Jovana - that is a very big question. The answer depends on a lot of factors. Can you tell us how old you are and what are your goals?
Do you want to race and if so would you race long distance?
How long have you been riding?
Most athletes will train at lower heart rates (60 to 70% of mhr) in the non-racing season. This allows for development of the aerobic system while still working at an intensity that allows for easy recovery. As you approach racing season, the intensity of your rides should increase. So it really depends on where you are in your training and where are you going with it.
I use the "Triathletes Training Bible" by Joe Friel to guide my training. It's a very good resource and I believe he has a similar book for cyclists.
This may be a good place to start looking around:
http://www2.trainingbible.com/
If you give us some more details, we might be able to help here on TE.
Living life like there's no tomorrow.
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2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
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