Should You Train To Failure?

If your goal is targeting a specific muscle and you stop feeling that muscle due to various compensation mechanism it stops being effective and I personally would stop the set at that point. This is mostly applicable to more targeted movements like single joint or machine exercises.

With more complex movements it see technical breakdown as the end of the set. Keep in mind that I’m talking about significant breakdown like turning a squat into a goodmorning squat or lifting the butt off the bench.

In both cases, while it will vary depending on the exercise and experience level of the lifter, this typically falls at a point where you have 1-3 reps in reserve were you to accept continuing the set with those compensations.

Very rarely do I recommend movement (true) failure; except, for example, on single joint/machine exercises if it coincides with tension failure which is the case with advanced lifters with great mind-muscle connection. – Christian Thibeadeau