Spaceflight and exposure to microgravity have wide-ranging effects on many systems of the human body. At the European Space Agency (ESA), a physiotherapist plays a key role in the multidisciplinary ESA team responsible for astronaut health, with a focus on the neuromusculoskeletal system. In conjunction with a sports scientist, the physiotherapist prepares the astronaut for spaceflight, monitors their exercise performance whilst on the International Space Station (ISS), and reconditions the astronaut when they return to Earth. This clinical commentary outlines the physiotherapy programme, which was developed over nine longduration missions. Principles of physiotherapy assessment, clinical reasoning, treatment programme design (tailored to the individual) and progression of the programme are outlined.Implications for rehabilitation of terrestrial populations are discussed. Evaluation of the reconditioning programme has begun and challenges anticipated after longer missions, e.g. to Mars, are considered. Key WordsPhysiotherapy; microgravity; spaceflight; astronaut reconditioning; exercise; low back pain 4 IntroductionThe requirements of the human body, in particular the neuro-musculoskeletal system, are very different in space than on Earth. Interestingly, physiological spaceflight data suggest that it is more difficult to return to gravity than to adapt to microgravity conditions (Payne et al 2007). On Earth, the line of gravity normally passes through the ventral part of the L3 vertebral body (Richter & Hebgen, 2006), ensuring optimal load transfer). In microgravity, musculoskeletal adaptations are appropriate to that environment but this has major effects on muscle function and posture. Astronauts move in a predominantly flexed position and the centre of mass shifts posteriorly (Baroni et al, 2001), with increased recruitment of flexor muscles and a loss of extensors (Fitts et al 2001; Fitts et al 2000). A shift of muscle fibres types from tonic (type 1) to phasic (type 2) occurs (Fitts 2001). Graviceptors, which are sensory receptors that contribute to providing a neural representation of the direction of gravity, with respect to the gravity vector (Binder 2009), no longer function in microgravity.The astronaut therefore receives less information about his/her posture and has to rely on vision and feedback from dynamic receptors.Prolonged microgravity has negative effects on muscle strength and endurance, motor control, coordination and balance (Layne et al, 2001), which may place the astronaut at higher risk of injury. In the spine, primarily lumbar, intervertebral discs absorb more water (hyperhydration) than on Earth (Belavy et al 2016), which can be associated with low back pain (LBP) inflight but is short-lived and has been reported in 70% of astronauts without a history of LBP and 100% of those with a history of LBP (Pool-Goodzwaard et al 2015). The effects of microgravity on the intervertebral disc must be considered to allow safe re-loading of the spine postflight, as the astronaut must readapt...

The purpose of this theoretical study was to estimate the effects of body size and countermeasure (CM) exercise in an all-male crew composed of individuals drawn from a height range representative of current space agency requirements upon total energy expenditure (TEE), oxygen (O 2) consumption, carbon dioxide (CO 2) and metabolic heat (H prod) production, and water requirements for hydration, during space exploration missions. Using a height range of 1.50-to 1.90-m, and assuming geometric similarity across this range, estimates were derived for a four-person male crew (age: 40-years; BMI: 26.5-kg/m 2 ; resting VO 2 and VO 2max : 3.3-and 43.4-mL/kg/min) on 30-to 1,080-d missions, without and with, ISS-like CM exercise (modelled as 2 × 30-min aerobic exercise at 75% VO 2max , 6-d/week). Where spaceflight-specific data/equations were not available, terrestrial data/equations were used. Body size alone increased 24-h TEE (+ 44%), O 2 consumption (+ 60%), CO 2 (+ 60%) and H prod (+ 60%) production, and water requirements (+ 19%). With CM exercise, the increases were + 29 to 32%, + 31%, + 35%, + 42% and + 23 to 33% respectively, across the height range. Compared with a 'small-sized' (1.50-m) crew without CM exercise, a 'large-sized' (1.90-m) crew exercising would require an additional 996-MJ of energy, 52.5 × 10 3-L of O 2 and 183.6-L of water, and produce an additional 44.0 × 10 3-L of CO 2 and 874-MJ of heat each month. This study provides the first insight into the potential implications of body size and the use of ISS-like CM exercise upon the provision of life-support during exploration missions. Whilst closed-loop life-support (O 2 , water and CO 2) systems may be possible, strategies to minimize and meet crew metabolic energy needs, estimated in this study to increase by 996-MJ per month with body size and CM exercise, are required. To sustain humans in space requires the construction of a protective habitat and the generation (and maintenance) of environmental conditions consistent with life. Any habitat, be it a transit vehicle, orbital outpost such as the International Space Station (ISS) in Low Earth Orbit, or future surface habitat, must not only protect crewmembers from the near vacuum of space, but also the extremes of temperature and other space-specific risks including radiation and micrometeorites. Furthermore, appropriate 'life-support' must be provided (i.e. oxygen [O 2 ], water and food), in addition to the management/removal of the by-products of human metabolism (carbon dioxide [CO 2 ], water vapour, metabolic heat, urine, and faeces). On ISS, the provision of life-support is achieved through a combination of supply (and regular re-supply) from the ground (e.g. the Russian 'Progress' expendable cargo and SpaceX's 'Dragon' supply vehicles), and a range of on-board technologies that both manage the internal atmosphere and, increasingly, re-use or recycle by-products (e.g. splitting of CO 2 to generate O 2 and partially [70%] efficient recycling of urine for potable water) 1,2. However, future space...

