I constantly check in with my clients by asking, How do you feel? or On a scale of one to ten can you tell me where your muscles are? Or I can watch their faces and know when the last rep is the last rep!
There is no point to train to “fatigue” or “go for the burn” anymore, particularly with older and new clients. It only adds to frustration.
I would let them know they will feel a fatigue or heavy feeling with the weights, or get to the point where they can no longer continue to do the exercise with proper form. You can usually watch the expression on their face as well, that will tell you about where they are. Sometimes, it may be hard for them to distinguish pain from burn.
Hope this helps.
I discuss what fatigue feels like – the weights feel heavier and/or it takes longer to complete a repetition because they’re getting tired. They might be able to “feel” the muscle that’s working, but it should be a general feeling in the region being worked, as opposed to a sharp or shooting pain like if they stubbed a toe or sat on a tack.
For clients that have really low body awareness, I watch their form closely. One sign of fatigue is deteriorating form; a client will “cheat” in order to recruit other muscles to help them do the movement. If a client has been properly doing an exercise and then starts to cheat, I consider them fatigued and have them cease that exercise.
particularly when working with older adults, I do not ‘go for the burn’ at all. I instruct them to go to the point where they feel tired and the weights seem to get heavier. Unless it is a previous muscular injury, I draw a distinction between sensations in the muscles vs in the joints themselves.