Hey Jessica. I would guess it has to do with your fitness goals. That first month is geared towards getting your muscles ready for some heavy lifting. Any cardio you do might prevent you from gaining muscle because it uses both fat and muscle. The progression of the 12 weeks is meant to build as much muscle as possible, so that in the 3rd stage you can cut fat (ie. Burn calories through cardio) and not worry about losing as MUCH muscle. Also, more muscle burns fat throughout the day, so itís good to initially spend your calories on muscle growth.
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