Passive stretch acutely activates anabolic intracellular signaling pathways, including mTORC1 and MAPK, which regulate muscle protein synthesis and hypertrophy, as consistently demonstrated in rodent and in vitro muscle cell models. These mechanosensitive pathways convert mechanical tension into chemical signals that promote muscle growth, providing a biological foundation for stretch-based hypertrophy interventions.

Holding a stretch for a long time might build muscle and strength in your calves by triggering the same biological signals that weightlifting does. Researchers think this happens because the stretch creates tension that activates growth pathways in your muscles, though we haven't directly proven this in humans yet.

When your muscles swell up from the burn during a workout, that puffiness might trick your cells into thinking they’re being stretched, turning on growth signals — like a fake workout signal.

When you lift weights, the pulling force on your muscles is what makes them grow bigger—not hormones or feeling tired. This force turns on internal signals that tell your muscles to make more protein and get larger over time.

When your muscles swell up from fluid buildup during a tough workout, that pressure might send signals to your cells to grow bigger — even if you’re not lifting heavy weights.

When your muscles contract or get stretched, the physical pull they feel is the main reason they grow bigger — it's like the muscle gets a signal from the tugging to grow more muscle fibers.