In full contact competitive arts e.g. striking and MMA the trend has been toward more and more limitation of contact sparring. For striking and grappling arts like BJJ, you can still train skills with very low contact and low intensity drills so you could train many hours of the day sustainably. I have never practiced Judo but I am pretty sure due to the dynamic nature of throws there is no real way around throwing each other to train, i.e. the intensity or equivalent of 'contact' can only get so low.