Spinning while going at low speed looks ridiculous. Often one sees it with people on MTBs
At one time, spinning purposely at higher cadence (~100) I developed a burning behind my knee cap on one leg that a month of taking it easy cured it. I'd say, both mashing or spinning can lead to problems but usually it only brings out potential problems that are already there, not causing them.
Spinning uphill taxes ones aerobic reserves more than mashing it unless maybe you train specifically for that. If you have spindly legs like Froome, spinning is your only option.
As one gets older, it helps doing home exercising for firming up your knees, like small jumps when your knees don't bend too much, that sort of thing like what male ballet dancers train.
Last edited by vane171; 05-05-21 at 11:43 AM.