Neuromuscular adaptations during long-term bed rest (original) (raw)
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Effects of long-term spaceflight on mechanical properties of muscles in humans
Journal of Applied Physiology, 2001
The effects of long-term spaceflight (90–180 days) on the contractile and elastic characteristics of the human plantarflexor muscles were studied in 14 cosmonauts before and 2–3 days after landing. Despite countermeasures practiced aboard, spaceflight was found to induce a decrease in maximal isometric torque (17%), whereas an index of maximal shortening velocity was found to increase (31%). In addition, maximal muscle activation evaluated during isokinetic tests decreased by 39%. Changes in musculotendinous stiffness and whole joint stiffness were characterized by means of quick-release movements and sinusoidal perturbations. Musculotendinous stiffness was found to be increased by 25%. Whole joint stiffness decreased under passive conditions (21%), whereas whole joint stiffness under active conditions remained unchanged after spaceflight (−1%). This invariance suggests an adaptive mechanism to counterbalance the decrease in stiffness of passive structures by an increased active sti...
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.
Effect of short-duration spaceflight on thigh and leg muscle volume
Medicine & Science in Sports & Exercise, 2000
Human skeletal muscle probably atrophies as a result of spaceflight, but few studies have examined this issue. Thus, little is known about the influence of microgravity upon human skeletal muscle, nor is it possible to assess the validity of ground based models of spaceflight. This study tested the hypothesis that the magnitude of spaceflight induced muscle atrophy would be a function of flight duration and greater than that of bed rest. Methods: Three astronauts flew 9, 15, and 16 d in space. Volume of the knee extensor (quadriceps femoris), knee flexor (hamstrings, sartorius, and gracilis), and plantar flexor (triceps surae) muscle groups was measured using magnetic resonance imaging before and after spaceflight and during recovery. The volume of each muscle group in each image was determined by multiplying cross-sectional area by slice thickness. These values were subsequently summed to calculate muscle volume. Results: Volume changes in the knee extensor, knee flexor, and plantar flexor muscle groups ranged from Ϫ15.4 to Ϫ5.5, Ϫ14.1 to Ϫ5.6, and Ϫ8.8 to Ϫ15.9%, respectively. Muscle volume decreases normalized by flight duration ranged from 0.62 to 1.04%⅐d Ϫ1. These relative changes appeared to be greater than those that we have reported previously for bed rest (Akima et al., J. Gravitat. Physiol. 4:15-22, 1997). Conclusions: These results suggest that atrophy as a result of at least 2 wk of spaceflight varied among individuals and muscle groups and that the degree of atrophy appeared to be greater than that induced by 20 d of bed rest.
Effects of spaceflight on the musculoskeletal system: NIH and NASA future directions
The FASEB Journal, 1993
Participants reviewed the normalfunction and structure of bone and muscle, as well as independent and interactive responses of these tissues to activity and disuse on Earth and in the microgravity environment of space. They then focused on those future directions of research, summarized in this report, that are relevant to the missions and interests of both agencies. A comprehensive review of the presentations is available from NIAMS.
Microgravity-induced fiber type shift in human skeletal muscle
Prolonged microgravity exposure alters human skeletal muscle by markedly reducing size, function, and metabolic capacity. Preserving skeletal muscle health presents a major challenge to space exploration beyond low Earth orbit. Humans express three distinct pure myosin heavy chain (MHC) muscle fiber types (slow fast: MHC I, IIa, and IIx), along with hybrids (MHC I/IIa, IIa/IIx, and I/IIa/IIx). After reviewing current research, this paper presents evidence for a "slow to fast" microgravity-induced skeletal muscle fiber type shift in humans. Spaceflight and bed rest induce decreased MHC I fiber proportion while increasing fast hybrid types (particularly MHC IIa/IIx fibers). This alteration in muscle cell phenotype negatively impacts performance and induces undesirable metabolic adaptations. While exercise has been postulated to minimize the negative effects of microgravity on human muscle, past spaceflight countermeasures have insufficiently prevented fiber type shifts in hu...
Sarcolab pilot study into skeletal muscle’s adaptation to long-term spaceflight
npj Microgravity, 2018
Spaceflight causes muscle wasting. The Sarcolab pilot study investigated two astronauts with regards to plantar flexor muscle size, architecture, and function, and to the underlying molecular adaptations in order to further the understanding of muscular responses to spaceflight and exercise countermeasures. Two crew members (A and B) spent 6 months in space. Crew member A trained less vigorously than B. Postflight, A showed substantial decrements in plantar flexor volume, muscle architecture, in strength and in fiber contractility, which was strongly mitigated in B. The difference between these crew members closely reflected FAK-Y397 abundance, a molecular marker of muscle’s loading history. Moreover, crew member A showed downregulation of contractile proteins and enzymes of anaerobic metabolism, as well as of systemic markers of energy and protein metabolism. However, both crew members exhibited decrements in muscular aerobic metabolism and phosphate high energy transfer. We conclu...
