Cardiorespiratory and Neuromuscular Demand of Daily Centrifugation: Results From the 60-Day AGBRESA Bed Rest Study

Abstract

Purpose: Long stays in space require countermeasures for the degrading effects of weightlessness on the human body, and artificial gravity (AG) has been proposed as an integrated countermeasure. The aim of this study was to assess the cardiorespiratory and neuromuscular demand of AG elicited via daily centrifugation during 60 days of bed rest. Methods: Twenty four participants (33 ± 9 y, 175 ± 9 cm, 74 ± 10 kg, 8 female) were subjected to 60 days of strict six-degree head-down tilt (HDT) bed rest and were randomly allocated to one of three experimental groups: 30 min of daily centrifugation with an acceleration of 1 g at the center of mass and 2 g at the feet applied continuously (cAG) or intermittently in 6 epochs of 5 min each, separated by 3 min breaks (iAG), or non-centrifuged control (CTRL). Cardiorespiratory demand during centrifugation was assessed at the beginning (HDT3) and end (HDT60) of the bed rest phase via spirometry and heart rate monitoring, leg muscle activation was monitored via electromyography. Results: On average, analyses of variance revealed that heart rate during centrifugation increased by 40% (iAG) and 60% (cAG) compared to resting values (p < 0.001), while oxygen uptake did not change significantly (p = 0.96). There was a preference for calf over knee extensor muscle activation (active time soleus 57 ± 27%, gastrocnemius medialis 45 ± 27% and vastus lateralis 27 ± 27%, p < 0.001), with large inter-individual differences in leg muscle active time. AG could not prevent the increase in resting heart rate after bed rest. For most of the recorded parameters, there were little differences between cAG and iAG, with the increase in heart rate during centrifugation being a notable exception (greater increase for cAG, p = 0.01). Conclusion: Daily 30 min bouts of artificial gravity elicited by centrifugation put a substantial demand on the heart as a pump without increasing oxygen consumption. If centrifugation is to be used as a countermeasure for the deteriorating effects of microgravity on physical performance, we recommend combining it with strenuous exercise.

Daily 30-min exposure to artificial gravity during 60 days of bed rest does not maintain aerobic exercise capacity but mitigates some deteriorations of muscle function: results from the AGBRESA RCT

“…Furthermore, we observed that recovery from the exhaustive cycling protocol was severely impaired in all groups after bed rest, as evidenced by the increased heart rate after the end of the test. We had already reported that the two AG interventions could not prevent an increase in resting heart rate after bed rest either (Kramer et al 2020b ). Furthermore, the analysis of oxygen uptake and muscle activity recordings of the daily 30 min centrifugation sessions had revealed that oxygen demand during centrifugation remained at resting levels and that muscle activity of the lower extremity muscles was rather low for most participants of the present study, with a preference for calf muscle activation (Kramer et al 2020b ).…”

“…Participants were instructed to stay in the supine position during centrifugation, to maintain the gaze fixed on a point, to avoid head movements and to contract exclusively the lower extremity muscles to avoid presyncopal symptoms. As there were considerable differences in centrifugation tolerance, this latter instruction resulted in some participants not contracting their muscles beyond normal background activity, while others were using the muscle pump almost constantly (Kramer et al 2020b ). Participants in the two intervention groups (cAG and iAG) completed one daily session of 30 min of centrifugation, either continuously for cAG (1 × 30 min) or intermittently with 6 × 5 min bouts interspersed with 3-min breaks for iAG.…”

“…Rotational speed and the participant's position with respect to the centre of rotation were individually adjusted to achieve an acceleration of 1 g at the estimated centre of mass and approximately 2 g at the feet. The figure was first published in (Kramer et al 2020b ) …”

Limited Effect of 60-Days Strict Head Down Tilt Bed Rest on Vascular Aging

“…Furthermore, the cardiovascular adaptation to HDTBR was not affected by daily artificial gravity training. Other analyses from AGBRESA also report no relevant influences of the artificial gravity intervention on physiological outcomes (Attias et al, 2020;Hoffmann et al, 2020;Kramer et al, 2020;Ganse et al, 2021;Lecheler et al, 2021). Combining artificial gravity with exercise holds promise for future bed rest studies (Diaz-Artiles et al, 2018).…”

“…Rotation direction was changed daily. A more detailed description of the artificial gravity countermeasure can be found elsewhere (Kramer et al, 2020).…”