Mechanical tension is the primary stimulus for skeletal muscle hypertrophy, with mTORC1 activation via filamin-C-BAG3 signaling identified as a leading candidate pathway, while muscle damage and metabolite accumulation are not essential and lack conclusive evidence to serve as primary drivers of hypertrophy.

Study: The cochaperone BAG3 coordinates protein synthesis and autophagy under mechanical strain through spatial regulation of mTORC1.

When muscles are stretched or worked out, a protein called BAG3 helps turn on muscle growth by activating a key growth switch (mTORC1) in the right place, without needing muscle damage or burn to make it happen.

Study: Load-induced human skeletal muscle hypertrophy: Mechanisms, myths, and misconceptions

This study says lifting weights (mechanical tension) is the main reason muscles grow, and things like muscle burn or swelling aren’t really what cause growth — which matches the claim. It doesn’t talk about the exact molecular switch, but it backs up the big idea.

Study: Mechanisms of mechanical overload-induced skeletal muscle hypertrophy: current understanding and future directions.

This study says lifting weights (mechanical tension) is the main reason muscles grow, and it points to a specific molecular pathway (mTORC1) as the key signal — not muscle tears or burn from exercise. That matches what the claim says.