frequency and duration of cardio-exercise for bodybuilders  

as far as frequency is concerned, 2 to 4 sessions of 20-40 mins. each for male bodybuilders in the off-season is recommended. if a contest is approaching, then gradually increase the activity to no more than two session per day, 7 days a week of 45 mins. each on the worst case for a short period of time. remember, it is those long hours of cardio-exercise that cause bodybuilders to look like POW's in the bodybuilding stage the day of the show. if you are doing 2 sessions of 45 minutes of cardio-exercise everyday make sure that you take plenty of glutamine (15-20 grams) in addition to having at least 7 meals per day.
for women, due to their higher concentration of estrogen in the blood and due to the fact that they have less muscle mass that male, more frequent cardio-exercise is benefial. therefore, off season plan of 4 to 5 sessions of 30 -45 mins. and if a contest approaches is highly recommended and gradually increase the activity to no more than two session per day, 7 days a week of 45 mins. each on the worst case.