Energy-saving walking mechanisms in obese adults

Energy-saving mechanisms are used in human walking. In obese adults the energy cost of walking (C_w) is higher compared with normal-body mass adults. However, the biomechanical factors involved in this extra cost should result in a higher C_w. The aim of this study was to compare energy-saving walking mechanisms [i.e., mechanical energy saved via pendulum (Recovery) and maximum possible elastic energy usage (MPEEu)] and their influence on C_w in obese vs. lean individuals. The net C_w (NetC_w), external work (W_ext), Recovery, MPEEu, and gait weight transfer duration (gWT) were computed for 13 lean [L; body mass index (BMI) 21.9 ± 1.5 kg/m²] and 13 obese (O; BMI 33.8 ± 2.5 kg/m²) individuals during treadmill walking at five speeds (0.56, 0.83, 1.11, 1.39, 1.67 m/s). No significant difference was found between groups in relative (per kg of body mass) NetC_w (P = 0.13). Relative positive W_ext was significantly lower at the three fastest speeds (P ≤ 0.003) whereas Recovery was higher at the two fastest speeds (P ≤ 0.01) in O than in L individuals. MPEEu tended to be lower in O than in L (P = 0.06), with significantly lower values in O compared with L at 1.39 and 1.67 m/s (P ≤ 0.017). gWT was significantly shorter in O than in L individuals at 1.67 m/s (P = 0.001). The present results reveal that obese adults rely more on the pendular mechanism than on the storage and release of elastic energy for decreasing the amount of positive W_ext and thus limiting the increase in the relative NetC_w. NEW & NOTEWORTHY We observed that obese individuals had a lower maximum possible elastic energy usage per kilogram of body mass than their lean counterparts and they may rely more on the pendular mechanism of walking than on the storage and release of elastic energy for decreasing the external mechanical work and thus limiting the increase in the relative net energy cost of walking.