The role of energetic cost in the age-related slowing of gait speed.

OBJECTIVES: To determine whether slow gait represents a compensatory strategy to reduce the energetic cost of walking with age.

DESIGN: Cross-sectional analysis.

SETTING: Community-dwelling volunteers from the Baltimore Longitudinal Study of Aging (BLSA).

PARTICIPANTS: Four hundred twenty community-dwelling persons aged 32 to 96 (mean 68.1 ± 12.5) who underwent a physical examination, physical function testing, and energy expenditure assessment.

MEASUREMENTS: Energy expenditure per minute (mL/kg/min) and per meter (mL/kg/m) during 2.5 minutes of overground walking at customary speed and usual gait speed over 6 m (m/s) were examined. General linear regression models were used to assess the relationship between customary walking energy expenditure and usual gait speed, adjusted for potential confounders including smoking, medical diagnoses, walking-related pain, and balance difficulty.

RESULTS: Usual gait speed was slower with increasing age after age 65. Energy expenditure per minute during customary walking averaged 13.0 ± 2.8 mL/kg/min and was independent of age (ρ < 0.01, P = .88). In contrast, energy expenditure per meter walked was progressively higher after age 65 (ρ = 0.35, P < .001) and heightened after age 80 (r = 0.57, P < .001), mirroring the observed pattern of usual gait speed. This relationship remained significant after adjusting for multiple impairments and comorbidities.

CONCLUSION: These observations support the hypothesis that slower gait at older ages may reflect a compensatory action to offset the greater energetic cost of walking associated with aging and chronic conditions. Future studies should evaluate the specific mechanisms that contribute to this phenomenon as novel targets for clinical intervention.