Mixed
Mechanical load is the primary initiating stimulus for skeletal muscle hypertrophy following resistance exercise, with loads as low as 30% of 1RM being sufficient to trigger near-maximal hypertrophic gains when taken to failure.
To maximize muscle growth, you do not need to lift extremely heavy weights. Research indicates that using loads as low as 30% of your one-repetition maximum can produce near-maximal hypertrophy, provided you train close to muscular failure. Focus on consistent mechanical tension and volume rather than just maximizing the weight on the bar. This approach may reduce injury risk while still effectively stimulating muscle growth.
Mechanical signals are arguably the most intuitive hypertrophy stimuli... a large amount of mainly indirect evidence suggests that mechanical load is a key hypertrophy stimulus associated with resistance exercise. However, the actual loads do not need to be excessive as loads of ~30% of 1RM seem sufficient to trigger near maximal hypertrophic gains.
Why this rating
The paper is a review synthesizing extensive experimental evidence, including human trials and animal models, though it acknowledges some mechanisms are incompletely characterized.
Source
Stimuli and sensors that initiate skeletal muscle hypertrophy following resistance exercise
Henning Wackerhage et al. · Journal of Applied Physiology · 2018
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