DOMS is frequently experienced when you exercise at a level the body is not used to working at. This means that athletes who have upped the intensity of their training can have DOMS just as much as complete beginners who are trying to improve their fitness and strength.
But what is it?
Well, truth be told, the science world does not have a definitive definition of what is happening when the body experiences DOMS! Typically, it has been described as the inflammatory response to small tears in the muscle; micro trauma of muscle tissues; and/or a reaction to the build-up of lactic acid. All of these have been investigated but the evidence to support them is weak.
What we do know is that DOMS is muscular pain that can be over a wider area than just the muscle activated. Usually it is the action of eccentric exercises (for example, if you are lifting a heavy weight in your arms you might contract a muscle to lift up the load but you eccentrically exercise the muscle as you go to lower the weight back down) that causes DOMS to be felt. Typically, the pain is felt 24 to 72 hours after the offending activity! However, it can take as long as a week to resolve. We also know that during this period the muscle has less strength and stamina than prior to the exercise.
Ultrasound scans of muscles experiencing DOMS shows increased oedema (swelling) within the muscle fibres. There is strong support that this swelling is an inflammatory response to the trauma incurred during the exercise but it doesn’t explain the more widespread pain.
Recently, there is emerging evidence that chemicals that initiate nerve growth contribute to increased sensitivity to muscular pain when they are damaged. This substance is referred to as Nerve Growth Factor (NGF). It is the nervous system that causes muscles to contract as the nerves attach to various parts of the muscle cell at neuromuscular junctions. In addition, there are nerves that provide sensory information such as heat and pressure.
What if eccentric exercise damages the nerve endings as well as the muscle fibres? This would then release NGF into inflamed muscular tissue possibly causing additional reactions to occur.
We know that the body’s normal inflammatory response takes about 24 hours to kick in (which is why anti-inflammatories are discouraged at time of injury). DOMS also takes some time to exert its effect. So as the inflammation reaches its peak there appears to be a slight timelag before DOMS is fully experienced. At the injury site the body is sending a constant flow of inflammatory response cells to the area to repair the injured site leading to increased oedema but material is also being taken away.
Could the oedema then dissipate through lymphatic channels and along fascial lines (fascia is a type of connective tissue that among other things wraps around muscle and individual muscle fibres)? This would then explain why DOMS is felt over a wider area than just the injured muscle.
But why would the body produce a response that inhibited our strength and movement albeit for a short time?
Well, in our muscles there are various types of receptors, including a type called mechanoreceptors. These receptors respond to mechanical pressure or distortion. There is evidence that NGF helps to improve the threshold that these mechanoreceptors work: effectively increasing the resilience of these receptors.
We also know that as we repeat an exercise we get better at it and can increase the intensity of the workout. Thus making the muscles being worked stronger. This would make sense in evolutionary terms and survival of the fittest approach. It would also help to explain why, when we do a different exercise using the same muscles we can still get DOMS: because the mechanical pressure and distortion of the fibres is different.
This is interesting stuff! Although still unproven.
So, although we still don’t know what DOMS is, there are some new insights into our understanding of what it is! However, it is a good sensation to experience, just be careful, for your own comfort!