Normalized economical speed is influenced by aging and not by exercise habituation

Objective: A U-shaped relationship between energy cost of walking ( C w ; J·kg -1 ·m -1 ) and walking speed indicates that there is a specific speed minimizing the C w , called economical speed (ES). It is mostly slower in older adults than young adults; however, effects of leg length on the ES have been ignored. We investigated the effects of aging and exercise habituation on the normalized ES by the leg length (nor-ES). Moreover, the diversity in the stride length (SL) and step frequency (SF) against sinusoidal speed change (SSC) at 30-s and 180-s periods with ±0.56 m･s -1 among sedentary young (SY), active young (AY), and active elderly (AE) adults was also quantified. Results: : The ES was significantly faster in the following sequence: AY, SY, and AE, whereas nor-ES was faster in the AY and SY than in the AE (no difference was found between AY and SY). Delayed SL and preceding SF were observed at the 180-s SSC in the young adults only. Collectively, greater delay and/or precedence of SL-SF combinations against SSC may reflect locomotive flexibility for passive speed change during walking. The nor-ES was slowed by aging; however, it was not influenced by exercise habituation, at least, in young populations.