[flamebreath447]

There are a couple different definitions of failures

Mechanical failure - your form is being compromised, usually induced by muscular load

Throughput failure - you could maintain form but your cardiovascular capacity is the limiting factor and you are starting to decrease in tempo (either in the eccentric or concentric)

Partial Failure - you use assistance on the concentric or eccentric to continue to do the one that’s still has workload capacity

Each type of failure induces a different level of lactic acid build up, or muscle tearing, and can be increased in different ways. Usually one of them is a limiting factor and is why progressive overload is proven to improve strength and size.

Most of the people I’ve worked with don’t know true failure (within 1-2 RIR [reps in reserve] left) because they’re limited in cardiovascular capacity to even reach failure or they aren’t pushing themselves due to fear of form breakage/injury.

The reality is you shouldn’t be doing 1 rep maxes often, but you should be lowering the weight and experiencing true failure in order to progressive overload properly.