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Exercise efficiency at low power outputs, energetically comparable to daily living activities, can be influenced by homeostatic perturbations (e.g., weight gain/loss). However, an appropriate efficiency calculation for low power outputs used in these studies has not been determined. Fifteen active subjects (seven females, eight males) performed 14, 5-min cycling trials: two types of seated rest (cranks vertical and horizontal), passive (motor-driven) cycling, no-chain cycling, no-load cycling, cycling at low (10, 20, 30, 40 W), and moderate (50, 60, 80, 100, 120 W) power outputs. Mean delta efficiency was 57% for low power outputs compared to 41.3% for moderate power outputs. Means for gross (3.6%) and net (5.7%) efficiencies were low at the lowest power output. At low power outputs, delta and work efficiency values exceeded theoretical values. In conclusion, at low power outputs, none of the common exercise efficiency calculations gave values comparable to theoretical muscle efficiency. However, gross efficiency and the slope and intercept of the metabolic power vs mechanical power output regression provide insights that are still valuable when studying homeostatic perturbations. [ABSTRACT FROM AUTHOR]

The interaction between fatigue and oxidation has been studied in IN 100,* a cast nickel based su-peralloy tested in laboratory air at 1000 °C. The effect of fatigue cycling on oxidation was studied by quantitative metallography on polished specimens which were oxidized in a furnace and on strain cycled low cycle fatigue specimens. Thickness measurements have shown that matrix oxidation obeys a parabolic kinetics and is strongly enhanced by fatigue cycling. Measurements of oxide spikes have shown that interdendritic oxidation obeys a t kinetics and is weakly affected by cyclic straining. A phenomenological equation was proposed which accounts for this interaction through fatigue induced fracture events in the oxide scale. Analysis of the distribution histograms shows that the actual life to crack initiation is identical to the number of cycles to break the matrix oxide scale in the most critical areas. [ABSTRACT FROM AUTHOR]