Muscle Fatigue: Why Do Muscles Shake When Lifting?

Muscle trembling during weightlifting or intense exercise is a result of muscle fatigue. Muscle fatigue, in simple words, refers to the state when our muscles get tired. To understand this phenomenon, it is better to first understand what happens to our muscles when we exercise or lift weights. The signal for the muscle to move comes from the spinal cord, through the neurons, and down to our muscles. Each neuron connects to a number of muscle cells rather than a single muscle cell. The neuron, along with the muscle cells to which it is connected, is known as a motor unit.

When muscular fatigue occurs, some of the motor units stop functioning for a time. The pressure is then put on the working units. As the remaining motor units begin to work in tandem, they give rise to sudden jerky movements, which we feel as trembling.