You're right. Alot of females are scared to do any resistance training e.g weights because they think they'll get big/bulky. People have no idea how much time and effort it takes to put on muscle. Over eight years I've put on about 21kg and am now just starting to plateau.
The fact is muscle burns energy. So if you're looking to re-shape your body and burn fat faster you need the resistance training. I eat a shit load of good and bad foods but don't gain any fat (it's rad).
But yeah a good mix of cardio and weights is perfect for getting fit for riding and as has been said riding itself is probably the best way to get bike fit. Remember rest is just as important.
I heard those '300' workouts were pretty brutal. Do you get to drag things and lift tyres?
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