There are more reasons that can lead to leg weakness and fatigue. Exertion can lead to physiological fatigue. Diabetes mellitus, hypothyroidism, hypokalemia, diarrhea and dehydration, cardiac insufficiency, cold and fever can all lead to pathological weakness. In diabetes mellitus, the body’s impaired utilization of glucose affects the energy supply to the leg muscles, inducing weakness and fatigue. In hypothyroidism, metabolic activity is reduced and the leg muscles cannot effectively utilize glucose and fat for energy, inducing weakness and tenderness. Electrolyte disturbances due to dehydration from diarrhea, and hypokalemia induced by the transfer of potassium ions into the cells during periodic paralysis, affect the electrical activity of the muscles and weakness occurs. The decreased pumping function of the heart in cardiac insufficiency will result in insufficient blood supply to the muscles, inducing symptoms such as weakness and leg weakness. When you have a cold or fever, you are prone to symptoms such as limb weakness and fatigue due to energy depletion and the effect of toxins produced by viruses.