Energetics of isometric exercise in man

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Abstract
In isometric contractions of the plantar flexors (5-40% of maximal tension, Tmax), .ovrhdot.VO2 [O2 consumption] is linearly related to the force exerted, averaging 2 ml/min .cntdot. kg of tension. At tension levels above 5% Tmax the lactic acid (LA) contribution to the overall energy demand is constant at .apprx. 20%. 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 LA accumulates in blood. The energy required for tension development is linearly related to the froce 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), .ovrhdot.VO2 increases initially to 200% of the controls, leveling off later at 150%. During recovery, .ovrhdot.VO2 increases up to 200% of the initial resting level, due to the payment of a large O2 debt, decreasing then with a t1/2 of .apprx. 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.