Loss of cardiorespiratory fitness and its recovery following two weeks of head-down bed rest and the protective effects of exercise in 55- to 65-yr-old adults

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.

Impact of 14 Days of Bed Rest in Older Adults and an Exercise Countermeasure on Body Composition, Muscle Strength, and Cardiovascular Function: Canadian Space Agency Standard Measures

“…As shown in Figure 2 , V̇O 2peak levels were maintained in the exercise group and decreased significantly in the control group following the intervention. A detailed description of the results is described in a separate paper [ 25 ].…”

Effects of Posture and Walking on Tibial Vascular Hemodynamics Before and After 14 Days of Head‐Down Bed Rest

“…Participants were randomly allocated into either the control or exercise arm of the study. Those in the exercise arm performed daily exercise activities in the head‐down position throughout HDBR, including high‐intensity interval and aerobic cycling, and upper and lower body resistance training, as previously described, ( 31 , 32 ) whereas those in the control arm received daily passive physiotherapy. Blood was drawn for a full blood count before bed rest and on recovery day 6.…”

Myths and Methodologies: Understanding the health impact of head down bedrest for the benefit of older adults and astronauts. Study protocol of the Canadian Bedrest Study

“…The MUHC research team oversaw the coordination, the steering committee, data management team and other individuals or groups overseeing the trial. Until today, seven paper have been published from this trial including data of the Canadian Space Agency standard measures and other parameters on bone vascularization, cognitive function, baroreflex, cardiovascular capacity and so forth (Balbim et al., 2024 ; Blaber et al., 2023 ; Hajj‐Boutros et al., 2023 ; Hedge, Mastrandrea et al., 2023 , Hedge, Vico et al., 2023 ; Mastrandrea et al., 2023 ; Sadeghian et al., 2022 ).…”