As the name suggests, this is a muscular soreness that occurs after a specific event. That event in our case is likely to be a bout of exercise. But physiologically, what’s going on in the muscle, why does it happen and why doesn’t it happen to us every time we train?
Let’s start off with some basic muscle physiology. If we were to look at skeletal muscle under a microscope (as opposed to cardiac or smooth muscle, which aren’t involved in moving our bodies), we would see a chequerboard of cells nicely, neatly arranged. When we move, those cells contract or squeeze together – think about when you flex your biceps muscle. You can see it getting shorter when it contracts – that is the result of those cells contracting. After a period of exercise, that neat, ordered microscope image would look quite different. Now we would see a much messier pattern as the cells have become disrupted and damaged. Here, damaged is the correct word but may sound more serious than we need it to – every time we exercise, ideally we are looking for progressive overload. That is to say that what we’re asking our body to do is ever so slightly beyond our current ability. If we don’t do that when we train, then our body has no reason to adapt and become stronger (in the case of weight training). That’s not to say that every session needs to get harder and harder – rest is still important, and we need to periodise our work on a session-by-session, week-by-week and month-by-month basis.
But back to the microscope. So, after our session we would see that damage, or micro-trauma, as it’s known. And it’s a good thing – it’s bringing da gainz! These micro-traumas aren’t solely responsible for DOMS though – in fact you can have DOMS with no trauma, but generally they do factor into the explanation.
As well as the trauma, another factor that can lead to DOMS is some of the chemical changes in our muscle caused by the exercise bout. We’re not talking about lactic acid here though, which is often accused of being a contributor to DOMS. We won’t go too much further into the science here but we’re talking about an increase in hydrogen ions that occur when we exercise. This metabolic stress plays an important role in our recovery as it leads to inflammation. Inflammation has quite a bad reputation but is also very important in aiding recovery and adaptation. These chemicals and inflammation are picked up by nerve endings that tell our brain that something hurts. Our brain is kind enough to then let us know this! Much like inflammation, DOMS is part of the important cycle of repair and growth and as we’ll discuss later we should consider carefully whether we want to eliminate it or not.