How TRAINING promotes muscle growth

The three stimuli of muscle hypertrophy all work quite differently. The primary driver is mechanical tension, with metabolic stress and muscle damage working on a less direct basis (see Stimuli Of Growth).

Mechanical tension

For muscle hypertrophy to occur, there must be a mechanical stimulus (or stress). This mechanical stimulus is referred to as mechanical tension or muscular tension. When you contract your muscles against resistance, you create mechanical tension via the force placed on your muscles. Once mechanoreceptors within the muscle detect such tension, a cascade of chemical reactions leading to muscle growth begins.

from work to growth

The physical stimulus of resistance work on mechanical tension, in turn, stimulates a range of chemical and biological responses that result in bigger and stronger muscles.

DK

n Double-tap image to read the labels

forces within muscles

Both longitudinal and lateral forces generated by muscle contractions are ultimately transmitted to bones and tendons to generate movement.

DK

n Double-tap image to read the labels

Forces at the microscopic level

During strength training, forces are transmitted longitudinally from one sarcomere to the next along the length of a muscle fiber and laterally via the costameres (linking the fiber to the sarcolemma) and the collagen wrapping around them, the endomysium.

The myotendinous junction

Muscles connect to bones via tendons. Where the tendon meets the muscle is known as the myotendinous junction. This area is a common site of injury.

DK The creation of tension in muscles

When actively contracting, muscles can generate mechanical, or muscular, tension while shortening, lengthening, or staying the same length. The tension depends on how big or small the overlap is between the actin and the myosin myofilaments within a sarcomere (see The Cycle Of Contraction).

DK

n Double-tap image to read the labels

Feedback to the brain

Muscle spindles (within skeletal muscle) are mechanoreceptors sensitive to the magnitude and duration of loading by detecting changes in the length of a muscle. Proprioceptors (located within joints, muscles, and tendons) are sensitive to tension and pressure. These provide the brain with information about the body’s posture and position of its parts.

DK

n Double-tap image to read the labels

Metabolic stress

This secondary driver of muscle hypertrophy is an exercise-induced accumulation of metabolites—the intermediate products of metabolic reactions catalyzed by enzymes within a cell; common metabolites are lactate, inorganic phosphate, and hydrogen. Low blood oxygen (hypoxia) can also promote the release of hormones and cytokines (signaling proteins) during contraction. The main theory explains that as muscular fatigue and metabolites build, it leads to higher levels of tension in fast-twitch fibers, stimulating them to grow.

Another by-product of metabolic stress that is thought to contribute to the amount of mechanical tension during muscle contraction is cell swelling (also called “the muscle pump”). Raised internal pressure within the muscle leads to more tension being produced—boosting the total amount of mechanical tension during contraction.

DK

n Double-tap image to read the labels

muscle damage

This contributor to muscle growth is specifically exercise-induced muscle damage. It exists on a continuum spanning from mild damage, which can be potentially helpful toward muscle growth, to severe damage, which can cause great disruption of tissues and negative effects across the body.

More damage is not better

A common mistake is that more exercise-induced muscle damage (and soreness) is better. Although muscle soreness is a sign you placed tension in the target muscles, large amounts of muscle damage limit your ability to improve over time. It was once thought that muscle damage was a positive because it impacts on building new muscle. But it’s now known that the higher levels of muscle protein synthesis seen are mainly helping rebuild and repair the muscle after the damage of an intense training session rather than adding new contractile proteins.

hamstring ball curl

Within one exercise, different muscles are contracting isometrically, concentrically, and eccentrically. Controlling eccentric contractions is crucial to minimizing mechanistic damage to muscle cells.

DK

n Double-tap image to read the labels

Isometric contractions

Muscles creating tension while staying the same length, such as the abdominals, are orange

Concentric contractions

Muscles creating tension while shortening, such as the glutes and quads, are red

Eccentric contractions

Muscles creating tension while lengthening, such as hamstrings and calf muscles, are purple

DK Damaging eccentric contractions

Muscle damage is caused most often with high training volumes and more exaggerated eccentric contractions, which can cause more mechanistic damages to a muscle cell compared to concentric or isometric contractions. The damage caused by eccentric contractions is due to the mechanical disruption of actin–myosin bonds rather than the ATP-dependent detachment. During intense eccentric actions, sarcomeres are being stretched so much that they start to “pop”—think of the folds in the bendy section of a straw—one after the other along the muscle fiber length. The filaments fit back together afterward, but it results in muscle soreness.

DK

n Double-tap image to read the labels

A POPPED SARCOMERE

Recovery is vital to build muscle

The short period of muscle damage due to the intensity of a workout is followed by a longer recovery time, which is key for rebuilding damaged muscle fibers. If you train without enough chance for muscles to recover between sessions, you’ll miss out on the opportunity to rebuild muscle, which will detrimentally affect your performance (see training too infrequently).

DK

n Double-tap image to read the labels

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset
44.220.89.57