After searching around the last few weeks, I've seen a lot of similar instances of this style of training. IPF powerlifters, namely the Russian national team, train with a ton of volume and moderate intensities (the Boris Sheiko programs floating around). Brian Siders, the only American with an IPF record, trains 6 days a week with insane volume.
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The authors apparently consider skill practice to be important even to the powerlifts - and that's also not unlike what Pavel Tsatsouline has been going on about: to consider strength as a skill to be practiced, instead of something to be "worked out".
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I'd also like to think that this kind of method, where you just suck it up and keep coming back for more punishment, is a useful adaptation in its own right. It fits in with Starr's comments about widening the base of the pyramid. It fits with examples like Bob Peoples (a farmer who was doubtless in excellent condition and able to tolerate and thrive on large amounts of work). It even fits with what I've always heard about the older Russian/Soviet methods, which emphasized having their athletes "in shape" in a general sense.
I don't know much about weightlifting, but a little about powerlifting- and since you have brought Sheiko and Siders into the picture I'll offer what little I know. Russian approaches to powerlifting are not at all about bashing yourself against a brick wall each week.
On my understanding, the general belief with the Russian coaches, Sheiko included, is that initially the greatest gains from training will come from reinforcing motor patterns and developing skill. Skill comes from repetition- in particular- the repetition of specific movements. The more specific the sport's movements the more specific the training needs to be. They recognise that different loading will produce different training effects- in neural-muscular terms- as will different rep and set schemes. They did massive amounts of research looking into optimal strength development and established that, in simplified terms, for the first few years of ones training life volume was the key. They recognise that different loads have different roles- for eg, 50% and 70% have different training effects- but also that a well rounded athlete needs to develop conditioning, muscularity, power etc- so they come up with a template that addresses all of these needs through a program.
Most Sheiko programs for beginners and novices work with the idea that building volume will build strength- not consistent high intensity work- and volume and intensity are always cycled in 4 week blocks. So while Sheiko programs may look like they involve an inhuman amount of lifting- the volume and intensity wave up and down to provide an optimal balance of adaptation and challenge. The intensity with lower rated templates is hardly ever high- in fact for most you only go over 85% on 2 occasions in a 13 week block- on week 9 and comp day.
There is certainly the view that the CNS, and the body in general, will adapt- but that in order for it to adapt you need to give it a chance to adapt. 'Overtraining' is hard to define. If you mean pushing yourself to a point where accumulated fatigue means your performance (in terms of power output or strength) drops- then the Sheiko approach is definitely all for overtraining- but then thats not 'over'-training is it- they see the development of stress in this form as being essential to the development of optimal strength.
One thing I learnt was that feeling strong in the gym was no accurate indication of how well I was building strength. Sheiko will beat you down then give you time to adapt. This is why I think a lot of people don't have the nuts for Sheiko- you spend about 50% of the training cycle feeling weaker and beat down.
Siders has said his routine is essentially a CMS Sheiko routine where he has introduced greater variation (so different types of squat, bench etc), which is in keeping with the approach of Sheiko- where move advanced lifters require less specificity as their skill level is higher.