Protein supplementation increases postexercise plasma myostatin concentration after 8 weeks of resistance training in young physically active subjects.

Myostatin (MSTN) is a negative regulator of muscle growth even if some studies have shown a counterintuitive positive correlation between MSTN and muscle mass (MM). Our aim was to investigate the influence of 2 months of resistance training (RT) and diets with different protein contents on plasma MSTN, interleukin 1 beta (IL-1β), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), and insulin-like growth factor 1 (IGF-1). Eighteen healthy volunteers were randomly divided in two groups: high protein (HP) and normal protein (NP) groups. Different protein diet contents were 1.8 and 0.85 g of protein·kg bw(-1)·day(-1) for HP and NP, respectively. Subjects underwent 8 weeks of standardized progressive RT. MSTN, IGF-1, IL-1β, IL-6, and TNF-α were analyzed before and after the first and the last training sessions. Lean body mass, MM, upper-limb muscle area, and strength were measured. Plasma MSTN showed a significant increase (P<.001) after the last training in the HP group compared with NP group and with starting value. IGF-1 plasma concentration showed a positive correlation with MSTN in HP after the last training (r(2)=0.6456; P=.0295). No significant differences were found between NP and HP for IL-1β, IL-6, TNF-α, and strength and MM or area. These findings suggest a "paradoxical" postexercise increase of plasma MSTN after 8 weeks of RT and HP diets. This MSTN elevation correlates positively with IGF-1 plasma level. This double increase of opposite (catabolic/anabolic) mediators could explain the substantial overlapping of MM increases in the two groups.