Running vs. resistance exercise to counteract deconditioning induced by 90-day head-down bedrest

Abstract

Spaceflight is associated with enhanced inactivity, resulting in muscular and cardiovascular deconditioning. Although physical exercise is commonly used as a countermeasure, separate applications of running and resistive exercise modalities have never been directly compared during long-term bedrest. This study aimed to compare the effectiveness of two exercise countermeasure programs, running and resistance training, applied separately, for counteracting cardiovascular deconditioning induced by 90-day head-down bedrest (HDBR). Maximal oxygen uptake (V˙O2max), orthostatic tolerance, continuous ECG and blood pressure (BP), body composition, and leg circumferences were measured in the control group (CON: n = 8), running exercise group (RUN: n = 7), and resistive exercise group (RES: n = 7). After HDBR, the decrease in V˙O2max was prevented by RUN countermeasure and limited by RES countermeasure (−26% in CON p < 0.05, −15% in RES p < 0.05, and −4% in RUN ns). Subjects demonstrated surprisingly modest orthostatic tolerance decrease for different groups, including controls. Lean mass loss was limited by RES and RUN protocols (−10% in CON vs. −5% to 6% in RES and RUN). Both countermeasures prevented the loss in thigh circumference (−7% in CON p < 0.05, −2% in RES ns, and −0.6% in RUN ns) and limited loss in calf circumference (−10% in CON vs. −7% in RES vs. −5% in RUN). Day–night variations in systolic BP were preserved during HDBR. Decrease in V˙O2max positively correlated with decrease in thigh (r = 0.54 and p = 0.009) and calf (r = 0.52 and p = 0.012) circumferences. During this 90-day strict HDBR, running exercise successfully preserved V˙O2max, and resistance exercise limited its decline. Both countermeasures limited loss in global lean mass and leg circumferences. The V˙O2max reduction seems to be conditioned more by muscular than by cardiovascular parameters.

Comprehensive assessment of physiological responses in women during the ESA dry immersion VIVALDI microgravity simulation

“…Participants showed an 11% increase in first-step heart rate during aerobic test, this could be interpreted as a part of the cardiovascular deconditioning. This is in line with results from spaceflights and bedrest studies, as a multi-system deconditioning appears with cardiac atrophy, hypovolemia, and muscle metabolic changes, all contributing to the reduction in exercise performance 49 – 51 . As a result, microgravity exposure induces an ‘ageing-like’ cardiovascular deconditioning with loss of physical fitness 52 .…”

“…After long-duration spaceflights (>4 months), nearly 80% of astronauts suffer from orthostatic intolerance, and after short-term spaceflights, 20% experience presyncope 44 . During long-term bedrest (>35 days) in men, a high range of participants is considered intolerant to an orthostatic stress by tilt or stand test, from 25% to nearly 60% 45 – 49 . The sample remains however quite small in most of these studies ( n < 10 participants in control groups).…”

Harnessing Passive Pulsatile Shear Stress for Alzheimer’s Disease Prevention and Intervention

“…lation [126] and repeated horizontal jumping [127] in humans. Furthermore, these exercise countermeasures for microgravity are being adapted for use in bedrest studies in older adults [121,128,129]. The application of PPSS in the latter conditions deserves future studies.…”

The Physiology of Neurogenic Obesity: Lessons from Spinal Cord Injury Research

“…In bed rest studies, atrophy in non-exercising people without paralysis approximates 0.1-1% per day [63], depending on the muscle group. For example, in a 90day head-down tilt bed rest study, participants in the sedentary control group had a 10% decrease in wholebody lean mass [64]. While we know of no head-to-head comparison, it seems that the rate and extent of atrophy following SCI substantially exceeds muscle loss due to mechanical unloading alone.…”

“…Furthermore, SCI is a stark example of the primary role resting energy expenditure plays in total daily energy expenditure and thus energy balance. The substantial decreases in muscle mass experienced by PwSCI contribute to low resting metabolic rate in this population [ 66 ], with rates as low as 1,129 ± 300 kcal/day reported in a group of adult men with tetraplegia (involving neurologic insult to the cervical spinal cord) [ 67 ] compared with the expected generalization of 2,000 kcal/day in adult men without SCI [ 68 ]. With a limited capacity to increase exercise energy expenditure due to paralysis [ 69 ], SCI presents a situation where resting metabolic rate is of utmost importance when attempting to understand and/or manipulate an energy balance.…”