Can activation account for 80% of skeletal muscle energy use during isometric contraction?

Abstract

presence of a submaximal dose of dantrolene (an inhibitor of the skeletal muscle Ca 2 -release channel), tetanic force was reduced to 36% of its “control” value. Nevertheless, activation heat still accounted for only 42% of the total heat liberated. iv) The idea that 20% of isometric energy turnover is due to cross-bridge cycling is incompatible with the known mechanical performance of fast-twitch muscles. If cross bridges account for only 20% of energy use, then the rate of ATP splitting per cross bridge must be one-quarter the value previously assumed. Maintenance of a high isometric force, in any cross-bridge scheme that requires a low rate of turnover, can be achieved only by reducing the rate of cross-bridge detachment. However, a low detachment rate is inconsistent with the rapid force dynamics and the flat force-velocity curve characteristic of EDL muscles (2). Zhang et al. (5) offer no mechanistic explanation for their result but suggest that it differs from previous data due to an effect of species or temperature or as a result of using submaximal activation. Points i and iii above argue against an effect of either species or temperature, and the dantrolene experiments (point iii) counter the idea that activation costs are higher at submaximal levels of activation.