I loved riding and racing my bikes and i was as skinny as anything in those days. if i did a 24 hour race i would lose a stone in weight even though i would eat every hour. I wouldn't believe the it won't hurt your joints though, After 20 years riding and racing i've worn both my knees out and i have rheumatism in both hips which is why sadly i can no longer ride a bike, or at least one that hasn't got an engine. Defiantly the best times of my life though and i feel more stress at work and i don't sleep as well since i've stopped.