Many workouts take people through difficult but safe exercises which first create a burning sensation in muscles, then cause temporary exhaustion. Taking muscles to their performance limits stimulates growth of new muscle tissue and increases physical strength. If a feeling of overall fatigue persists after the workout, you may have skipped some important health maintenance steps in your exercise program. Consult your doctor before beginning any new fitness regimen, and if your exhaustion persists or worsens.
Muscle Exhaustion
Intense exercise burns up stores of glycogen in muscles and uses up oxygen in the blood. When either the fuel or the oxygen depletes faster than the body renews it, muscles fatigue and eventually reach exhaustion --- the inability to perform. Muscles recover quickly in normal circumstances; indeed, researchers tell the "New York Times," periods of exercise actually contribute to a feeling of well-being and energy throughout the day.
Instinctive Cutoff
Many athletes experience a battle of wills between body and mind, fighting exhaustion through willpower. The conscious mind does not make the eventual decision to stop muscle activity, according to research published in 2010 in the journal "Experimental Physiology." Author Markus Amann explains that each individual has an exhaustion point, beyond which some muscle strength remains. During either anaerobic or aerobic workouts, when internal biochemical changes approach this triggering level, the central nervous system stops sending nerve impulses to the muscle. Muscles experience temporary exhaustion in order to prevent damage to tissue.
General Fatigue
When workouts create lingering fatigue or mild exhaustion, your daily routine may be behind these problems. Not eating properly before the workout reduces your capacity to exercise and increases your chances of hypoglycemia, or low blood-sugar levels, the University of Maryland Medical Center reports. Lack of sleep also deprives your body of the time it needs to repair and recover after intense workouts.
Over-Training
Fatigue which causes a steady decrease in performance levels over a period of weeks indicates over-training. Over-training takes two forms, according to the Hospital for Special Surgery: The first, called over-reaching, takes several days of intense workouts to develop. Over-reaching causes severe muscle soreness. Athletes should treat over-reaching with rest, not more exercise. Continuing to work out, meanwhile, causes over-training, marked by an actual drop in ability. Over-training causes many serious physical and mental problems and could require weeks of recovery.
Anemia
Even athletes in the best of health could suffer from iron-deficiency anemia, Vanderbilt University researcher Michelle Baldwin explains. Running on pavement and other hard surfaces ruptures blood cells in the feet, potentially causing an anemic condition called foot-strike hemolysis. The kidneys filter out damaged cells, and overall iron levels drop. Unusually intense workouts also cause blood loss from muscle tissues. Iron supplements can help correct the problem, though you should consult your doctor before taking supplements of any kind.
