Aerobic Exercise Deconditioning and Countermeasures During Bed Rest

Abstract

Bed rest is a well-accepted model for spaceflight in which the physiologic adaptations, particularly in the cardiovascular system, are studied and potential countermeasures can be tested. Bed rest without countermeasures results in reduced aerobic capacity and altered submaximal exercise responses. Aerobic endurance and factors which may impact prolonged exercise, however, have not been well studied. The initial loss of aerobic capacity is rapid, occurring in parallel with the loss of plasma volume. Thereafter, the reduction in maximal aerobic capacity proceeds more slowly and is influenced by central and peripheral adaptation. Exercise capacity can be maintained during bed rest and may be improved during recovery with appropriate countermeasures. Plasma volume restoration, resistive exercise, orthostatic stress, aerobic exercise, and aerobic exercise plus orthostatic stress all have been tested with varying levels of success. However, the optimal combination of elements-exercise modality, intensity, duration, muscle groups exercised and frequency of aerobic exercise, orthostatic stress, and supplementary resistive or anaerobic exercise training-has not been systematically evaluated. Currently, frequent (at least 3 days per week) bouts of intense exercise (interval-style and near maximal) with orthostatic stress appears to be the most efficacious method to protect aerobic capacity during bed rest. Further refinement of protocols and countermeasure hardware may be necessary to insure the success of countermeasures in the unique environment of space.

Hypercapnia augments resistive exercise‐induced elevations in intraocular pressure in older individuals

“…Currently, ISS astronauts are scheduled for up to 2.5 h day −1 for exercise preparation, execution and clean‐up, which typically includes ∼30 min of aerobic exercise (choice of treadmill or cycle) and ∼45 min of resistive exercise (Moore et al., 2014). The ISS exercise prescriptions are based on the demonstrated efficacy of countermeasures that combat musculoskeletal and cardiovascular deconditioning in bed rest models (Pavy‐Le Traon et al., 2007; Lee, Moore, Everett, Stenger, & Platts, 2010; Ploutz‐Snyder et al., 2014; Shackelford et al., 2004; Trappe, Burd, Louis, Lee, & Trappe, 2007), and include both continuous and interval aerobic exercise training and resistive exercises, focusing on the trunk and lower body, where the majority of the musculoskeletal losses occur (LeBlanc et al., 2000a,b). However, during this same time period that the ARED came on‐board, ocular structural and functional symptoms began to emerge.…”

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“…Patients admitted with aSAH often have delays in mobilisation due to poor neurological status, awaiting definitive management of the aneurysm or due to aSAH associated symptoms such as headache. It is well known from the literature that prolonged bedrest results in a number of complications that include reduced cardiac output, reduced vascular tone and venous pooling (Lee et al, 2010;Lee et al, 2014). These lead to a reduced ability to respond appropriately to orthostatic changes as patients move into more upright positions and could counteract the medical efforts to prevent DCI and cerebral ischaemia.…”

Towards Integrated Physical Activity Profiling

“…For example, short bouts of intense exercise produce significant metabolic gains without a major impact on total energy expenditure [10]–[12]. Bed rest studies show that even brief bouts of daily activity have the capacity to prevent the unravelling of metabolic homeostasis to sustained inactivity [13]. Epidemiological studies show that sedentary time and breaks in sedentary time may be independently important [14]–[16].…”