The All-or-None law is the principle that the strength by which a nerve or muscle fiber responds to a stimulus is independent of the strength of the stimulus. If that stimulus exceeds the threshold potential, the nerve or muscle fiber will give a complete response; otherwise, there is no response.
Injuries from other sports and Father Time has took away the real heavy weights. I had to rethink high intensity. I tried high volume less weight etc. but just could not get into it. I started back high intensity low volume and failure with lighter weights and 30/60 second rest with descending sets. After my 30/45 minutes I am done in all phases.