A nice article below from STACK. It is my experience as well, pushing to failure too often leads to a fried CNS and injury. As one of my great coaches, L.Jay Silvestor used to say, "You should feel like a Tiger after your workout." He meant you should feel stimulated, not annihilated.
Updated: August 13, 2019
A common misconception in strength training is that lifting to failure is the ultimate way to get bigger and stronger.
After all, that's what hurts most and feels hardest. And in many people's minds, harder is always better.
Doing a set until "failure" means allowing fatigue to accumulate to the point where performing even one more rep with proper technique is impossible. Exactly how many reps it takes to go until failure depends on numerous factors, including the load, the choice of exercise, your particular strength level, etc. If you aren't going until failure, then you're finishing a set with "reps in reserve," which means ending a set when you still are physically capable of doing one or more additional reps.
While there's a time and a place for training to repetition failure, doing so too often has been scientifically proven to result in diminished gains in strength, power and hypertrophy.
Why 'Too Many' Reps Is a Real Thing
Advocates of frequently training to failure often cite that it is necessary to drive adaption and push the limits to get results.
The issue with training to absolute failure with respect to building maximal strength is that it causes neural fatigue and disruptions in resting hormonal concentrations. Athletes and recreational gym goers repeatedly pushing themselves to the point of failure during a training session set themselves up for an inability to properly recover and repeat performance over the next few days. In a phase where one is seeking to gain strength, they will find that they are gradually becoming weaker and more fatigued as they continue to consistently push to failure. Thus, they're simply incapable of regularly moving the weights needed to sustainably enhance max strength.
This strategy also greatly enhances the risk of injury and often leads trainees to eventually avoid heavy strength all together with the belief it makes them stiff, tired and hurt.
When seeking hypertrophy, reaching absolute failure is less detrimental from an injury, hormonal and neuromuscular standpoint. However, making it a staple of your training is still quite counter-productive. It can lead to overuse, excessive muscular damage, and other similar peripheral issues.
As strength and conditioning researcher Chris Beardsley notes in his article on the topic, "sets with light and moderate loads can probably be terminated a couple of reps before muscular failure (1–2 reps in reserve) and still produce meaningful amounts of muscle growth. For some trainees, this may be helpful, since training with a closer proximity to muscular failure increases muscle damage, making it harder to train more frequently."
Why 'Reps in Reserve' Reigns Supreme
If you resist the urge to bury yourself by always reaching for that "last rep," you will be rewarded.
The most effective method of training is the incorporation of the idea "reps in reserve" (RIR). When working with a percentage of your one-rep max, there's a max number of reps in a set you should theoretically be able to perform. When the percentage is 100%, that number is naturally one rep. For something like 75%, it's 10 reps. Theoretically, attempting that 11th rep would result in failure.
If this is indeed the case for you, working with reps in reserve would mean cutting that 75% set short at 8 or 9 reps instead of 10, giving you rep(s) "in reserve."
While it might seem like "quitting" on the set before you've given all you have to give is bound to result in inferior gains, the opposite is in fact true. And this fact appears to be valid with nearly any rep range.
In 2011, the Scandinavian Journal of Medicine and Science for Sport presented a study that examined two subjects performing Squats at ~80% of their one-rep max. Subject 1 quit squatting when his movement velocity decreased by 20%, while Subject 2 quit squatting when his movement velocity decreased by 40%. Thus, Subject 1 finished his sets with a significantly greater number of reps in reserve. These two subjects followed the program for several weeks, and the results were astonishing. Despite Subject 2 completing more overall work and pushing himself closer to failure, he encountered a significantly lower gain in strength than Subject 1.
Related research has found similar results for measures such as power, vertical jump and rate of force development. For muscle growth, any additional hypertrophic benefit of consistently training until failure is usually outweighed by the fatigue and excessive muscle damage this typically causes. Thus, training with one or two reps in reserve generally gives you an edge in volume load over the long term. Basically, always going for "one more rep" simply isn't worth it.