Proper training load is a controversial and interesting topic. Over the years, I’ve learned a lot about it.
The body can adapt to great stress, if it is allowed to adapt slowly. Training must be directed towards specific goals, of course dependent on the particular sport involved. If you want to be good at heavy singles in certain lifts (weightlifting, snatch and clean & jerk), you train heavy snatches and C&Js. Certain lifts can be trained more frequently than others, limit snatches vs limit dead lifts, for example.
Reaching elite levels without performance enhancing drugs is almost impossible. I’ve had some interesting conversations with some Europeans (“you cannot train without restoratives”) and Chinese coaches (“Chinese medicine” smile and nod).
I found myself sitting next to Alexander Medvedev (USSR, world champion and later national coach) at a world championships. This was after he retired. I wish I spoke Russian, or he better English. He did impress upon me he was a Professor of Sport and taught at the university. The Russians have studied overtraining extensively. They used regular blood tests, though I couldn’t get out of him exactly what they tested. Also, daily, or more, blood pressure checks. BP checked first thing in the am, ideally before getting up. A 15% increase from the day prior meant a light day was in order due to lack of recovery.
I think blshaw had a good point, most have no idea what it is like to really push themselves. Even some elite lifters. I saw a guy absolutely smoke a 300kg x 5 back squat, could not have done them faster. He was probably faster than I was with 200kg. Racked the bar, “those were really heavy. I think I’m through.” I would have bet on 350x5. Over the years, I’ve often seen someone make that last rep easily, only to declared they don’t have another one in them, or another set.
As an aside, I have obtained blood work from some elite weightlifters (not from US, I can’t name names so systemlord will have to remain skeptical) and was shocked to see some pretty low testosterone levels, in the 300s. These guys were not using any androgen suppressing PEDs. I guess what they were using offset the low test. It is known that overtraining can suppress hormones, but seeing these levels in guys lifting what they did was hard to believe.