Good question. There are those who say No, that working out when sore will impede recovery, and there are those that say Yes, and accuse the No-people of looking for excuses not to work out.
As is often the case, the truth is somewhere in the middle. If, days after a workout, you have muscle soreness to the extent that you can't perform daily tasks, you probably went too far. If, however, you avoid hard work like the plague in order to remain completely free of muscle soreness, well, that's not good either.
It's important to understand what muscle soreness actually is. The type of soreness discussed in this article is called Delayed Onset Muscle Soreness (DOMS). When you exercise (and by "exercise," I mean actually become physically exercised, not passively moving without any real exertion), your muscles are withstanding microscopic tears in the muscle fibers.
These tears create the sensation of DOMS. With proper recovery and nutrition, these fibers rebuild themselves. This is what produces new muscle. Ah, new muscle.
Pretty straightforward. So that brings us to the key question: should I work out when my muscles are sore?
It's important to ask yourself, "just how sore am I? Am I wincing in pain every time I stand up or go to wash my face? Or do I feel merely a faint echo of what the soreness was a day ago? The answer is clear in either of these two scenarios.
But what about when your DOMS is somewhere in the middle?
There can be a certain trade-off by working out when your muscles are moderately sore. You shouldn't expect them to work at full capacity when they are in the process of recovering from a prior workout. But, in many cases, a missed workout can ruin an otherwise healthy fitness routine, or hamstring long-term results. So the benefits may outweigh the costs.
DOMS can be a somewhat frightening phenomenon to new exercisers. Unfamiliar movements tend to produce more pronounced DOMS, and to a new or out-of-shape exerciser, every exercise is unfamiliar. It is easy to mistake DOMS for an injury.
As we experience DOMS again and again over our fitness journeys (and anyone doing fitness can experience it at any phase, novices and veterans alike), it becomes easier to handle both physically and psychologically. It can become the hallmark of a good workout and a symbol of progress.
However, it is important not to become fixated on it. DOMS may not occur after a workout, but that does not mean the workout was wasted. This is especially true when the exercises are familiar, such as for someone who squats every Wednesday morning without fail.
As you move forward in your fitness journey, you will undoubtedly experience the divine agony that is DOMS. You will learn how to anticipate it, mitigate it, deal with it, and, by extension, to know when it's safe to train in the midst of it.
Happy Hurting! (but not too much!)