Journal of Applied Physiology, Vol 48, Issue 5 770-775, Copyright © 1980 by American Physiological Society
Energy expended during oxygen deficit period of submaximal exercise in man
P. Pahud, E. Ravussin and E. Jequier
Aerobic (MR) and anaerobic (Man) metabolism was determined during the
transition from mild (50 W external work) to heavier exercise (50% VO2max)
in six subjects. The overall exercise efficiency was calculated during the
oxygen deficit period and during steady-state exercise. MR was obtained by
indirect calorimetry and Man by solving the heat balance equation: MR + Man
- S = (R + C + E) + W, where radiative, convective, and evaporative heat
losses (R + C + E) were measured by direct calorimetry, work output (W) by
ergometry, and heat storage (S) by thermometry. (MR + Man) during the
oxygen deficit period was found to be lower than MR during steady state. In
the 1st min of exercise, mean mixed work efficiency (aerobic + anaerobic)
was 33%, which was greater than aerobic efficiency (26.6%) during steady
state. The mean anaerobic efficiency efficiency was 41%. This difference
reflects the fact that the energy released by splitting of preformed
high-energy bonds (i.e., creatine phosphate) is less than the energy
released when high-energy bonds expended during mechanical work are
continuously regenerated through oxidative phosphorylation. The reported
measurements of overall energy metabolism in man provide means for
estimating in vivo the coupling efficiency of physical work (i.e., 41%) as
well as the efficiency with which energy released by substrate oxidations
is recovered in the form of high-energy bonds (i.e., phosphorylation
efficiency = 64%).
