Final answer:
EMG biofeedback measures neuromuscular activity and provides feedback to the user, enhancing their ability to control involuntary muscle responses. The correct definition is 'Output increases as the muscle contraction becomes stronger', which indicates that the strength of the biofeedback signal corresponds to the contraction strength.
Step-by-step explanation:
The definition that best represents measuring with EMG biofeedback is 'Output increases as the muscle contraction becomes stronger'. EMG, or electromyography, is a technique used to measure neuromuscular autonomic activity and provide feedback. This feedback can be visual or auditory, indicating the level of muscle activity. The strength of the signal increases proportionally with the intensity of the muscle contraction.
Neuromuscular activity is critical for force production, which is determined by the number of muscle fibers, or myofibers, contracting in response to action potentials from neurons. During a muscle contraction, if more action potentials are sent to the muscle or if more muscle fibers are activated, the force of the contraction will be greater, something that can be monitored with EMG biofeedback. This can help in learning to control involuntary bodily processes, which can be beneficial for treating conditions like tension headaches, high blood pressure, and phobias.
Therefore, biofeedback allows observation of changes in muscle activity in real-time, which can be used to gauge the strength of muscle contractions and help in regulating them. The more intense the contraction, the higher the EMG output.