To jump right to the answer, never (with some very rare exceptions). I very often, however, see exerciser who need to stop immediately what they are doing. Most of these are simply well-meaning folks who haven’t a clue what they are doing.
I believe that most people want to exercise, but they don’t know how. This is due, in part, to exercise professionals who want to seem scientific with intimidating words and phrases—like “metabolic conditioning” and “mitochondrial hypertrophy”. The reality is that the basic principles of exercise are quite easy. (Nothing too challenging about progressive overload and specificity.) It is the implementation that is hard. Learning, practicing, and mastering proper technique challenges us all.
So, when should one stop exercising? When they are wasting their time or, more importantly, when they are going to hurt themselves.
I have often heard the phase: “at least they are doing something”. That, of course, works in some situations, but the more I watch people “doing something” the less I want to see them “doing something”.
Some people get lazy with their technique and get habitually sloppy. Other people just haven’t had good teachers—they are self-taught or learned from the wrong people. Some lousy coaches talk a good game, but know very little. Some great coaches are simply uninformed.
I recently read a conversation between trainers about “altitude masks”. One is a well-trained, well-informed, effective coach. The other was someone I did not know, but who seemed well-educated—he certainly had an understanding of the bioenergy systems (i.e., glycolysis, lactate, ATP, etc.—the basic nightmare of any exercise science student)—though lacking in the fundamental application of his knowledge. As such, it is difficult to know whose knowledge to trust.
It is not enough to know how. One needs to know why. A good coach/trainer gets results. As an exerciser looking for a qualified trainer, it is not enough to find a coach/trainer who is in shape. I have seen a lot of in-shape people who were a whole-lotta stupid. On the other hand, my first mentor was a man looked like the last person who you would have any knowledge of strength and conditioning. Look for trainers who are educated and certified, but also experienced.
Bottom line: learn how to exercise and practice good exercise technique. The results of training are only as good as the effort put in. Stop exercising poorly and start training with a plan.
Be your best today; be better tomorrow.
Carpe momento!