The theory you’re referring to posits that performing one-rep max (1RM) lifts—essentially lifting the heaviest possible weight for a single repetition—can promote muscle hypertrophy (growth) primarily through acute hormonal responses. In essence, the intense stress of a max effort lift is thought to trigger a surge in anabolic hormones like testosterone, growth hormone (GH), and insulin-like growth factor-1 (IGF-1), which then enhance protein synthesis, muscle repair, and overall growth. This idea stems from observations that heavy lifting elicits these hormonal elevations, potentially creating a more favorable environment for hypertrophy beyond just mechanical tension on the muscles.

Proponents argue that these hormonal shifts act systemically: for example, testosterone binds to androgen receptors in muscle fibers to boost protein synthesis via pathways like PI3K/Akt/mTOR, while GH stimulates IGF-1 production from the liver, further amplifying those signals. 3 Heavy low-rep training (e.g., singles, doubles, or triples) is also said to recruit high-threshold motor units more effectively, leading to neural adaptations and hormone release that support growth. 6 Some sources highlight that weightlifting in general triggers testosterone and GH release, aiding tissue repair and regeneration. 8 10

However, the evidence is mixed and often doesn’t strongly support this as the primary mechanism. Multiple studies on trained individuals show that load (heavy vs. moderate/light) doesn’t dictate hypertrophy when sets are taken to volitional failure—gains in muscle size are similar across rep ranges, suggesting mechanical tension and metabolic stress play larger roles than hormones. 0 2 13 Acute post-exercise hormonal spikes are often unrelated to long-term strength or muscle gains; they’re transient (peaking shortly after training and dropping quickly) and don’t correlate with hypertrophy outcomes. 0 14 The “repetition continuum” model traditionally links heavy loads (1-5 reps) more to strength gains than hypertrophy, with moderate reps (6-12) better for muscle growth, and hormonal rationale for the latter has been called dubious. 2

In practice, 1RM lifting is great for building maximal strength and neural efficiency, but for hypertrophy, it’s often combined with higher-volume work. If hormonal shifts do contribute, they’re likely secondary to factors like total training volume and progressive overload. Always warm up thoroughly and use spotters for safety with max attempts.