What electrical changes occur in muscles as they get tired? student subjects are instructed to hold their arms above their shoulders as long as they can. Meanwhile, the electical activity in their arm muscles is measured. This is

a common method used to study muscle fatigue.

When muscles get tired, several electrical changes occur in the muscle tissues. One of the primary changes is an increase in the activity of motor units, which are made up of a motor neuron and the muscle fibers it innervates. As the muscle fatigues, the motor units are recruited more frequently to maintain the force production.

Electromyography (EMG) is a technique used to measure the electrical activity in the muscles. It involves placing electrodes on the surface of the skin overlying the muscles of interest. These electrodes detect the electrical signals generated by the muscle fibers during their contraction.

During the task of holding the arms above the shoulders, as the muscles get tired, there are a few key electrical changes that can be observed through the EMG measurements. These changes include:

1. Increased amplitude: As the muscle fatigues, the amplitude or strength of the electrical signals measured by the electrodes tends to increase. This indicates the increased recruitment and firing frequency of motor units to generate the necessary force to sustain the position.

2. Decreased frequency: The frequency of the electrical signals, usually represented by the number of times the muscle fibers fire per second (Hertz), tends to decrease as fatigue sets in. This decrease in firing rate can be attributed to the decreased ability of the muscle to sustain high-frequency contractions.

3. Recruitment of additional motor units: As the muscles tire, additional motor units that were initially not active or minimally active during the task are recruited. This recruitment helps compensate for the fatigue in the already active motor units and allows for the maintenance of muscle force.

These electrical changes, observed through EMG measurements, provide valuable insights into the neuromuscular mechanisms associated with muscle fatigue. By studying these changes, researchers and scientists can understand how muscle fatigue occurs, how it affects performance, and design strategies to delay or prevent the onset of fatigue.