Walking Energetics, Fatigability, and Fatigue in Older Adults: The Study of Energy and Aging Pilot

Background. Slow gait speed increases morbidity and mortality in older adults. We examined how preferred gait speed is associated with energetic requirements of walking, fatigability, and fatigue. Methods. Older adults (n = 36, 70-89 years) were categorized as slow or fast walkers based on median 400-m gait speed. We measured VO2 peak by graded treadmill exercise test and VO2 during 5-minute treadmill walking tests at standard (0.72 m/s) and preferred gait speeds. Fatigability was assessed with the Situational Fatigue Scale and the Borg rating of perceived exertion at the end of walking tests. Fatigue was assessed by questionnaire. Results. Preferred gait speed over 400 m (range: 0.75-1.58 m/s) averaged 1.34 m/s for fast walkers versus 1.05 m/s for slow walkers (p <.001). VO2 peak was 26% lower (18.5 vs 25.1 ml/kg/min, p =.001) in slow walkers than fast walkers. To walk at 0.72 m/s, slow walkers used a larger percentage of VO2 peak (59% vs 42%, p <.001). To walk at preferred gait speed, slow walkers used more energy per unit distance (0.211 vs 0.186 ml/kg/m, p =.047). Slow walkers reported higher rating of perceived exertion during walking and greater overall fatigability on the Situational Fatigue Scale, but no differences in fatigue. Conclusions. Slow walking was associated with reduced aerobic capacity, greater energetic cost of walking, and greater fatigability. Interventions to improve aerobic capacity or decrease energetic cost of walking may prevent slowing of gait speed and promote mobility in older adults.