Back in Soviet times there was a trend in Sci-Fi depicting the bright communist future when people changed professions every few years or so, often between manual and intellectual, to stay sharp.

Interesting parallel I was unaware of. On a personal level I have found it very useful to alternate between mental and physical work for the sake of endurance. If I was mentally tired I could usually still do physical work. This was helpful within the scope of a day or week and I imagine that such alternating also aids longterm endurance.