Unilateral lower limb suspension does not mimic bed rest or spaceflight effects on human muscle fiber function

Méthode de simulation de l'atrophie musculaire des spationautes, par suspension d'une jambe, permettant au sujet une activité quotidienne normale avec des béquilles, sans prendre appui sur cette jambe. Cette méthode semble provoquer des altérations cellulaires et des lésions musculaires plus importantes lors de la réambulation

Comparison of a space shuttle flight (STS-78) and bed rest on human muscle function

Effets et comparaison sur les caractéristisques musculaires (longueur, composition des fibres musculaires et les caractéristiques contractiles in vivo du muscle du mollet) de 4 hommes ayant séjournés dans une station orbitale pendant 17 jours et de 8 hommes ayant subi volontairement une immobilisation en position couchée de 17 jours

Comparison of a space shuttle flight (STS-78) and bed rest on human muscle function

Effets et comparaison sur les caractéristisques musculaires (longueur, composition des fibres musculaires et les caractéristiques contractiles in vivo du muscle du mollet) de 4 hommes ayant séjournés dans une station orbitale pendant 17 jours et de 8 hommes ayant subi volontairement une immobilisation en position couchée de 17 jours

Thin filament diversity and physiological properties of fast and slow fiber types in astronaut leg muscles

Slow type I fibers in soleus and fast white (IIa/IIx, IIx), fast red (IIa), and slow red (I) fibers in gastrocnemius were examined electron microscopically and physiologically from pre- and postflight biopsies of four astronauts from the 17-day, Life and Microgravity Sciences Spacelab Shuttle Transport System-78 mission. At 2.5-µm sarcomere length, thick filament density is ~1,012 filaments/µm2 in all fiber types and unchanged by spaceflight. In preflight aldehyde-fixed biopsies, gastrocnemius fibers possess higher percentages (~23%) of short thin filaments than soleus (9%). In type I fibers, spaceflight increases short, thin filament content from 9 to 24% in soleus and from 26 to 31% in gastrocnemius. Thick and thin filament spacing is wider at short sarcomere lengths. The Z-band lattice is also expanded, except for soleus type I fibers with presumably stiffer Z bands. Thin filament packing density correlates directly with specific tension for gastrocnemius fibers but not soleus. Thin filament density is inversely related to shortening velocity in all fibers. Thin filament structural variation contributes to the functional diversity of normal and spaceflight- unloaded muscles

Functional properties of slow and fast gastrocnemius muscle fibers after a 17 day spaceflight

Les effets d'un séjour en apesanteur sur les propriétés contractiles des fibres musculaires rapides et lentes des muscles jumeaux de la jamb

Early structural adaptations to unloading in the human calf muscles

AIM: The present study investigated the influence of muscle architectural changes on muscle torque during 3-week unilateral lower limb suspension (ULLS). METHODS: Plantarflexion maximal voluntary contraction (MVC), soleus (SOL), gastrocnemius medialis (GM) and lateralis (GL) muscle volume (VOL), GL fascicle length (L(f)) and pennation angle (theta), physiological cross-sectional area (PCSA), and electromyographic (EMG) activity were assessed in eight healthy men (aged 19 +/- 0 years) after days 14 and 23 of ULLS. RESULTS: After 14 day of ULLS, MVC and SOL EMG decreased (P < 0.05) by 10% and 29%, respectively, but did not further decline between days 14 and 23. SOL, GM and GL muscle VOL decreased by 5%, 6% and 5%, respectively (P < 0.05), on day 14, and by 7% (SOL), 10% (GM) and 6% (GL) on day 23. In GL, theta and L(f) were reduced by 3% (P < 0.05) and 2% (NS), respectively, on day 14, and by 5% (P < 0.05) and 4% (P < 0.05), respectively, on day 23. Consequently, GL PCSA declined by 3% (P < 0.05) on day 14, but did not further decrease on day 23. Similarly, the 7% (P < 0.05) loss in GL force/PCSA observed on day 14 persisted until the end of the unloading period. CONCLUSION: These findings suggest that rapid muscle architecture remodelling occurs with lower limb unloading in humans, with changes occurring within 14 days of weight bearing removal. These adaptations, mitigating the decline in muscle PCSA, might protect from a larger loss of muscle force