Bedrest, frailty and exercise countermeasures: A 14-day head-down tilt study in mid-older aged adults

BACKGROUND: Physical inactivity, particularly bed rest during hospitalisation, has adverse effects on frailty. Head-down tilt bed rest paradigms have been used as models of accelerated aging. Such studies have primarily included younger adults and have not examined frailty. We examined how frailty changes during a 14-day bed rest period and subsequent recovery in healthy mid-older aged adults and investigated whether an exercise countermeasure can mitigate any adverse frailty changes. METHODS: Twenty-two healthy adults aged 55-65 years underwent 14 days of bed rest, followed by 7-days of recovery and follow-ups at 4-weeks and 4-months. Participants were randomised to an exercise or control group. Frailty was assessed using self-reported data at up to 10 timepoints, with four frailty indices (FI) derived from 36 to 95 items. RESULTS: Mean age was 58.4 ± 3.7 years, with low frailty at baseline (healthiest 15th percentile of age and sex-normalised frailty scores based on a representative Canadian sample). Frailty increased during bed rest (0.005/day; 95% CI: 0.001, 0.008), decreased non-linearly during recovery, and did not return to baseline levels (mean: 0.018 ± 0.02) by the 4-month follow-up (0.035 ± 0.03; p = 0.005). There was no time-by-group interaction, however frailty levels were - 0.005 (-0.010, 0.000) lower in the exercise group during recovery. Results were consistent across all FI measures. CONCLUSIONS: Bed rest was associated with increases in frailty that were not fully reversed by four months. Exercise during bed rest could support earlier recovery. These findings highlight the harmful effects of bed rest and the potential role of exercise for hospitalised adults.