muscle weakness

Muscle weakness occurs when a muscle fails to develop expected force. This can stem from issues in the nerve impulse pathway, from the brain to the muscle, or from defects within the muscle itself.12

The process begins with a nerve impulse traveling from the brain to the spinal cord, then to the neuromuscular junction. Here, a chemical messenger called acetylcholine is released, which triggers muscle fiber contraction. If any part of this chain is disrupted, muscle weakness can result.13

Neuromuscular junction disorders, such as myasthenia gravis, can cause weakness and fatigue, especially with exercise. Weakness can lead to difficulties with everyday activities, like dropping objects or experiencing "foot drop," and can be assessed through physical examination, force measurement, and sometimes muscle biopsies.124