Effects of aging and arm swing on the metabolic cost of stability in human walking

Abstract

To gain insight into the mechanical determinants of walking energetics, we investigated the effects of aging and arm swing on the metabolic cost of stabilization. We tested two hypotheses: (1) elderly adults consume more metabolic energy during walking than young adults because they consume more metabolic energy for lateral stabilization, and (2) arm swing reduces the metabolic cost of stabilization during walking in young and elderly adults. To test these hypotheses, we provided external lateral stabilization by applying bilateral forces (10% body weight) to a waist belt via elastic cords while young and elderly subjects walked at 1.3m/s on a motorized treadmill with arm swing and with no arm swing. We found that the external stabilizer reduced the net rate of metabolic energy consumption to a similar extent in elderly and young subjects. This reduction was greater (6-7%) when subjects walked with no arm swing than when they walked normally (3-4%). When young or elderly subjects eliminated arm swing while walking with no external stabilization, net metabolic power increased by 5-6%. We conclude that the greater metabolic cost of walking in elderly adults is not caused by a greater cost of lateral stabilization. Moreover, arm swing reduces the metabolic cost of walking in both young and elderly adults likely by contributing to stability.

Figure 1

Schematic of external lateral stabilizer and step width measurement apparatus. Two lightweight elastic cords attached to a padded belt approximately in alignment with the center of mass when the subject faced straight ahead. Step width was measured by digitizing the medio-lateral positions of heel markers in rear-view video at the instant near mid-stance when the photocell was triggered. Adapted from Donelan et al. (Donelan et al., 2004).

Figure 2

(A) Net metabolic power, (B) step width, and (C) step width variability for young and elderly subjects walking normally (black bars), walking normally while externally stabilized (black with white hatch), walking with no arm swing (white), and walking with no arm swing while externally stabilized (white with black hatch). Values are means for all subjects in each group and error bars represent the standard errors of the means. Elderly subjects walked with greater net metabolic cost (* indicates significant age effect, p < 0.0001 for both arm swing and no arm swing). External stabilization reduced net metabolic power, step width, and step width variability to a similar extent in young and elderly adults (S indicates significant stabilization effect, p < 0.05). Eliminating arm swing increased net metabolic power (α indicates significant arm swing effect, p < 0.05).