How long is too long per lifting session?
Is there an ideal length of time for lifting weights? 1 hour? 1.5 hours (90 minutes)? 45 minutes?
The reason I ask is because lately, my lifting sessions have been getting longer (between 90 and 120 minutes). I've been trying a lot of new exercises and different set/rep ranges which explains the increase in time. I've also added traps and forearms at the end of every upper body workout (3x per week) because those were stubborn areas for me and hitting them 1x per week wasn't getting the job done - this has improved those areas but added more time to each workout.
By doing these longer lifting sessions, am I limiting my capacity for gaining muscle in the long run? Is there a certain point after which your body cannot handle anything more for the day (assuming heavy lifting for 3-4 sets of 6-8 reps per exercise) and any further exercise is actually detrimental? Maybe I should do 3 sets max, and skip the 4th set altogether?
Most importantly, can a longer lifting session actually start to cannibalize the body's muscle, assuming a heavy workload as described above?