You’ve just started a new exercise program in the gym or have taken up running. The following day the muscles you have been exercising are sore, achy and tired. This is Delayed Onset Muscle Soreness. The muscle discomfort and fatigue is commonly blamed on lactic acid build up by many athletes. However this is a fallacy. Lactic acid is not the culprit for this muscle soreness.
Lactic acid is produced during high levels of activity when the oxygen requirements of the muscles are higher than can be supplied by the blood circulation system. In order for the body to produce the required energy, then the body begins another process, anaerobic metabolism, which does not require oxygen.
During the breakdown of glucose and carbohydrates, the cells of the body make ATP (adenosine triphosphate) which provides energy for most chemical reactions in the body. Lactic acid is a by-product of this reaction.
Lactic acid has a bad reputation. When it is made by the body, it splits into lactate ion (lactate) and hydrogen ion. The hydrogen ion (H+ acid) can interfere with electrical signals in the muscles and nerves, slows energy reactions and impairs muscle contractions. The burn felt during intense exercise is considered to be caused by hydrogen ion build-up. Lactate on the other hand is an extremely fast fuel. Whenever carbohydrates are used, a significant proportion is converted to lactate. This lactate is then used in the tissues as fuel or it is transported via the blood stream to other parts of the body that require energy.
Rapid use of carbohydrates for energy production during intense exercise accelerates lactic acid production. Temporarily lactic acid builds up in the muscles and blood, causing the familiar muscle burning sensations. If the intensity of the exercise is reduced then the rate of lactate used for energy soon catches up with the rate of lactate production.
Delayed Onset Muscle Soreness (DOMS)
Lactic acid is responsible for the burning muscles during and after exercise and this is why many suspect it to be responsible for soreness 24-36 hours after intense exercise. However, lactic acid is completely flushed out of muscles within 30-60 minutes of finishing intense exercise. There is no abnormal levels of lactic acid in the tissues or blood when the dreaded DOMS strikes.
Research indicates that DOMS is more likely caused by localised damage to the muscle fibres membranes, the connective tissue and the contractile elements – namely microtrauma to the muscle fibres. Over the 24 hours after intense exercise, the damaged muscles become sore and inflammed. Chemical irritants are released from damaged tissue, triggering pain receptors. In addition to the injured muscle fibres, there is an increase in blood flow causing a swelling of the muscle tissues which again may stimulate pain receptors. In the morning following the exercise, the muscle fibres are fatigued, have microscopic tears and are inflammed. The muscle nerve supply perceives this as an abnormal state and sends pain messages to the pain.
Typical recommendations for dealing with DOMS include light stretching and exercise, massage (of course!), submersion in a hot bath, etc. All these are aimed at lightly increasing blood flow to the muscles and damaged tissues to facilitate repair (and not flushing out non-existing lactic acid buildup).