Journal of Applied Physiology, Vol 41, Issue 2 136-141, Copyright © 1976 by American Physiological Society
Energetics of isometric exercise in man
P. Cerretelli, A. Veicsteinas, M. Fumagalli and L. Dell'orto
In isometric contractions of the plantar flexors (5-40% of maximal tension,
Tmax), VO2 is linearly related to the force exerted, averaging 2 ml/min-kg
of tension. At tension levels above 5% Tmax the lactic acid contribution to
the overall energy demand is constant at about 20%. Therefore, up to at
least 40% Tmax,-muscle blood flow is not totally occluded, though it is
impaired even at low force levels. Below 5% Tmax no lactic acid (LA)
accumulates in blood. The energy required for the development of the
tension is linearly related to the force exerted up to 33% Tmax, thereafter
increasing disproportionately. In the transition from rest to static
contractions of the plantar and forearm flexors (30 and 40% Tmax,
respectively) VO2 increases initially to 200% of the controls, leveling off
later at 150%. During recovery, VO2 increases up to 200% of the initial
resting level, due to the payment of a large O2 debt, decreasing then with
a t 1/2 of about 30 s. The glycolytic component is relatively more
important in isometric contractions of the forearm than of the plantar
flexors. No LA accumulates in static contractions of the plantar flexors of
5-10 s duration interrupted by equal pauses.
