Science shows mechanical tension, not microtears, is main driver of muscle growth

Current evidence in exercise science suggests that mechanical tension, rather than the old “tear and repair” idea, is the primary driver of muscle hypertrophy, says Dr Anne Brady, a kinesiology professor who specialises in muscle quality, physical function and body composition. When a lift is heavy enough or repetitions reach near-failure, the resulting tension stretches the membrane around muscle cells.

Mechanoreceptors detect that stretch and activate the mTOR pathway, which signals muscle protein synthesis. Brady says muscle damage “certainly contributes, but it’s not the main factor” and that metabolic stress — the familiar “burn” — acts as an amplifier to mechanical tension. There are two main types of hypertrophy: myofibrillar, which increases contractile filaments and strength, and sarcoplasmic, which expands fluid volume and increases size without the same strength gains.

A 2019 study cited in the piece found high-volume training produced mainly sarcoplasmic gains in young men; the most effective growth appears when high tension is combined with enough repetitions to create metabolic stress. The practical implications are that soreness is not a reliable marker of effectiveness and excessive damage can hamper progress by reducing training frequency.

Key Topics

Health, Muscle Hypertrophy, Mechanical Tension, Dr Anne Brady, Mtor Pathway, Myofibrillar Hypertrophy