Muscular efficiency during steady rate exercise: effects of speed and work rate

In a comparison of traditional and theoretical exercise efficiency calculations male subjects were studied during steady rate cycle ergometer exercises of 'O', 200, 400, 600, and 800 kgm/min while pedaling at 40,60,80, and 100 rpm. Gross (no base line correction), net (resting metabolism as base line correction), work (unloaded cycling as base line correction), and delta (measurable work rate as base line correction) efficiencies were computed. The result that gross (range 7.5-20.4%) and net (9.8-24.1%) efficiencies increased with increments in work rate was considered to be an artifact of calculation. A linear or slightly exponential relation between caloric output and work rate dictates either constant or decreasing efficiency with increments in work. The delta efficiency (24.4-34.0%) definition produced this result. Due to the difficulty in obtaining O work equivalents, the work efficiency definition proved difficult to apply. All definitions yielded the result of decreasing efficiency with increments in speed. Since the theoretical thermodynamic computation (assuming mitochondrial P/O=3.0 and ΔG=-11.0 kcal/mol for ATP) holds only for CHO, the traditional mode of computation (based upon VO₂ and R) was judged to be superior since R < 1.0. Assuming a constant phosphorylative coupling efficiency of 60%, the mechanical contraction coupling efficiency appears to vary between 41 and 57%.