Introduction
disuse-induced declines, ®
CATABOLIC STATE
Skeletal muscle is a plastic tissue that adapts its structure and metabolism in response to several internal and external variables, particularly mechanical load and protein ingestion [Myostatin (or growth differentiation factor-8, GDF-8) is a negative regulator of muscle growth and a member of the transforming growth factor-β family [A previous study reported that 12-wk of Fortetropin® (FOR) ingestion, a non-thermal pasteurized, freeze-dried high protein egg yolk product, with resistance training lowered serum myostatin by 18–22% and increased muscle thickness by 3.7% and lean mass (LM) by 3.3% in trained young men, but placebo did not [The primary aims of this trial were to determine whether FOR supplementation could prevent disuse-induced declines in muscle cross-sectional area (CSA) measured by ultrasonography and muscle biopsy (muscle fiber CSA), LM using dual-energy X-ray absorptiometry (DXA), and isometric strength during two weeks of single-leg immobilization phase. We hypothesized that FOR supplement would attenuate the decline in muscle size during immobilization, which would coincide with a reduction of circulating myostatin and alterations of molecular markers favoring a less catabolic state.