my_cardio_routine

I do cardio only when I am attempting to lose fat. The goal is to burn calories from fat while perserving muscle mass. I do cardio 4-5 times a week for about 30 minutes with my heart rate at about 65% of the max. Any longer than 30 minutes and the body will start to use muscle for energy.I watch my heart rate very closely because this determines what is being used for fuel in my body. The following table displays this.

Since it is next to impossible to possess a ripped and lean body while adding any substantial amount of muscle mass, most bodybuilders follow an on/off-season diet and training plan. During off-season training, cardio should be limited to once a week to ensure all possible calories are used to build as much muscle mass as possible. However, during the on-season, cardio should be performed up to 4 times a week to eat away at bodyfat stored during the off-season.
Cardiovascular exercise is one of the most important keys to
getting that well defined, muscular physique. Similar to resistance
training, there is science involved with cardio to heighten its results.
The amount of bodyfat lost is in direct relation to the number of fat
burning elements you zero in on. The following three parameters are
keys to effective cardio workout.

1. Timing - It is most effective to perform your cardio session when you first wake up in the morning, on an empty stomach. It is best to perform cardio on an empty stomach because your body will tap into its fat stores for energy, instead of having to burn carbs and then start burning fat. Although this is the ideal timing for cardio, it may be just as effective late in the afternoon if a proper diet is followed.

2. Intensity - Intensity for cardio is defined as the percentage of your maximum heart rate used while performing a particular exercise. To burn fat most effectively, you want to try and hit approximately 65% of your maximum heart rate. This is known as the ideal fat burning zone. To determine your maximum heart rate, subtract your age from 220 and multiply it by 0.65. This will be the ideal number of heart beats per minute to maximize fat burning benefits from your cardio.

(220 - your age)(0.65) = Ideal heart rate for cardio

3. Duration - If you're a bodybuilder, chances are you aren't doing cardio to become a marathon competitor. Cardio is used by bodybuilders to help increase oxygen flow to muscles and burn excess bodyfat. For best results, cardio should only be performed three to four times a week, on non-resistance training days. You should increase the length of your cardio session by 5 minutes each week until you reach a total of 30-35 minutes. This is about the maximum amount of time that the body will use glucose from carbs as energy. After glucose from carbs is all used up, the body will start decomposing muscle to use as glucose for energy.