Running is an exercise that conditions overall and requires coordination of muscles throughout the body. Some runners notice a burning sensation in the legs during or after running, especially in the thighs. The feeling of burning results from the direct effects of running on the muscle fibers and from a process called lactic acidosis, which can result from heavy oxygen consumption during physically demanding activity.
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The thighs are the hardest working of the muscles used while running. Many muscles work together to shape and form the thigh, including the rectus femoris muscle, the sartotious muscle, the vastus medialis muscle, the vastus lateralis muscle, the adductor longus muscle, the gracilis muscle, the pectineus muscle, the illiopsoas muscle, the tensor fasciae latae muscle and the biceps femoris muscle. Any combination of these muscles can be affected by burning while running.
The burning and soreness in the thighs that accompany running may be associated with microscopic muscle tearing and breakdown from muscle tissue damage on a molecular level. Muscle tissue injury from running is generally a slight tearing and stretching of the muscles and usually heals within a few days. This rarely causes any harm and, in fact, may stimulate muscle growth, conditioning an individual to accommodate running more effectively.
Lactic acidosis may be a cause of the burning pain that sometimes accompanies heavy exercise, says the "American Journal of Physiology." Running is an aerobic exercise, which means it requires a generous supply of oxygen. The body uses oxygen and nutrients as sources of energy while running. When the oxygen consumption is very high, the body begins to use anaerobic metabolism, which does not require oxygen, to produce energy. The byproduct of anaerobic metabolism is a chemical called lactic acid, which is acidic, meaning it has a low pH. Most human tissue, including muscles, sense an irritation and burning when exposed to acidic materials such as lactic acid. This is not dangerous or abrasive, but it can cause burning of the thighs while running.
Conditioning to Reduce Burn
Conditioning can have an impact on the development of lactic acidosis and muscle tearing while running. When muscles are trained for distance or sprint running, their capacity to endure stretching and to maintain energy requirements without switching to anaerobic energy production improves; therefore, the burning from lactic acidosis and muscle tearing and stretching are less likely to occur.
Nutrition for Reduced Burn
Dehydration can contribute to the muscle damage that causes burning while running. Some nutrients ingested before running may minimize the effects of acidosis by counteracting the acidic pH of lactic acid, according to a 2011"Sports Medicine" analysis. Proper hydration and well-tailored nutrition may prevent some development of burning sensation of the thighs while running.