Walking Energetics, Fatigability, and Mobility in Older Adults: Study of Muscle, Mobility, and Aging (SOMMA)

Gait speed is a marker of mobility among older adults. Pilot work indicated poorer walking energetics (oxygen consumption during physical tasks) and greater fatigability (standardized measure of fatigue anchored to activity) may contribute to slower gait speed; findings were limited by a small sample and narrow gait speed range. PURPOSE: To examine associations of walking energetics and perceived fatigability with gait speed. METHODS: Participants in SOMMA (N = 849, age = 76.3 ± 5.0 yrs, 58.7% women, 4 m usual-paced gait speed median = 1.01 m/s, range = 0.64-1.83 m/s) completed a 3-stage treadmill cardiopulmonary exercise test to measure oxygen consumption (VO2, mL/kg/min): Stage 1: Preferred walking speed (PWS, usual-paced 400 m walk speed), 5-min bout, 0% grade; Stage 2: Symptom-limited maximal test for peak VO2; Stage 3: Fixed walking speed (FWS, 0.67 m/s), 5-min bout, 0% grade after 20 min rest. Average VO2 from last 3 minutes of PWS and FWS were calculated. Perceived physical fatigability was measured using two METHODS: 1) validated 10-item Pittsburgh Fatigability Scale (PFS, range 0-50; higher = greater fatigability) and 2) Borg Rating of Perceived Exertion (RPE) at end of FWS test (range 6-20; higher = greater exertion). A linear regression model assessed association of VO2peak, PWS VO2, FWS VO2, PFS score, and RPE with gait speed, adjusted for site, age, race, sex, and accelerometry-measured total physical activity. RESULTS: Comparing slower walkers (<1.01 m/s) to faster walkers (≥1.01 m/s), VO2peak (18.3 ± 4.0 vs 22.0 ± 4.9 mL/kg/min) and PWS VO2 (11.7 ± 2.3 vs 13.1 ± 2.5 mL/kg/min) were lower, while PFS scores (18.2 ± 8.4 vs 13.3 ± 8.1) and RPE (9.0 ± 2.1 vs 7.9 ± 1.4) were higher, all p < 0.001. FWS VO2 did not differ by gait speed groups (9.5 ± 1.7 vs 9.4 ± 1.9 mL/kg/min, p = 0.38). Lower VO2peak (β = -0.05), lower PWS VO2 (β = -0.09), higher FWS VO2 (β = 0.08), higher PFS score (β = 0.03), and higher RPE (β = 0.02) were independently associated with slower gait speed after adjustment, all p < 0.001 (β per SD lower). CONCLUSION: Worse walking energetics were independently associated with slower gait speed, potentially due to higher VO2 cost ratio (i.e. % of VO2peak used) at a given speed and working closer to fatigue threshold. Next steps will examine mediating roles of fatigability and VO2 in the mobility pathway. Funded by NIA R01AG059416.