Effects of strict prolonged bed rest on cardiorespiratory fitness: systematic review and meta-analysis

Abstract

The aim of this systematic review and meta-analysis [International Prospective Register of Systematic Reviews (PROSPERO) CRD42017055619] was to assess the effects of strict prolonged bed rest (without countermeasures) on maximal oxygen uptake (V̇o) and to explore sources of variation therein. Since 1949, 80 studies with a total of 949 participants (>90% men) have been published with data on strict bed rest and V̇o The studies were conducted mainly in young participants [median age (interquartile range) 24.5 (22.4-34.0) yr]. The duration of bed rest ranged from 1 to 90 days. V̇o declined linearly across bed rest duration. No statistical difference in the decline among studies reporting V̇o as l/min (-0.3% per day) compared with studies reporting V̇o normalized to body weight (ml·kg·min; -0.43% per day) was observed. Although both total body weight and lean body mass declined in response to bed rest, we did not see any associations with the decline in V̇o However, 15-26% of the variation in the decline in V̇o was explained by the pre-bed-rest V̇o levels, independent of the duration of bed rest (i.e., higher pre-bed-rest V̇o levels were associated with larger declines in V̇o). Furthermore, the systematic review revealed a gap in the knowledge about the cardiovascular response to extreme physical inactivity, particularly in older subjects and women of any age group. In addition to its relevance to spaceflight, this lack of data has significant translational implications because younger women sometimes undergo prolonged periods of bed rest associated with the complications of pregnancy and the incidence of hospitalization including prolonged periods of bed rest increases with age. Large interindividual responses of maximal oxygen uptake (V̇o) to aerobic exercise training exist. However, less is known about the variability in the response of V̇o to prolonged bed rest. This systematic review and meta-analysis showed that pre-bed-rest V̇o values were inversely associated with the change in V̇o independent of the duration of bed rest. Moreover, we identified a large knowledge gap about the causes of decline in V̇o, particularly in postmenopausal women, which may have clinical implications.

High-Intensity Exercise Mitigates Cardiovascular Deconditioning During Long-Duration Bed Rest

“…This contrast suggests that exercise training might quickly influence the hemodynamic balance, inducing post-exercise hypotension likely due to an early blood volume reduction. We speculate that training might accelerate the loss of plasma volume, as demonstrated by recent works showing that lower limb exercise (cycling) produced a different adaptation of the autonomic sympathetic tone in supine vs. upright position (Ried-Larsen et al, 2017 ). Supine position activated the stretch receptors of heart, veins, and pulmonary circulation, increasing central blood volume, and blunting the metaboreflex activation.…”

“…Such a response reduced heart contractility, limiting SV, and reducing blood pressure via a non-renal mechanism. At the same time, this reaction could be responsible for a reduction in plasma renin activity and therefore for an early increase in water loss (Ried-Larsen et al, 2017 ). Thus, a potential additive effect on the cardiovascular system of acute blood volume changes and sympathetic response to exercise might occur in the first days of training and HDT.…”

Effects of 12 months of detraining on health-related quality of life in patients receiving hemodialysis therapy

“…However, there is a notorious controversy regarding the required absence time from any systematic exercise training to lose all the acquired adaptations. The vast majority of the published studies on "detraining effect" (or reduction in exercise training volume) on physical performance, body composition and skeletal muscle physiology and biochemistry, involved athletes and physically-active populations [28,29], whilst data are available also from bed rest studies [30] and studies on astronauts [31]. Briefly, these findings report significant reductions in cardiorespiratory capacity [29], muscle strength and power, alternations in muscle fiber type (i.e.…”

MNX (Medium Duration Nutrition and Resistance-Vibration Exercise) Bed-Rest: Effect of Resistance Vibration Exercise Alone or Combined With Whey Protein Supplementation on Cardiovascular System in 21-Day Head-Down Bed Rest

“…The decreased VO2max in CON (−17 ± 13%) compared to pre HDBR levels is in line with previous studies of similar duration. A decrease of 1% per day until 30 days of HDBR is usually observed in absence of CM (Convertino, 1996;Watenpaugh et al, 2000), although a smaller reduction of 0.3% per day is reported by Ried-Larsen et al in a recent meta-analysis (Ried-Larsen et al, 2017).…”