You need to be objective about your performance. If you're not progressing, it might be time to take a break. Recognize when you're overtraining or taking on too much, and allow yourself to rest when necessary.

Most people can only sustain high-frequency training for about 4 to 8 weeks before needing a deload due to accumulated systemic fatigue.

Training to failure can lead to greater muscle growth but also increases fatigue significantly, so it's important to balance intensity and recovery. Going from some number of reps in reserve all the way to failure in a single mesocycle is a good practice for many, but not required; you can go two or three reps in reserve as long as you do enough sets to achieve close to ideal hypertrophy outcomes.

Advanced lifters often need to deload after heavy lifts like deadlifts, which can be extremely fatiguing, sometimes only training heavy once every two to three weeks.

To determine if you're doing the right amount of volume, consider how many sessions you have per muscle group in a week. If you're training your chest twice a week and feel fully recovered before your next session, you can increase the number of sets you do.

You should rest between sets until your cardiovascular system is mostly recovered, you feel strong again, and your synergist muscles are not limiting your performance. If your target muscle is ready to perform at least five repetitions, then it's time to go again.

If you're doing something like nine sets for biceps, that's totally cool, but you just have to train them less frequently to allow for recovery. If you're doing 15 working sets for just your biceps in one session, the literature suggests that's not optimal because your last sets may not provide effective stimulus due to fatigue.

Beginners can train for a year without needing a deload because they don't accumulate enough fatigue due to their lower strength levels.

The stimulus to fatigue ratio is crucial; it measures the effectiveness of an exercise in relation to the fatigue it causes, helping to determine which exercises are worth doing.