You have to remember that rest is part of training.
About diet, Sondre eats normal food, especially pasta and rice, and a lot of vegetables and fruit, with not too much proteins of animal origin (meat and eggs), that are introduced with milk only.
About stretching, he (and my athletes of every Country) don't use frequently, because my opinion is that too much stretching is not only useless (good for wasting time), but sometime also damageous, since with too much "static stretching" we reduce our reactivity. He uses sometime "dynamic stretching" that is something different, and some exercise of mobility.
About sleeping, he sleeps about 8-9 hours per day, with a short rest (about 1 hour) after lunch, before the second session of the day.
My opinion is that the body, if trained with graduality, can raise the level of intensity in any activity, making normal what before was not possible. For that reason, one of the most important rules for athletes is "never losing what they already have", and this is the big difference between the training according to Lydiard and the modern training.
At the beginning of Sixties, the activity for a top runner was consentrated in few months every year : there were not WCh, Olympic were every 4 years, and in the middle there were the Area Championships (European or Commonwealth Games).
The odd years were practically empty : big meetings didn't exist, there were no marathons or road races of international level, the only activity more developed was Cross Country (but not in Oceania).
This calendar allowed athletes to use long periods of general preparation, and the level of intensity in their training became
very much lower than the level at the top of their best seasons.
Today, the activity of the best runners lasts all the year, and the most significative choice is to maintain a high level of intensity in training during all the seasonal periods.
This choice brings the athletes to two different situations :
a) Under organic point of view, they continue to grow for several years in their career, of course if are able to have continuity in training and the right dosage of quantity and intensity. Don't forget that training is the answer of the body to some stimulus, and stimuli can be in two direction only (extension and intensity). Compared with the past, the methodological goal in the modern training is to INCREASE THE VOLUME OF INTENSITY during a full career (not the volume at low intensity, and not high intensity with little volume).
b) Under the point of view of the body structure, we have more consumption, but at the same time more adaptation to high level of intensity, and this goes to reduce the possibility of injuries (on the contrary of what people normally think), because injuries deriving from training (so, not connected with accidents) are more frequent when there is high intensity without right preparation (so, we have a stairs with many stairs, very close one another, and we have to use ALL THESE STAIRS, not only some of them. Every stair is, for example, a different speed, remembering that few seconds per km at the end represent different stairs, and running at 5' or 4'50" per mile is a very big difference for the body).