The apparent efficiency of human muscle varies significantly depending on the exercise modality, driven by the ability to store and re-use elastic energy when a positive exercise phase immediately follows a negative phase.
Abstract 3 subjects ran on the treadmill (10 km/h) against varying horizontal impeding forces. One subject was further studied during the same kind of walking and bicycling on the treadmill, and during work consisting in lowering and lifting the body by flexing and extending the legs from a standing or sitting position at varying frequencies, with or without rebound in the deepest position. Workpower (W kcal/min), and the corresponding steady state metabolic rate (E kcal/min, Douglas bag method) were measured. Apparent efficiency (N) was calculated as Δẁ/ΔÈ× 100 %. During load running N was 53.8, 37.6 and 41.2 %, respectively, in the 3 subjects. In the subject more extensively studied N was: running 53.8, walking 32.3, bicycling 25.1, knee‐flexions (deep or half) with rebound 39.4 or 41.0, without rebound 26.1 or 21.9 %. These variations in N % were explained in accordance with the possibilities for re‐using the energy, absorbed and stored in the muscles as elastic energy during a phase of negative exercise, in a subsequent phase of positive exercise. The condition of this is that the positive phase follows immediately after the negative. A calculation showed that during running 35–53 % of the energy absorbed during the negative phase was re‐used. Corresponding figures for walking and rebounding knee‐extensions were 23 % and 34 %, respectively, while in bicycling and knee‐extensions without rebound all of the negative work degenerated into heat.
Asmussen et al. (Sun,) studied this question.
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