The LunHab project: Muscle and bone alterations in male participants following a 10 day lunar habitat simulation

Abstract

New Findings What is the central question of this study?It is well established that muscle and bone atrophy in conditions of inactivity or unloading, but there is little information regarding the effect of a hypoxic environment on the time course of these deconditioning physiological systems. What is the main finding and its importance?The main finding is that a horizontal 10 day bed rest in normoxia results in typical muscle atrophy, which is not aggravated by hypoxia. Changes in bone mineral content or in metabolism were not detected after either normoxic or hypoxic bed rest. Abstract Musculoskeletal atrophy constitutes a typical adaptation to inactivity and unloading of weightbearing bones. The reduced‐gravity environment in future Moon and Mars habitats is likely to be hypobaric hypoxic, and there is an urgent need to understand the effect of hypoxia on the process of inactivity‐induced musculoskeletal atrophy. This was the principal aim of the present study. Eleven males participated in three 10 day interventions: (i) hypoxic ambulatory confinement; (ii) hypoxic bed rest; and (iii) normoxic bed rest. Before and after the interventions, the muscle strength (isometric maximal voluntary contraction), mass (lean mass, by dual‐energy X‐ray absorptiometry), cross‐sectional area and total bone mineral content (determined with peripheral quantitative computed tomography) of the participants were measured. Blood and urine samples were collected before and on the 1st, 4th and 10th day of the intervention and analysed for biomarkers of bone resorption and formation. There was a significant reduction in thigh and lower leg muscle mass and volume after both normoxic and hypoxic bed rests. Muscle strength loss was proportionately greater than the loss in muscle mass for both thigh and lower leg. There was no indication of bone loss. Furthermore, the biomarkers of resorption and formation were not affected by any of the interventions. There was no significant effect of hypoxia on the musculoskeletal variables. Short‐term normoxic (10 day) bed rest resulted in muscular deconditioning, but not in the loss of bone mineral content or changes in bone metabolism. Hypoxia did not modify these results.

The influence of a sustained 10‐day hypoxic bed rest on cartilage biomarkers and subchondral bone in females: The FemHab study

“…The time course of this bone loss during bed rest experiments is approximately 0.5% per week of inactivity (Berg et al, ; Iwamoto, Takeda, & Sato, ; Ohshima, ). We have previously reported in male participants no change in bone mineral content (BMC) of the tibia or femur (McDonnell, Eiken, Frings‐Meuthen, Rittweger, & Mekjavic, ). The short timeline of the physiological withdrawal of mechanical loading is likely insufficient for us to observe with an imaging technique, any structural changes in the bone density or content following the functional alterations.…”

Do females and males exhibit a similar sarcopenic response as a consequence of normoxic and hypoxic bed rest?

“…The schedule is agreed with all participating scientists in order to reduce an interaction effect from each investigation. A similar experimental design for the LunHab (male) study was reported previously (McDonnell et al, 2019) the individual's exercising HR response was within the targeted range and to monitor the S pO 2 levels, respectively. Calculation of the targeted exercise intensity and exercise has been described previously in greater detail (McDonnell, Eiken, Mekjavic, & Mekjavic, 2014).…”

“…Figure 1presents an overview of all of the experimental investigations that took place under the umbrella of the FemHab bed rest research programme to elucidate the scale and experiment interaction of typical bed rest studies. A similar graphical presentation of the experimental schedule for the LunHab study has previously been reported(McDonnell et al, 2019). The participants entered each campaign in a sequential and fixed order with two participants entering each day.…”

Physiological discoveries abound within NASA samples

“…loss of skeletal muscle mass, bone demineralisation, haemodynamic changes, etc.) (see Norsk p. 40;Rittweger, Frings-Meuthen, 2013;McDonnell et al, 2019). Safe return to Earth's gravitational field relies on the prevention of these potentially harmful adaptations.…”