You know those days ,when you’re tired and not only you can’t do your usual set of reps/lifts but you also do less than usual (not because of lazyness,but because you’re truly tired)
Are these days still useful for muscle growth or is it just a waste of time ?
It will hurt you in the long run, because if you have already trouble regenerating for whatever reason, exhausting your body even more won’t do any good
Although there are training concepts of so called controlled overtraining, these are quite advanced and should only be applied by experienced athletes.
I agree with the posters above, if you are really feeling tired you should rather take a day off.
on days i just cant get into it and feel like really really off ill just do more accessory work like rotators and abs and maybe some arms, and not sweat the big compounds, maybe do some stretching in my hams for a while for a deeper squat the next day