“No pain, no gain”, right? Well, not exactly. It is important to understand the differences in discomfort caused by exercise. It is never a good thing to experience a sharp pain during exercise because that is a sure sign that something is wrong especially if it occurs in or near a joint. But what is that burning sensation that prevents you from pushing through more repetitions? And why do you sometimes hurt a day or two after exercise but felt fine while you were working out?

The burn you feel is caused by a build up of lactic acid in the muscles. Muscle contractions require oxygen and when the contractions are slow and regular, the body is able to produce a substance called pyruvate which is then broken down to produce more energy. When demands exceed the body’s ability to supply the muscle with oxygen, the pyruvate is converted to lactase which allows glucose or glycogen to breakdown for more energy. Lactase is acidic and builds until the muscle is able to recover and once again utilize oxygen. That is why after a short period of rest, you are able to continue until the muscles fail again.

The aches and stiffness you feel a few days after vigorous exercise are a different story. Delayed Onset Muscle Soreness is due to the micro-tears that occur within the muscle after strenuous exercise. In your body’s effort to heal these tears, inflammation occurs which causes the soreness. The micro-tears are more apt to occur when doing eccentric (lengthening) exercises. Muscles elongate under tension when the opposing force is greater than the force generated by the muscle. Examples would be the “negative” contraction during weight-lifting or running downhill. Rest is needed for the muscle soreness to go away and although it feels good to stretch, it really has no bearing on how quickly the soreness will dissipate.

It is important to distinguish between soreness and pain. Acidosis will burn and require you to temporarily rest, DOMS will make you stiff and sore and require 2 or 3 days of rest, and pain will more than likely keep you out of the gym and require total rest or medical intervention.