I started doing a slight tweak to my workout routine.

I do 1 set per exercise, and push to do 20 reps of that set. If I don't make it, I rest for 30 seconds and try to squeeze out some more, and repeat until I hit 20 with minimal rest.

I write down the weight and the number of reps of my first failure. When I can make it to 20 reps without failure, then the next workout I up the weight. It works really well, and I can do a full body workout in under 45 minutes and get great gains thanks to really tapping out each muscle group.

Doing heaver weights and less reps tends to cause more injuries for me (I am 46) and I always found I had plenty of gas still in the tank when I did drop sets, so I knew I wasn't really reaching my limit. This makes it so I can reach my limit without having to pull off plates and do lots of sets. It also gives an clear goal - 20 reps every time, even if you have to take mini breaks.

Research has shown that number of reps is not really that important to muscle growth - what is important is pushing to failure, and this seems to really get me to that failure. If I can't even do another rep at what should be a fraction of my 1 rep max, then I know that I have reached true failure.

Update 2024-05-31

Well, I started hitting walls with 20 reps for arms. It just is hard to get to 20 at the limits of what my arms can do, but using rep/weight calculations of the higher amount for 15 reps, I am able to achieve and upgrade my weights, even when I have been stuck for weeks at the limits of what I can do at 20.

This only seems to apply to arms though. Legs and back seem to adapt just fine to upping weight at 20 reps, and haven't had problems there. My theory is that large muscles have a higher ability for long term stress. The little biceps and triceps just can't keep going.