<p>Study Protocol.</p>

The HIW group targeted 70% of heart rate maximum (HRmax), while the CSW group walked at self-selected speeds below 60% HRmax. Supervised walking sessions were 45 minutes, three times per week, for 16 weeks. The primary outcome was improvement by at least one frailty category on the SHARE-FI (Survey of Health Among Retired Europeans – Frailty Index).

Secondary outcomes included the Timed Up and Go, Short Physical Performance Battery, Berg Balance Scale, and 6-Minute Walk Test (6MWT), measured at baseline and 16 weeks. Participants had a mean (SD) age of 79.2 (8.0) years; 79% were female, and 75% were non-Hispanic White. Improvement in frailty category occurred in 32 of 46 (69.6%) HIW participants versus 26 of 56 (46.4%) CSW participants (OR = 2.91, 95% CI 1.19–7.13, p = 0.02).

HIW participants showed greater gains in gait speed (mean difference = 0.08 m/s, 95% CI 0.03–0.13, p = 0.036) and 6MWT distance (mean difference = 48.99 m, 95% CI 21.1–76.9, p = 0.0088). Mean HRmax was 71% in HIW vs. 59% in CSW (p < 0.001). Median completed sessions were similar (HIW = 35; CSW = 36; p = 0.07).

This cluster-randomized trial demonstrates that high-intensity walking can reverse frailty more effectively than casual-speed walking due to increased physiologic stimuli during more intensive activity. This study is registered at ClinicalTrials.gov ID NCT03654807 (<a href="clinicaltrials.gov/study/NCT03709251" target="_blank">clinicaltrials.gov/study/NCT03709251</a>) Registered 10/12/2018.</p></div>