An alternative approach that is particularly suitable for the radiation health risk assessment (HRA) of astronauts is presented. The quantity, Radiation Attributed Decrease of Survival (RADS), representing the cumulative decrease in the unknown survival curve at a certain attained age, due to the radiation exposure at an earlier age, forms the basis for this alternative approach. Results are provided for all solid cancer plus leukemia incidence RADS from estimated doses from theoretical radiation exposures accumulated during long-term missions to the Moon or Mars. For example, it is shown that a 1000-day Mars exploration mission with a hypothetical mission effective dose of 1.07 Sv at typical astronaut ages around 40 years old, will result in the probability of surviving free of all types of solid cancer and leukemia until retirement age (65 years) being reduced by 4.2% (95% CI 3.2; 5.3) for males and 5.8% (95% CI 4.8; 7.0) for females. RADS dose–responses are given, for the outcomes for incidence of all solid cancer, leukemia, lung and female breast cancer. Results showing how RADS varies with age at exposure, attained age and other factors are also presented. The advantages of this alternative approach, over currently applied methodologies for the long-term radiation protection of astronauts after mission exposures, are presented with example calculations applicable to European astronaut occupational HRA. Some tentative suggestions for new types of occupational risk limits for space missions are given while acknowledging that the setting of astronaut radiation-related risk limits will ultimately be decided by the Space Agencies. Suggestions are provided for further work which builds on and extends this new HRA approach, e.g., by eventually including non-cancer effects and detailed space dosimetry.

Recently, an internal jugular venous thrombus was identified during spaceflight, but whether microgravity induces venous and/or coagulation pathophysiology, and thus, an increased risk of venous thromboembolism (VTE) is unclear. Therefore, a systematic (Cochrane compliant) review was performed of venous system or coagulation parameters in actual spaceflight (microgravity) or ground-based analogues in PubMed, MEDLINE, Ovid EMBASE, Cochrane Library, European Space Agency, National Aeronautics and Space Administration, and Deutsches Zentrum für Luftund Raumfahrt databases. Seven-hundred and eight articles were retrieved, of which 26 were included for evaluation with 21 evaluating venous, and five coagulation parameters. Nine articles contained spaceflight data, whereas the rest reported ground-based analogue data. There is substantial variability in study design, objectives and outcomes. Yet, data suggested cephalad venous system dilatation, increased venous pressures and decreased/reversed flow in microgravity. Increased fibrinogen levels, presence of thrombin generation markers and endothelial damage were also reported. Limited human venous and coagulation system data exist in spaceflight, or its analogues. Nevertheless, data suggest spaceflight may induce an enhanced coagulation state in the cephalad venous system, as a consequence of changes in venous flow, distension, pressures, endothelial damage and possibly hypercoagulability.Whether such changes precipitate an increased VTE risk in spaceflight remains to be determined.

To clarify whether exposure to 6 degrees head-down tilt (HDT) leads to alterations in body fluid volumes and responses to a saline load similar to those observed during space flight we investigated eight healthy subjects during a 4-day, 6 degrees HDT and during a time-control ambulatory period with cross-over. Compared with the ambulatory period, HDT was associated with greater urinary excretion of water and sodium (UV, U(Na)V) from 0 to 12 h (cumulated UV 1,781 +/- 154 vs. 1,383 +/- 170 ml, P < 0.05; cumulated U(Na)V 156 +/- 14 vs. 117 +/- 9 mmol, P < 0.05), and with higher plasma atrial natriuretic factor (ANF) at 4 h. Hemoglobin and hematocrit increased over the first 24 h, and blood and plasma volumes were decreased after 48 h of HDT (P < 0.05). Plasma renin activity (PRA) and aldosterone did not differ between the two groups. With prolongation of HDT, UV and U(Na)V returned close to baseline values. On the fourth HDT day, a 30-min infusion of 20 ml/kg isotonic saline was performed, while a large oral water load maintained a high urine output. The ambulatory period experiment was done with the subjects in the acute supine posture. Sodium excreted within 4 h of loading was 123 +/- 8 mmol during HDT vs. 168 +/- 16 mmol during the ambulatory period (P < 0.05). The increase in plasma ANF and decrease in PRA were greater during HDT than during the ambulatory period (ANF 30 +/- 5 vs. 13 +/- 4 pg/ml, P < 0.05; PRA -1.4 +/- 0.4 vs. -0.5 +/- 0.2 ng. ml(-1). h(-1), P < 0.05). Our data suggest that after a 3-day HDT period, thoracic volume receptor loading returns to the level seen in the upright position, leading to blunted responses to volume expansion, compared with acute supine control.