Assessment of vertical treadmill running under different levels of simulated gravity, using a vertical treadmill facility with a subject loading system (Avatar)

Kurzfassung

Introduction: Prolonged exposure to microgravity during spaceflights leads to severe deconditioning in the physical performance of astronauts that affects dangerously crew health and safety during mission critical maneuvers. To understand the effectiveness of the existing inflight daily countermeasures, treadmill running in simulated microgravity under different levels of adjusted g-load is compared to usual treadmill running on earth. Methods: For purposes of exercise planning onboard the ISS, the objective of this study was to assess the oxygen uptake under using spiroergometric assessment of men and women (n=26, 8 female and 6 male 20- 30 years; 6 male and 6 female 50-60 years) during running on an horizontal treadmill and on a vertical treadmill under different levels of simulated gravity with the Vertical Treadmill Facility (VTF) and Subject loading system (SLS) from the European Space Agency (ESA) and took place in the Physiology Laboratory of the institute of Aerospace Medicine at the Department of Space physiology at the German Space Center (DLR) in Cologne, Germany. After assessing the maximum oxygen uptake using the Bruce-protocol on the horizontal treadmill, an incremental running protocol on both the vertical and horizontal treadmill was performed in randomized order, starting at a speed of 4 kph and increasing every 4 min by 2.5 kph to a maximum of 19 kph. The runs on the vertical treadmill are performed under 0.3g, 0.6g and 1 g of body weight. Results: 26 Subjects were included with a total of 93 runs (9 of 102 runs excluded). The maximum speed was greater for 0.3g and for 0.6g on the vertical treadmill (P < 0.001, see Table above) than on the horizontal treadmill. By contrast, peak oxygen uptake was greater for the horizontal treadmill than for all conditions on the vertical treadmill (P < 0.001), and so was maximal heart rate (P < 0.05). Conclusion: The reduction in peak oxygen uptake on the vertical treadmill was strikingly similar across the three simulated gravity conditions and cannot be explained by inability to run faster. Rather, gravity-related impediment of gas exchange, or impediment of perfusion in horizontal position can be suspected. If this should be the case, then this would constitute a substantial limitation to exercise in space.