POWER AT THE EXPENSE OF EFFICIENCY IN CONTRACTION OF WHITE MUSCLE-FIBERS FROM DOGFISH SCYLIORHINUS-CANICULA

Work and heat production of white myotomal muscle fibres from dogfish were measured during sinusoidal movement (0.71-5.0 Hz) at 12 degrees C . Stimulus phase (stimulus timing relative to movement) and duty cycle (stimulus duration as a fraction of movement cycle duration) were var ied to determine the parameters optimal for power output and for effic iency (work/total energy output). Movements of 0.067 and 0.120L(0) wer e used, where L(0) is the muscle fibre length giving maximum force in an isometric tetanus, At each frequency of movement and duty cycle, th e stimulus phase giving the highest power was the same as that giving the highest efficiency. In contrast, at each frequency and optimal sti mulus phase, the dependence of power on duty cycle was very different from the dependence of efficiency on duty cycle, Power generally incre ased with increasing duty cycle, whereas efficiency decreased. Thus, h igh power can be achieved at the expense of efficiency by adjusting st imulus duty cycle. When stimulus phase and duty cycle were optimized, efficiency was always higher for the larger distance of movement. The efficiency of energy conversion can be maintained at a high level as t he frequency of movement increases from 1.25 to 5.0 Hz.