Effects of 17-day spaceflight on knee extensor muscle function and size

Abstract

It is generally held that space travelers experience muscle dysfunction and atrophy during exposure to microgravity. However, observations are scarce and reports somewhat inconsistent with regard to the time course, specificity and magnitude of such changes. Hence, we examined four male astronauts (group mean approximately 43 years, 86 kg and 183 cm) before and after a 17-day spaceflight (Space Transport System-78). Knee extensor muscle function was measured during maximal bilateral voluntary isometric and iso-inertial concentric, and eccentric actions. Cross-sectional area (CSA) of the knee extensor and flexor, and gluteal muscle groups was assessed by means of magnetic resonance imaging. The decrease in strength (P<0.05) across different muscle actions after spaceflight amounted to 10%. Eight ambulatory men, examined on two occasions 20 days apart, showed unchanged (P>0.05) muscle strength. CSA of the knee extensor and gluteal muscles, each decreased (P<0.05) by 8%. Knee flexor muscle CSA showed no significant (P>0.05) change. The magnitude of these changes concord with earlier results from ground-based studies of similar duration. The results of this study, however, do contrast with the findings of no decrease in maximal voluntary ankle plantar flexor force previously reported in the same crew.

Effect of 5 weeks horizontal bed rest on human muscle thickness and architecture of weight bearing and non-weight bearing muscles

“…When this factor is removed, for example during actual spaceXight (Antonutto et al 1999;Widrick et al 1999;LeBlanc et al 2000;Adams et al 2003;Tesch et al 2005) or ground-based models such as immobilisation (Sargeant et al 1977;Narici and Cerretelli 1998), lower limb suspension (Berg et al 1991;Hather et al 1992;Berry et al 1993;Adams et al 1994;de Boer et al 2007a), or bed rest Kawakami et al 2001;Reeves et al 2002;Alkner and Tesch 2004b;Trappe et al 2004) simulating the eVects of microgravity, the anti-gravity muscles such as the plantarXexors and knee extensors appear to be the most aVected (di Prampero and Narici 2003). The most common and apparent adaptation of skeletal muscle with removal of weight bearing contributing to the decreased mechanical output is a loss of muscle mass reXected in a decreased muscle size (LeBlanc et al 1995;Akima et al 2000;Alkner and Tesch 2004b).…”

Global transcriptome analysis in mouse calvarial osteoblasts highlights sets of genes regulated by modeled microgravity and identifies a “mechanoresponsive osteoblast gene signature”

“…R ecent biomedical studies have provided compelling evidence that weightlessness induces several pathological conditions in astronauts, including immune dysfunctions [Sonnenfeld et al, 2003], cardiovascular problems [Tuday et al, 2007], muscle atrophy [Tesch et al, 2005], and skeletal alterations eventually leading to a decrease of bone mass and bone demineralization [Van Loon et al, 1995;Collet et al, 1997;Carmeliet and Bouillon, 1999;CaillotAugusseau et al, 1998CaillotAugusseau et al, , 2000. Indeed, it has been estimated that 1-2% site-specific bone loss occurs in the human skeleton each month during spaceflight [Tilton et al, 1980], and the severity of this phenomenon directly correlates with flight duration [Bikle and Halloran, 1999].…”

High sodium chloride intake exacerbates immobilization-induced bone resorption and protein losses

“…travelers as well as in immobilized subjects, are associated with alterations in protein turnover (1,2,11,15,41,44,66). Specific disuse-induced changes include a negative nitrogen balance, a decrease in whole body protein synthesis, and an increase in lower-limb proteolysis leading to decreased amounts of contractile protein in skeletal muscle (11,20,44,57,67).…”