Prolonged space flight-induced alterations in the structure and function of human skeletal muscle fibres

Abstract

The primary goal of this study was to determine the effects of prolonged space flight (∼180 days) on the structure and function of slow and fast fibres in human skeletal muscle. Biopsies were obtained from the gastrocnemius and soleus muscles of nine International Space Station crew members ∼45 days pre-and on landing day (R+0) post-flight. The main findings were that prolonged weightlessness produced substantial loss of fibre mass, force and power with the hierarchy of the effects being soleus type I > soleus type II > gastrocnemius type I > gastrocnemius type II. Structurally, the quantitatively most important adaptation was fibre atrophy, which averaged 20% in the soleus type I fibres (98 to 79 μm diameter). Atrophy was the main contributor to the loss of peak force (P 0 ), which for the soleus type I fibre declined 35% from 0.86 to 0.56 mN. The percentage decrease in fibre diameter was correlated with the initial pre-flight fibre size (r = 0.87), inversely with the amount of treadmill running (r = 0.68), and was associated with an increase in thin filament density (r = 0.92). The latter correlated with reduced maximal velocity (V 0 ) (r = −0.51), and is likely to have contributed to the 21 and 18% decline in V 0 in the soleus and gastrocnemius type I fibres. Peak power was depressed in all fibre types with the greatest loss (∼55%) in the soleus. An obvious conclusion is that the exercise countermeasures employed were incapable of providing the high intensity needed to adequately protect fibre and muscle mass, and that the crew's ability to perform strenuous exercise might be seriously compromised. Our results highlight the need to study new exercise programmes on the ISS that employ high resistance and contractions over a wide range of motion to mimic the range occurring in Earth's 1 g environment.

Masticatory muscles of mouse do not undergo atrophy in space

“…Therefore, fiber-type differences cannot explain the divergent responses to flight. Previous studies investigating the effects of exercise loading on human skeletal muscle during a prolonged (;180 days) exposure to space weightlessness have shown that mass loss in limb muscles is exponential with the duration of flight and that aerobic and low intensity resistance exercise countermeasures fail to adequately protect muscle mass, especially of the antigravity soleus muscle (33,34). The lack of mass loss in MA muscles revealed in this study could be a protective effect, at least for the short period of an ;13 days of space flight, by chewing-induced loading of these muscles, the specific physiological characteristics that masticatory muscles possess, or a combination of both.…”

Stem Cell Health and Tissue Regeneration in Microgravity

“…1). Through these experiments, the detrimental effects of microgravity on cellular function were consistently revealed, including inhibition of osteoblast differentiation [2,32,33], reduced osteoblast numbers [34], atrophy of skeletal muscle cells [14,35,36], impaired activation of immune cells and consequently the immune system [37 -39], abnormal formation of chondrocytes [40], and collapse of the cytoskeleton in T lymphoblastoid cells (Jurkat) [41], thereby displaying the impact of microgravity on various physiological systems.…”

Effect of 23-day muscle disuse on sarcoplasmic reticulum Ca2+ properties and contractility in human type I and type II skeletal muscle fibers

“…IT IS WELL KNOWN that chronic muscle disuse in young healthy adults, as induced by spaceflight, bedrest, or immobilization, adversely affects muscle function. Although the loss of skeletal muscle mass induced by the disuse is widely acknowledged to contribute to this impairment, it has become increasingly evident that contractile dysfunction is disproportionately greater than decrements in cross-sectional area (CSA), as indicated by a decrease of specific force, suggesting a significant role played by decreased muscle "quality" in the dysfunction (4,9,15,33,51). It has been recently reported that the reduction of muscle quality can be attributed to a complex interaction of many factors that can affect neuromuscular transmission (4,24,42), muscle architecture (8,9), muscle fiber phenotype (14,38), and contractile apparatus properties (20,21).…”