Test-Heptylate 300 - Rohm Labs

Testosterone heptylate is a long-acting testosterone ester studied for its anabolic effects on muscle. Research shows its limited ability to prevent atrophy caused by hindlimb suspension (HS), a condition simulating muscle disuse. Administered at a dose of 10 mg/kg weekly, testosterone heptylate showed greater influence on fast-twitch muscles like the extensor digitorum longus (EDL) than on slow-twitch muscles such as the soleus (SOL). HS altered muscle fiber composition, reducing type I fibers and increasing type IIa and intermediate fibers in slow-twitch muscles, but testosterone did not reverse these changes. Combined treatment with testosterone and HS resulted in a reduction in steroid receptor sensitivity and binding capacity, further limiting its effects. Mechanical factors like muscle load and receptor sensitivity likely play critical roles in the response to testosterone heptylate. Despite its potential for influencing fast-twitch muscle fibers, its inability to mitigate HS-induced slow-twitch atrophy highlights the complexity of testosterone's effects.