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Principal Investigators: Attie, K. M., Borgstein, N. G., Lau, H., Rosenberg, E., et al. (Acceleron Pharma, Cambridge, Massachusetts)
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Methodology: A randomized, double-blind, placebo-controlled human study enrolling 48 healthy postmenopausal female volunteers. Participants were randomized into cohorts receiving a single subcutaneous injection of either a placebo or varying dose gradients of ACE-031 ($0.02\text{ mg/kg}$ up to $3\text{ mg/kg}$). Changes in skeletal muscle mass volume were precisely tracked via dual-energy X-ray absorptiometry (DEXA) and high-resolution magnetic resonance imaging (MRI) of the thighs.
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Key Findings: A single $3\text{ mg/kg}$ dose of ACE-031 produced rapid and unprecedented physical changes. Within just 29 days post-injection, human subjects achieved a statistically significant mean increase of $3.3\%$ in total lean body mass (equivalent to roughly $1\text{ kg}$ of pure muscle tissue) and a concurrent $5.1\%$ increase in thigh muscle volume measured via MRI. The trial provided definitive human proof that sequestering myostatin with decoy receptor configurations triggers immediate, highly efficient muscle hypertrophy.
