MECHANICAL TENSION - DRIVER OF HYPERTROPHY

MECHANICAL TENSION - DRIVER OF HYPERTROPHY

Before we start, here is a few terms worth while knowing:

-       Motor unit: a motor neuron and all of its associated muscle fibres

-       Motor unit recruitment: different motor units are activated to produce a given level and type of muscle contraction

-       Metabolite accumulation: A substance made or used when the body breaks down food, drugs or chemicals, or its own tissue.

-       Calcium ion-related fatigue: Increased concentration of calcium ions within the cytoplasm, resulting in a reduction in force.

Mechanical tension is known to be the main stimulus for hypertrophy and perhaps the only stimulus. Stretching denervated muscle fibres cause them to grow. Hypertrophy can occur with mechanical tension alone, so without any motor unit recruitment leading to muscle fibre activation, metabolite accumulation , or calcium ion accumulation leading to muscle damage.

PMID: 4270324

PMID: 30565562

An increase in muscular tension (force) with training provides the primary stimulus to initiate the process of skeletal muscle growth or hypertrophy. Changes in muscle size become detectable after only 3 weeks of training, and the remodelling of muscle architecture precedes gains in muscle cross-sectional area. There are fundamental adaptations necessary for muscle hypertrophy (increased protein synthesis and satellite cell proliferation) are mobilised during the initial phases of resistance training. Mechanical stress on components of the muscular system triggers signalling proteins to activate genes that translate messenger RNA and stimulate muscle protein synthesis (MPS) in excess of protein breakdown (remember, your muscle is continuously breaking down unless you give an anabolic stimulus or reduce the rate of breakdown by having a full complimentary protein-based meal with preferably 3g of leucine). Accelerated protein synthesis, specifically when combined with the effects of insulin and adequate amino acid availability, increases muscle size during resistance training.

When does hypertrophy not occur but “feels like it should”?

High levels of motor unit recruitment leading to high levels of muscle activation can occur without hypertrophy being stimulated e.g. fast movements like jumping. You need high levels of muscle activation to occur at the same time as high levels of mechanical tension in order for hypertrophy to occur.

PMID: 9763647

PMID: 20139780

High levels of metabolite accumulation can be present without hypertrophy being stimulated (e.g. during blood flow restriction at rest, without muscular contractions). Only when metabolite accumulation occurs at the same time as high levels of mechanical tension does hypertrophy occur.

PMID: 9763647

PMID: 35622106

Muscle damage can occur without hypertrophy being stimulated, so no, muscle damage is not a stimulus for hypertrophy as popular mainstream media believes. Only when muscle damage occurs after muscular contractions that involve high levels of mechanical tension does hypertrophy occur. The idea that muscle damage is the driver for hypertrophy can be immediately debunked by the fact that concentric-only strength training and isometric training at short muscle lengths produce little or no damage at low-to-moderate volume, yet still produce plenty growth.

PMID: 11668355