FORCE, VELOCITY AND ENERGY DYNAMICS OF 9 LOAD-MOVING MUSCLES

Nine architecturally different muscles of the cat's hindlimb were inve stigated with respect to the kinetic energy, the potential energy, and the force variations associated with shortening contractions against gravitational loads. Insight about the energy dynamics of contractile muscle can provide a unifying concept for models of muscle performance capability. In this study, it was found that as contractions shortene d from passive equilibrium against a constant mass load, acceleration and deceleration phases appeared. These phases were associated with mu scular force variations of up to 25% of the mass weight in fast twitch muscles at low loads. In contrast, slow twitch muscles were associate d with less than 10% force variations when shortening against a gravit ational lend. It also was found that optimal loads exist which maximiz e each muscle's ability to impart kinetic and potential energy; these optimal loads tend to be in the mid-force range for highly pennate mus cle and in the low-force range for fusiform muscles. It was concluded that the Kinetic energy provided by each muscle is a small percentage of that calculated from its length-force relationship especially at lo w loads. This study confirms that the efficiency of kinetic energy con version is very low at low lends (gradually improving as the loads inc rease) and thereby substantiates early experiments with heat and metab olic energy. Copyright (C) 1997 Elsevier Science for IPEMB.