Disuse of the musculo-skeletal system in space and on earth

Abstract

Muscle mass and strength are well known to decline in response to actual and simulated microgravity exposure. However, despite the considerable knowledge gained on the physiological changes induced by spaceflight, the mechanisms of muscle atrophy and the effectiveness of in-flight countermeasures still need to be fully elucidated. The present review examines the effects and mechanisms of actual and simulated microgravity on single fibre and whole muscle structural and functional properties, protein metabolism, tendon mechanical properties, neural drive and reflex excitability. The effects of inflight countermeasures are also discussed in the light of recent advances in resistive loading techniques, in combined physical, pharmacological and nutritional interventions as well as in the development of artificial gravity systems. Emphasis has been given to the pioneering work of Pietro Enrico di Prampero in the development of artificial gravity systems and in the progress of knowledge on the limits of human muscular performance in space.

Skeletal muscle adaptations to physical inactivity and subsequent retraining in young men

“…In addition, this model offers the advantage of confining atrophy to the musculoskeletal system of the unloaded limb. Reported reductions in KE torque in response to ULLS range 15% to 21 % for durations of 14 to 28 days, 19% for mid-term, 15-28 days, and 21% for long-term, 28+ days, ULLS (Narici and De Boer, 2011).…”

“…Deficits in skeletal muscle mass and function are primary outcomes of chronic unloading, with antigravity muscles such as the knee extensors (KE) being particularly affected (Narici and De Boer 2011). An extensive knowledge of these adverse conditions is paramount, for they are inevitably linked to clinical situations such as prolonged best rest or the use of crutches due to bone fracture or musculoskeletal injury.…”

“…Reported decreases in muscle size, represented by both anatomical cross sectional area (ACSA) and muscle volume of the quadriceps femoris muscle, average about 10% following 10 days to 5 weeks of ULLS, or approximately 2.6% per week (Narici and De Boer, 2011). The disuse-induced loss of muscle strength far exceeds that of muscle mass, indicating the contribution of other factors, such as neural drive, changes in muscle architecture (De Boer et al 2007) and a decrease in single fibre specific tension (D'Antona et al, 2003).…”

“…In addition, this model offers the advantage of confining atrophy to the musculoskeletal system of the unloaded limb. Reported reductions in KE torque in response to ULLS range 15% to 21 % for durations of 14 to 28 days, 19% for mid-term, 15-28 days, and 21% for long-term, 28+ days, ULLS (Narici and De Boer, 2011).Reported decreases in muscle size, represented by both anatomical cross sectional area (ACSA) and muscle volume of the quadriceps femoris muscle, average about 10% following 10 days to 5 weeks of ULLS, or approximately 2.6% per week (Narici and De Boer, 2011). The disuse-induced loss of muscle strength far exceeds that of muscle mass, indicating the contribution of other factors, such as neural drive, changes in muscle architecture (De Boer et al 2007) and a decrease in single fibre specific tension (D'Antona et al, 2003).…”

Potential exercise countermeasures to attenuate skeletal muscle deterioration in space

“…Narici & Boer (2011) 37 Resistance exercise is presently the method of choice for mitigating or even preventing the negative effects of unloading on skeletal muscle. However, the application of artificial gravity with intensive (90% of maximum heart rate) aerobic training have been found to maintain muscle size during simulated microgravity (bed rest).…”