Spaceflight effects on single skeletal muscle fiber function in the rhesus monkey

Area of Science:

• Muscle physiology
• Spaceflight biology
• Animal models

Background:

• Muscle atrophy is a significant concern for astronauts during space missions.
• Understanding cellular changes in muscle fibers under microgravity is crucial for developing countermeasures.
• Rhesus monkeys serve as a relevant model for studying human physiological responses to spaceflight.

Purpose of the Study:

• To investigate the effects of 14 days of weightlessness on cellular properties of slow- and fast-twitch muscle fibers in rhesus monkeys.
• To compare the impact of spaceflight (SF) with a ground control (CS) on muscle fiber characteristics.

Main Methods:

• Analysis of soleus (Sol) type I, medial gastrocnemius (MG) type I, and MG type II muscle fibers.
• Measurement of fiber diameter, peak force, peak fiber stiffness, Ca(2+) sensitivity, and maximal shortening velocity.
• Comparison between vivarium controls, capsule sit (CS) controls, and spaceflight (SF) groups.

Main Results:

• Both CS and SF reduced Sol type I fiber diameter and peak force.
• SF significantly decreased relative force (kN/m(2)) in Sol type I and MG type II fibers.
• SF induced atrophy and reduced absolute force (mN) in MG type I fibers.
• Maximal fiber shortening velocity remained unaffected by spaceflight.

Conclusions:

• Spaceflight and ground controls induce muscle atrophy and reduce force and power in slow-twitch soleus fibers.
• Spaceflight exacerbates these effects, particularly on relative force in various fiber types.
• Cellular adaptations in muscle fibers during short-duration spaceflight are significant and fiber-type specific.