The main reason muscles grow bigger when you work them is because of the force they create when they squeeze — and right now, science says that’s the only proven main trigger.

Your muscles grow bigger mainly because of how much total force they feel over time—not whether you do your workouts all at once or spread out over the week.

Your muscles grow bigger mainly because of how much total force they feel over time—not whether you do your workouts all at once or spread out over the week.

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.

You can grow muscle not just by lifting weights, but also by stretching—just as long as the muscle feels enough tension, no matter how it's created.

When you move your muscles through their full stretch and contraction during exercise—like fully lowering and raising a dumbbell—you build more muscle than if you only move partway, because the muscle gets stretched under load, which seems to trigger better growth.