The effect of the Gravity-Loading Countermeasure Skinsuit (GLCS) upon aerobic exercise performance

The Russian Pingvin suit provides z-axis loading as a microgravity countermeasure to bone and muscle loss, however the loading regime is uncomfortable and poorly tolerated. The Gravity Loading Countermeasure Skinsuit (GLCS) has been devised to comfortably compress the body along the longitudinal axis in a manner analogous to gravity on Earth, via incrementally increasing z-axis fibre tensions from the shoulder to the feet.We sought to test whether GLCS donning affects sub-maximal aerobic exercise performance and resulting VO2max predictions based on the HR-VO2 relationship, as employed on the ISS. Eight subjects (♂5; 28.4±5.9 yrs; 182.6±9.7 cm; and 77.3±8.3 kg) who gave written informed consent to participate were fitted with a custom-fabricated GLCS. Measurements of lactate, heart rate, core temperature, ventilation (VE), O2 consumption (VO2), and CO2 production (VO2) were recorded along with perceived exertion (BORG scale) during 20 min upright and recumbent ergonometry at 75% VO2max (derived from a previous 7 min Astrand-Rhyming sub-maximal cycle protocol), when wearing either the GLCS, or loose fitting gym attire (GYM).VE was increased during exercise [F(8,224) = 7.335; P<0.05] with increments being greater in the recumbent orientation (compared to upright) in both attires. However, irrespective of orientation, VE was greater when donning the GLCS [F(8,224) = 4.341; P<0.05)]. No significant differences in heart rate, lactate, core temperature, or VO2 were associated with attire or orientation. However, predicted VO2max was significantly lower whilst wearing the GLCS compared to GYM, during recumbent cycling (P<0.05), suggestive of HR-VO2 relationship modulation. Perceived exertion (+4), movement comfort (+4), and body control (+3) were all significantly worsened in the GLCS, irrespective of ergometer orientation (P<0.05).Although exercise-load perception and VE were elevated, 75% VO2max remained achievable suggesting that GLCS donning during ergometry is plausible as an aerobic exercise adjunct on Earth and in space. However, the mechanism of heart rate-VO2 dissociation leading to a reduction of predicted VO2max is unclear and warrants further study, including comparison with actual VO2max assessment.