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© 2020, The Author(s). Purpose: The objective of this study was to assess whether artificial gravity attenuates any long-duration head-down 60 bed rest (HDBR)-induced alterations in motor unit (MU) properties. Methods: Twenty-four healthy participants (16 men; 8 women; 26–54 years) underwent 60-day HDBR with (n = 16) or without (n = 8) 30 min artificial gravity daily induced by whole-body centrifugation. Compound muscle action potential (CMAP), MU number (MUNIX) and MU size (MUSIX) were estimated using the method of Motor Unit Number Index in the Abductor digiti minimi and tibialis anterior muscles 5 days before (BDC-5), and during day 4 (HDT4) and 59 (HDT59) of HDBR. Results: The CMAP, MUNIX, and MUSIX at baseline did not change significantly in either muscle, irrespective of the intervention (p > 0.05). Across groups, there were no significant differences in any variable during HDBR, compared to BDC-5. Conclusion: Sixty days of HDBR with or without artificial gravity does not induce alterations in motor unit number and size in the ADM or TA muscles in healthy individuals.

© 2019 Weber et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Moon and Mars are considered to be future targets for human space explorations. The gravity level on the Moon and Mars amount to 16% and 38%, respectively, of Earth's gravity. Mechanical loading during the anticipated habitual activities in these hypogravity environments will most likely not be sufficient to maintain physiological integrity of astronauts unless additional exercise countermeasures are performed. Current microgravity exercise countermeasures appear to attenuate but not prevent 'space deconditioning'. However, plyometric exercises (hopping and whole body vibration) have shown promise in recent analogue bed rest studies and may be options for space exploration missions where resources will be limited compared to the ISS. This paper therefore tests the hypothesis that plyometric hop exercise in hypogravity can generate sufficient mechanical stimuli to prevent musculoskeletal deconditioning. It has been suggested that hypogravity-induced reductions in peak ground reaction force (peak vertical GRF) can be offset by increases in hopping height. Therefore, this study investigated the effects of simulated hypogravity (0.16G, 0.27G, 0.38G, and 0.7G) upon sub-maximal plyometric hopping on the Verticalised Treadmill Facility, simulating different hypogravity levels. Results show that peak vertical GRF are negatively related to simulated gravity level, but positively to hopping height. Contact times decreased with increasing gravity level but were not influenced through hopping height. In contrast, flight time increased with decreasing gravity levels and increasing hopping height (P < 0.001). The present data suggest that the anticipated hypogravity-related reductions of musculoskeletal forces during normal walk

© 2016 IAA The Russian Pingvin suit is employed as a countermeasure to musculoskeletal atrophy in microgravity, though its 2-stage loading regime is poorly tolerated. The Gravity-Loading Countermeasure Skinsuit (GLCS) has been devised to comfortably compress the body via incrementally increasing longitudinal elastic-fibre tensions from the shoulders to the feet. We tested whether the Mk III GLCS was a feasible adjunct to sub-maximal aerobic exercise and resulting VO2Max predictions. Eight healthy subjects (5♂, 28±6 yr) performed cycle ergometry at 75% VO2Max (derived from an Astrand-Rhyming protocol) whilst wearing a GLCS and gym clothing (GYM). Ventilatory parameters, heart rate (HR), core temperature (TC), and blood lactate (BL) were recorded along with subjective perceived exertion, thermal comfort, movement discomfort and body control. Physiological and subjective responses were compared over TIME and between GYM and GLCS (ATTIRE) with 2-way repeated measures ANOVA and Wilcoxon tests respectively. Resultant VO2Max predictions were compared with paired t-tests between ATTIRE. The GLCS induced greater initial exercise ventilatory responses which stabilised by 20 min. HR and TC continued to rise from 5 min irrespective of ATTIRE, whereas BL was greater in the GLCS at 20 min. Predicted VO2Max did not differ with ATTIRE, though some observed differences in HR were noteworthy. All subjective ratings were exacerbated in the GLCS. Despite increased perception of workload and initial ventilatory augmentations, submaximal exercise performance was not impeded. Whilst predicted VO2Max did not differ, determination of actual VO2Max in the GLCS is warranted due to apparent modulation of the linear HR-VO2 relationship. The GLCS may be a feasible adjunct to exercise and potential countermeasure to unloaded-induced physiological deconditioning on Earth or in space.

© 2016 National Strength and Conditioning Association. Effective countermeasures against musculoskeletal deconditioning induced by microgravity and disuse are required. A simple alternative to provision of artificial gravity by centrifugation is compressive axial loading. The Russian "Pingvin" suit was the first wearable suit to apply this concept using bungee cords tethered around the shoulders and feet. However, poor loading characteristics and severe thermal and movement discomfort were reported. The gravity loading countermeasure skinsuit (GLCS) uses a bidirectional weave to generate staged axial loading from shoulders to feet, better mimicking how Earth's gravity induces progressive loading head to foot. The Mk III GLCS's loading was evaluated and tolerability assessed during maximal joint motion, ambulation, and selected strength exercises. Eight subjects (5 male and 3 female; 28 ± 3 years; 179 ± 0.1 cm and 74.8 ± 2.9 kg), having given written informed consent, had an Mk III GLCS individually tailored. Axial loading imparted, body height, joint range of motion (ROM), ambulation, and strength tests (12 repetition maximum) were performed in the GLCS and gym attire, with subjective (rating of perceived exertion, thermal comfort, movement discomfort and body control) ratings recorded throughout. Gravity loading countermeasure skinsuit provided significant axial loading when standing but significantly reduced knee (-13°), spinal (-28°) and shoulder flexion/extension ROM (-34°/-13°), in addition to Sit and Reach (-12.8 cm). No thermal issues were reported but there was an increase in subjective discomfort. Gravity loading countermeasure skinsuit did not significantly impede strength exercise, with the exception of shoulder press. The GLCS (Mk III) demonstrates potential as a countermeasure by providing tolerable, static axial loading. Furthermore, it may serve as an elasticlike strength exercise adjunct, which may have utility as a rehabilitation modality after furt