ltd. All rights reserved.