Cardiorespiratory fitness declines with age and this decline can be accelerated by inactivity and bed rest. Recovery of fitness is possible, but the timeline in 55-65-year-old adults is unknown. Furthermore,… Click to show full abstract
Cardiorespiratory fitness declines with age and this decline can be accelerated by inactivity and bed rest. Recovery of fitness is possible, but the timeline in 55-65-year-old adults is unknown. Furthermore, the effectiveness of exercise to prevent deconditioning during bed rest is unexplored in this age group. Twenty-two adults (11 women, 59 ± 3 years) completed two weeks of strict 6° head-down bed rest (HDBR). Half of the participants performed approximately 1 hour of daily exercises, including high-intensity interval cycling, aerobic cycling, and upper- and lower-body resistance training, while control participants were inactive. Step-incremental cycling tests to exhaustion were conducted pre-HDBR and at 3 times during the recovery phase (day-1 or 2, day-6, and 4 weeks) to assess peak oxygen uptake (V̇O2). Peak V̇O2 was reduced in the control group throughout the first 6 days of recovery, but did return to pre-HDBR levels by the 4-week recovery time point (interaction: p=0.002). In the exercise group, peak V̇O2 was not different at any time point during recovery from pre-HDBR. Ventilatory threshold V̇O2 (interaction: p=0.002) and heart rate at 15 W (interaction: p=0.055) mirrored the changes in peak V̇O2 in each respective group. Overall, this study showed that approximately 1 hour of daily exercise effectively protected 55-65-year-old adults' cardiorespiratory fitness during two weeks of HDBR. HDBR without exercise countermeasures caused substantial reductions in cardiorespiratory fitness, but fitness recovered within 4 weeks of resuming daily activities. These findings highlight the importance of physical activity in late middle-age adults.
               
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