Sure Tony, but how would you explain those young Japanese kids (and not only Japanese) being so successful nowadays? Before 40+ era, Zhang Jike needed those huge leg muscles to "take the power/spin from the ground". The swing had to be larger. Now all trainers suggest short, compact move for the fh stroke ...
I'm sure I said it somewhere
the only players in the top 50 that isn't injured is pretty much your youngsters.
firstly with Japan, it is of many factors:
1) these kids are younger and learnt for the 40+, compared to your Ma Long, Xu Xin (30 year olds) that learns 40mm and had to change to 40+. Throughout history we can see how many world champs struggle with the transition, this is normal.
Every rule change basically has ended careers for some.
2) Japan had unlimited budget for Tokyo 2020 olympics games. and the approach is 1 player appoints his/her own manager and that manager has full control on how the money is spent.
they will appoint the players own coach/training partners, staff/medical etc
You saw what happened with China 1 coach many players system - some players will not get attention. Japan has been doing this for 6-7 years already (15 juniors chosen with unlimited budget)
3) you said it yourself, new style of coaching suggest shorter shots - to prevent injury and to add efficiency in getting ready for the next stroke - the rallies are much longer
a lot of the younger players are learning this, while the older players much unlearn and relearn.
So, now my question is - how long will the younger player last?
they may seem fit and less injury to your older's today
But the body is a machine, eventually it will break down.
From most of the national team coaches I have came across, they all are worried about the amount of injuries.
I know one that is prone to injury in 40mm, and got worse with 40+ has pretty much ended his career. He was a world100-200 quality. His injury was shoulder.