Comparisons of energy cost and economical walking speed at various gradients in healthy, active younger and older adults

Abstract

Background/objective: Oxygen consumption during walking per unit distance (C_w ; mL/kg/m) is known to be greater for older adults than younger adults, although its underlying process is controversial.

Methods: We measured the C_w values at six gait speeds from 30 m/min to 105 m/min on level ground and gradient slopes (±5%) in healthy younger and older male adults. A quadratic approximation was applied for a relationship between C_w and gait speeds (v; m/min). It gives a U-shaped C_w -v relationship, which includes a particular gait speed minimizing the C_w , the so-called economical speed (ES). The age-related difference of the C_w -v relationship was assessed by comparisons of ES and/or C_w .

Results: A significantly greater C_w at 30 m/min and slower ES were found for older adults at the downhill gradient, suggesting that a combination of leftward and upward shifts of the C_w -v relationship was found at that gradient. Only a slower ES was found for older adults at the uphill gradient, suggesting that a leftward shift was found for older adults at that gradient. Neither a significant leftward nor an upward shift was found at the level gradient. Leg length significantly correlated to the ES for younger adults at the level and downhill gradients, while such a significant relationship was observed only at the level gradient for older adults. The maximal quadriceps muscle strength significantly correlated to the ES for older adults at all gradients, but not for younger adults.

Conclusion: The age-related alteration of the C_w -v relationship depends on the gradient, and its related factors were different between age groups.

Keywords: Aging; Bipedal locomotion; Gait; Optimal speed; Oxygen consumption.

Figure 1

Schematic illustration of (A) upward shift, (B) leftward shift, and (C) combination of upward and leftward shifts of the C_w–gait speed (v) relationship. Y and O represent younger and older adults, respectively. Arrows mean potential shifting directions. C_w–v = oxygen consumption during walking per unit distance and gait speeds.

Figure 2

Oxygen consumption of walking (C_w) in younger and older adults at each gradient. ○: level in younger adults; ●: level in older adults; △: downhill in younger adults; ▲: downhill in older adults; □: uphill in younger adults; and ■: uphill in older adults. * p < 0.05 between younger and older adults at a gait speed of 30 m/min at the downhill gradient. Values are mean ± standard error of the mean.