While you make a nice argument for pain not being a unit of effort, I think a subtlety is ignored -- pain at the threshold of current capability is not differentiated from pain derived by trying to perform well beyond capability. The 20th rep of a 30 lb dumbbell curl hurts. But the pain doesn't endure. You have a meal, get some rest and recover. However, you risk injuring yourself if you attempt the same with a 100 lb dumbbell. While the former contributes to muscle growth, the latter causes injury. Both are painful, but the pain is different. Pain is cruc... (read more)
While you make a nice argument for pain not being a unit of effort, I think a subtlety is ignored -- pain at the threshold of current capability is not differentiated from pain derived by trying to perform well beyond capability. The 20th rep of a 30 lb dumbbell curl hurts. But the pain doesn't endure. You have a meal, get some rest and recover. However, you risk injuring yourself if you attempt the same with a 100 lb dumbbell. While the former contributes to muscle growth, the latter causes injury. Both are painful, but the pain is different. Pain is cruc... (read more)