MYTH: The Longer My Workout, The More Benefits I Get

Celebrities spend countless hours a day getting in amazing shape for a role, and it's hard not to compare your workout regimen with theirs. But is a three-hour-plus workout session any better than a killer, hour-long one? It's time to find out.

The Truth: Exercising at a high intensity for 30 minutes is a perfectly effective way to work out.

When it comes to fitting exercise into your busy life — the key is to make it happen. Does it need to be a 90-minute yoga class or a 60-75 minute DVD workout like P90X or Insanity? Absolutely not. If you only have 30 to 45 minutes to train, here are some rules to live by.

Your workouts should be no longer than two hours. Most of my DVDs are 30 to 45 minutes for a reason — that’s the appropriate amount of time I want you to spend working out intensely, at least four to five times a week. That range is also recommended by the World Health Organization (for adults ages 18 to 64). In fact, when you exercise for more than two hours straight — even at a moderate intensity, your body releases stress hormones such as cortisol, which inhibits weight loss, causing your body to react by storing fat and retaining water out of self protection. A recent study published in the American Journal of Physiology found that 30 minutes of daily training provides an equally effective loss of weight and body mass as does a 60-minute workout.

Your intensity counts more than the length of your workout. Have you heard of HIIT, or high-intensity interval training? It’s time to get familiar with the term. HIIT is an exercise strategy that alternates periods of short, intense anaerobic exercise with less-intense recovery periods. HIIT burns more fat and creates a greater afterburn (a word that describes the excess post-exercise oxygen consumption, or calories expended after exercise) than steady training at a lower heart rate does. To perform HIIT, you want to workout at 85 percent of your target heart rate, and then recover. Mountain climbers, butt kicks or high knees are great HIIT exercises to work into your daily circuit-training routine (circuit training works different muscle groups with short bursts of resistance exercises using moderate weights and frequent repetitions). When you’re using HIIT on a cardio day, perform 30 seconds of max intensity, followed by 30 seconds of lower intensity.

Cardio sessions count as extra credit. A 30 to 60 minute cardio workout is enough to accomplish your weight-loss goals. In my books (and real life), I advocate four sessions of resistance training a week and then explain that cardio is extra credit. By adding cardio on two more days a week you will increase your weekly burn, thus accelerating your weight loss.

The Bottom Line: A 30 to 45 minute workout, five times a week, is the ideal way to manage your weight. If you want to lose weight at a faster rate, add more cardio to your routine, but never exceed two hours in a single workout session.