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

• Published in: Journal of applied physiology (1985) Vol. 123; no. 4; pp. 790 - 799
• Main Authors: Ried-Larsen, Mathias, Aarts, Hugo M, Joyner, Michael J
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.10.2017
• Subjects: Age; Bed Rest; Body Composition; Body mass; Body size; Body weight; Cardiorespiratory Fitness; Circulatory system; Complications; Effects; Humans; Immobilization; Lean body mass; Meta-analysis; Oxygen; Oxygen Consumption; Oxygen uptake; Physical activity; Physical fitness; Pregnancy; Pregnancy complications; Respiratory system; Rest; Reviews; Space Flight; Systematic review; microgravity; spaceflight; cardiorespiratory fitness; exercise test; bed rest
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00415.2017

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.