I have a bad habit of turning the peddles at to low a cadence. Forcing the peddles with brut force against spinning has caused me knee problems. This year I've been making conscious efforts to make use of all the gears and spin instead of grinding. My knees are feeling so much better for it.I feel that grinding away in to high a gear increases muscle strength but it puts extra pressure and strain on your knee joints ect. I could also imagine you would also wear out your chain and cassette quickly to. My old Peugeot bike which I've been slogging high gears on through the winter has got a worn out cassette now on just one gear. If i would of used my gears more efficiently the cassette would still be in good order