The energetics of human locomotion can be studied by calculating mechanical efliciency defined as the ratio of mechanical work performed and the net energy consumed. The efficiency values vary with several factors related not only to human machinery but also to methodological problems in determining either work or net energy cost. Using the method described by Fenn (1930), Cavagna and Kaneko (1977) reported the efficiency values for walking and running were 0.35-0.45 and 0.45-0.70 for level walking and running, respectively. One strong criticism is given to mechanical work determined as the sum of external work (Wext) to accelerate the body and internal work (Wint) performed by limbs around the body's center of mass, because of a possible energy transformation between Wext and Wint. The joint power method by Winter (1979) can be used as an appropriate alternative method. Another serious problem exists in determining energy cost for anaerobic metabolism. The most classical way of measuring oxygen debt (Hill, 1924) may lead to over-estimation, and the value of 1 kcal/kg/km obtained by extrapolation of aerobic metabolism (Margaria, 1963) might cause an under-estimation. There are many other elusive factors such as mechanical energy transfer, elastic energy utilization, the so called 'base-line' problem in metabolism and so on. Although several theories have been presented, it would be a more fruitful approach to obtain experimental data by applying a given method with assumptions. The data we obtained on energetics could contribute to a better understanding of human locomotion.
