Effect Of Fortetropin? Ingestion On Muscle Size And Circulating Myostatin During Disuse Atrophy

Fortetropin® (FOR), from fertilized egg yolks, supplementation has been shown to reduce circulating myostatin, which may affect muscle growth. In addition, FOR ingestion prevented disuse-induced muscle atrophy in canines. However, the effect of FOR supplementation on human skeletal muscle adaptation during muscle disuse is unknown. PURPOSE: To determine the effect of FOR supplementation on muscle size, strength, and circulating myostatin in young men during 2-wk of single-leg immobilization and recovery. METHODS: 24 healthy young men (22 ± 2 yrs) were randomly allocated to either FOR supplement (FOR-SUPP, n = 12) group consuming 19.8 g/d of FOR or placebo (PLA-SUPP, n = 12) group for 6-wk (2-wk run-in, 2-wk single-leg immobilization, and 2-wk recovery). Participants wore a knee brace on a randomly selected leg during the immobilization phase. Blood samples were collected at days 1 and 42 to measure plasma myostatin. Dual-energy X-ray absorptiometry, ultrasonography, muscle biopsies, and isometric knee-extensor torque test were performed prior to and following each phase (days 1, 14, 28, and 42) to measure immobilized-leg lean mass (LM), vastus lateralis cross-sectional area (CSA), the percentage of myostatin-positive satellite cell (MSTN+/PAX7+), and muscular strength. RESULTS: Circulating myostatin was increased on day 42 compared to day 1 in PLA-SUPP (4221 ± 541 pg/mL to 6721 ± 864 pg/mL, P < 0.05) but not in FOR-SUPP (5487 ± 489 pg/mL to 5382 ± 781 pg/mL, P > 0.05). vastus lateralis CSA declined from 28 ± 1 cm2 on day 1 to 26 ± 1 cm2 after the immobilization phase (day 28) (P < 0.05), and immobilized-leg LM decreased from 10.8 ± 1.4 kg on day 1 to 10.6 ± 1.4 kg at day 28 (P < 0.05), with no difference between groups. MSTN+/PAX7+ satellite cells associated with type II fibers increased from 35 ± 5% on day 1 to 55 ± 5 % on day 28 (P < 0.05), and isometric strength decreased from 160 ± 10 Nm on day 1 to 129 ± 9 Nm on day 28 (P < 0.001), with no difference between groups. The increased MSTN+/PAX7+ and decreased isometric strength were not different from pre-immobilization after 2 weeks of recovery. Neither vastus lateralis CSA nor immobilized-leg LM recovered (no difference between groups). CONCLUSIONS: FOR ingestion prevented the rise in circulating myostatin but not disuse-induced muscle atrophy in young men.