So I had a question about weight lifting with biceps and how the fuel is provided. Muscles use ATP for fuel. This available atp is constantly being replenished with the glycogen in the muscle, when the glycogen in the muscle runs out, or while it's being depleted, it's actively being rebuilt from blood.
I noticed at first I can easily go for combined weight of up to 120 lbs for bicep curls. I'll do the highest weight I can for 10 sets every 3 minutes. I'll also super set with bench press while im waiting for the three minute rest period for my biceps to expire.
After 40 minutes I'm noticing the maximum weight I can lift drops to 60 lbs combined for bicep curls, and then at 60 minutes, I can't lift any weight. I can, after the 3 minute waiting period, lift 90 combined for 3 reps, but then after that I instantly run out of power and can't lift my arms.
I know that it would take 1-2 hours of running or heavy cardio for the body to run out of glycogen. I would like to think that this is what's happening here but I am skeptical about it so that's why I'm asking.
Can something else be happening here? like maybe the nervous system wearing out over the coarse of a workout? Or is this a normal condition happening to muscles because of some anatomic processes? Could my arms be very weak even while being full of glucose and ATP?