The energy cost to maintain isometric tension in fast-twitch EDL was initially threefold greater than in slow-twitch soleus, but diminished to only 50% greater after 12 seconds of stimulation.
The study demonstrates a biochemical energy balance in both slow- and fast-twitch mouse muscles during contraction, with fast-twitch muscles initially having a higher energy cost that diminishes with prolonged stimulation.
The energy utilization associated with contraction was measured in isolated slow- and fast-twitch muscles of the mouse at 20 degrees C. The extent of this utilization was estimated from either the extent of high-energy phosphate splitting occurring during contraction (the initial chemical change, delta approximately P init) or from the extent of recovery resynthesis calculated from the observed oxygen consumption and lactate production occurring during the recovery period (recovery chemical resynthesis, delta approximately P rec). For short tetani, the cost to maintain isometric tension in the fast-twitch extensor digitorum longus (EDL) was approximately threefold greater than that in the slow-twitch soleus. With prolonged stimulation, however, the energy cost in the EDL diminished so that after 12 s of stimulation, the energy cost in the EDL was only 50% greater than that of the soleus. For both the slow-twitch soleus and the fast-twitch EDL and for all tetanus durations (up to 15 s), the extent of the initial chemical change was identical with the amount of recovery chemical resynthesis, showing that a biochemical energy balance existed in these muscles.
Crow et al. (1982) studied Muscle energetics. Fast-twitch extensor digitorum longus (EDL) muscle contraction vs. Slow-twitch soleus muscle contraction was evaluated on Energy utilization associated with contraction (initial chemical change and recovery chemical resynthesis). The energy cost to maintain isometric tension in fast-twitch EDL was initially threefold greater than in slow-twitch soleus, but diminished to only 50% greater after 12 seconds of stimulation.