Sharp Changes in Muscle Tone in Humans Under Simulated Microgravity
Frontiers in Physiology, 2021
A decrease in muscle tone induced by space flight requires a standardized assessment of changes to control the state of the neuromuscular system. This study is a step toward the development of a unified protocol, aimed at determining the initial effect of the presence or withdrawal of support on muscle tone, the effects of a 2-h supportlessness in Dry Immersion (DI) experiments, and the changes in muscle tone depending on the site of measurement. To perform measurements of changes in muscle tone, we used a MyotonPRO device. The list of muscles that we assessed includes: trunk – mm. deltoideus posterior, trapezius, erector spinae; leg – mm. biceps femoris, rectus femoris, tibialis anterior, soleus, gastrocnemius; foot – m. flexor digitorum brevis, tendo Achillis, aponeurosis plantaris. The study involved 12 healthy volunteers (6 men, 6 women) without musculoskeletal disorders and aged 32.8 ± 1.6 years. At the start of DI, there was a significant decrease in muscle tone of the followi...
Adaptation of Mouse Skeletal Muscle to Long-Term Microgravity in the MDS Mission
PLoS ONE, 2012
The effect of microgravity on skeletal muscles has so far been examined in rat and mice only after short-term (5-20 day) spaceflights. The mice drawer system (MDS) program, sponsored by Italian Space Agency, for the first time aimed to investigate the consequences of long-term (91 days) exposure to microgravity in mice within the International Space Station. Muscle atrophy was present indistinctly in all fiber types of the slow-twitch soleus muscle, but was only slightly greater than that observed after 20 days of spaceflight. Myosin heavy chain analysis indicated a concomitant slow-to-fast transition of soleus. In addition, spaceflight induced translocation of sarcolemmal nitric oxide synthase-1 (NOS1) into the cytosol in soleus but not in the fast-twitch extensor digitorum longus (EDL) muscle. Most of the sarcolemmal ion channel subunits were up-regulated, more in soleus than EDL, whereas Ca 2+ -activated K + channels were down-regulated, consistent with the phenotype transition. Gene expression of the atrophy-related ubiquitin-ligases was up-regulated in both spaceflown soleus and EDL muscles, whereas autophagy genes were in the control range. Muscle-specific IGF-1 and interleukin-6 were down-regulated in soleus but up-regulated in EDL. Also, various stress-related genes were up-regulated in spaceflown EDL, not in soleus. Altogether, these results suggest that EDL muscle may resist to microgravity-induced atrophy by activating compensatory and protective pathways. Our study shows the extended sensitivity of antigravity soleus muscle after prolonged exposition to microgravity, suggests possible mechanisms accounting for the resistance of EDL, and individuates some molecular targets for the development of countermeasures.
Neuromuscular Adaptation to Microgravity Environment
The Japanese Journal of Physiology, 2000
The pattern of muscle activity influences the morphological, metabolic, and contractile properties of skeletal muscles. For example, the metabolic capacity of muscles is affected specifically by the type of exercise training [1-3]. Increased activity or overloading by removing the synergists causes a compensatory hypertrophy [4-11]. Hypertrophy is also induced by the stretching of matured muscles in vivo [12, 13] and cultured myotubes and fibroblasts [14-17]. Exercise-induced metabolic adaptation of muscles is lost when exercise training is stopped [18]. Further, muscle atrophy is induced by denervation [10, 19], spinal cord transection [20], joint immobilization [21-23], tenotomy [24, 25], spaceflight [26-29], and/or hindlimb suspension [29-32]. Most of these models are generally presumed to be models of reduced neuromuscular activity. But the level of use may not be the only factor involved in the atrophic process. There is a close association in the physiological, biochemical, and morphological properties between a motoneuron and the muscle fibers it innervates [1]. Studies to support this view are those in which chronic electrical stimulation at low frequency (1-10 Hz) changes the properties of fast-twitch muscles toward those of slow-twitch muscles [33-38]. Some of the characteristics of muscle fibers are also altered following cross-innervation [39-42]. Buller et al. [40] suggested that the neural influence on muscle could be due to neurotrophic effect as well as via nerve impulses. Muscular Responses to Gravitational Unloading Morphological properties Gravitational unloading by exposure to weightlessness [26-29, 43-47] and/or its simulation model, hindlimb suspension [29-32, 48-56], causes rapid atrophy in muscles, such as soleus and adductor longus, that are composed predominantly of slow fibers. The cross-sectional areas (CSAs) of both slow-and fasttwitch fibers of rats were less after 14 d of spaceflight and hindlimb suspension than those in the agematched controls [29]. But the degree of atrophy was greater in slow-than fast-twitch fibers [28, 29]. Therefore, muscles composed of predominantly slow fibers are more susceptible to atrophy [26, 28, 47]. The weights of fast-twitch ankle dorsi-flexors, such as the tibialis anterior (TA) and extensor digitorum longus (EDL), are also generally less after unloading than those of age-matched controls [31, 57]. But these were