Delayed onset muscle soreness (often referred to as (DOMS) is bought about by damage to muscle tissue. It is primarily caused by eccentric exercise as is often seen in resistance training, where the muscles are lengthened under tension. During this exercise, the ‘braking’ forces produce small micro tears in the muscle tissue which results in the leakage of calcium and metabolic by-products. This then leads to further injury and inflammation, causing the resultant pain and stiffness that we feel the next day or two (or more!).
The micro tears seen in muscles after exercise promote the activation of ‘satellite cells’. These are cells which are similar to muscle stem cells, that when stimulated fuse to damaged muscle to promote protein synthesis and resultant muscle repair and regeneration. Considering this, muscle soreness can be taken as a sign that the muscles are set to be renewed and are ready to come back stronger than before.
This does not mean however, that if you’re not feeling sore after a strength session then the exercise is not working. The human body is highly adaptive- muscle fibres, connective tissues and the immune system becomes increasingly efficient in dealing with the damage that is associated with exercise. Through regular exercise, various adaptations take place that gradually reduce the sensation of pain. Generally speaking, the more experience that you gain with exercise the more resistant you become to muscle soreness even though you’ve invariably inflicted damage.
It’s important to know that too much muscle soreness is not a good thing. Therefore, when starting an exercise routine start off with a lower volume and intensity and then increase the load as you’re tolerance to the exercise builds and be sure to allow for recovery time between sessions. Following this process reduces the risk of injury through overuse or over-exertion, but still allows you to get the health benefits and adaptations.