to the editor: Muscular efficiency is a typical topic of traditional exercise physiology, but the results of seemingly simple approaches may be misinterpreted. There is a variety of pitfalls that have to be avoided during efficiency determination (e.g., Ref. 1). This is rather simple during cycling, because it is an uncomplicated movement mastered by nearly everybody; furthermore the amount of negative exercise is minimal, but pedaling frequency has to be standardized for comparisons. When using O2 consumption and CO2 production for energy turnover measurements (indirect calorimetry), anaerobic metabolism has to be minimal. This is the case during the steady state of moderate exercise with constant lactic acid concentration; for other conditions oxygen debt has to be measured. For comparisons between subjects either loads with equal work rates have to be used or an efficiency measure that is not dependent on power has to be calculated. Surprisingly Hopker et al. (3) did not consider some obvious traps.
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