Muscle volume, MRI relaxation times (T2), and body composition after spaceflight

TLDR

Muscle volume, calf muscle T2, and body composition were measured in 4 crewmembers after a 17‑day mission and in 14–16 crewmembers on 16‑ to 28‑week shuttle/Mir missions. Seventeen‑day missions caused 3–10% loss in most muscle regions (hamstrings spared), while 16‑ to 28‑week missions produced 5–17% volume loss in all groups except neck; these changes plateaued by 4 months, reversed within 30–60 days, and were accompanied by postflight swelling and elevated calf T2 suggesting damage, with 17‑day flights also losing fat but not lean mass, whereas longer missions lost lean mass and bone mineral (~3.4–3.5%) but not fat, and the pelvis showed the greatest bone loss (13 %).

Abstract

Postflight changes in muscle volume, calf muscle transverse relaxation time, and total body composition were measured in 4 crewmembers after a 17-day mission and in 14–16 crewmembers in multiple shuttle/Mir missions of 16- to 28-wk duration. During the 17-day mission, all muscle regions except the hamstrings significantly decreased 3–10% compared with baseline. During the shuttle/Mir missions, there were significant decreases in muscle volume (5–17%) in all muscle groups except the neck. These changes, which reached a new steady state by 4 mo of flight or less, were reversed within 30–60 days after landing. Postflight swelling and elevation of calf muscle transverse relaxation time persisted for several weeks after flight, which suggests possible muscle damage. In contrast to the 17-day flight, in which loss in fat, but not lean body mass, was found (25), losses in bone mineral content and lean body mass, but not fat, were seen after the longer shuttle/Mir missions. The percent losses in total body lean body mass and bone mineral content were similar at ∼3.4–3.5%, whereas the pelvis demonstrated the largest regional bone loss at 13%.