You’re working out. The first time you do it, it sounds easy, but each succeeding attempt has become increasingly difficult. Within the arms, the muscles that help with lifting have atrophied. But never give up! Muscles that are tested by larger tasks end up doing better for your body.
What causes our muscles to become tired? Lactic acid or a lack of energy are often blamed, but these causes alone do not account for muscle exhaustion. Another essential aspect is the capacity of the muscle to respond to brain signals.
It helps to understand how a muscle contracts in response to a nerve signal in order to understand the causes of muscle fatigue. Motor neurons are long, thin cells that transmit signals from the brain to the muscles in a fraction of a second.
A tiny distance divides the motor neuron and the muscle cell, and the exchange of particles through this gap causes the muscle cell to contract. The motor neuron produces the neurotransmitter acetylcholine on one side of the gap.
Charged particles, or ions, line the muscle cell membrane on the other side: potassium on the inside and sodium on the outside. The motor neuron releases acetylcholine in response to a signal from the brain, which allows pores on the muscle cell membrane to open.
Sodium enters and potassium leaves the body. The flux of these charged particles is an important step in muscle contraction: the charge shift produces an electrical signal known as an action potential, which passes through the muscle cell and induces the release of calcium that has been stored within it.
The muscle contracts as a result of the calcium flood because proteins buried in the muscle fibers lock together and ratchet towards each other, pulling the muscle close. A molecule called ATP provides the energy to power the contraction.
After that, ATP assists in pumping the ions back through the membrane, resetting the sodium and potassium balance on either side. Any time a muscle contracts, the entire process is repeated. With each contraction, ATP is depleted, waste products such as lactic acid are formed, and some ions drift away from the cell membrane of the muscle, leaving a smaller and smaller group behind.
Despite the fact that muscle cells use up ATP as they contract regularly, they are continually producing more, so even highly fatigued muscles have not lost this energy source. And, despite the fact that many waste products are acidic, fatigued muscles retain a pH within normal ranges, suggesting that the tissue is clearing these wastes effectively.
However, after a number of contractions, there may not be enough potassium, sodium, or calcium ions near the muscle cell membrane to properly reset the process.
Even if the brain sends a signal, the muscle cell is unable to produce the requisite action potential to contract. And when ions such as sodium, potassium, or calcium are depleted in or near the muscle cell, they are abundant elsewhere in the body.
They will flow back to the places where they are needed with a little time, often with the aid of active sodium and potassium pumps. Muscle exhaustion will be relieved if you take a break and relax, as these ions will be replenished in the muscle.
Since fewer cycles mean slower ion depletion, you can exercise for longer at the same intensity as your physical health increases. Many muscles expand as a result of exercise, and larger muscles have more ATP stores and a greater capacity to clear waste, delaying exhaustion even longer.
Source : Youtube
