We’re all crunched for time, so squeezing in a daily workout — even a quick one — can be a real challenge. That’s why everyone wants to get the biggest bang — and burn the most calories — out of each workout. I get it. But a quickie is NOT going to cut it.

Sure, there are some studies that’ll tell you that working out for ten minutes in the morning, ten minutes at lunch, and ten minutes at night is just as good as working out for a solid 30 minutes, but that’s crap. While it’s great that you’re fitting in exercise when you can, you’re not burning as many calories when you break it up this way. You have to exercise for an extended amount of time to release fat-burning hormones like HGH (human growth hormone) and testosterone, which help to kick-start the afterburn effect.

Afterburn describes the boost your metabolism gets after a workout; in technical terms it refers to your body’s post-exercise oxygen consumption. It’s what helps you continue to burn calories at a faster rate — and it can last anywhere from 15 minutes to 48 hours, depending on the intensity and duration of your workout.

But those short ten-minute bursts of exercise won’t get your biochemistry fired up enough to release the necessary hormones that initiate afterburn. So, yes, you’ll still burn the same number of calories during your ten-minute stints, but you’ll be shortchanging yourself when it comes to the number of calories lost as a result of afterburn.

Obviously the longer you work out the more calories you’ll burn and the better the afterburn effect. I know not everyone has time to commit to an hour-long workout, but you need to bump up any ten-minute chunks to 30 straight minutes for optimum calorie-busting action. (All right…if some days you really can’t manage 30 minutes in a row, you’d better at least give me a solid 20.) And you know what would really get me amped? Knowing that you’re completing a 45-minute routine. Once you’re in the zone, what’s an extra 15 minutes anyway?

Duration, however, is not the ONLY key to weight loss. intensity, complexes, HIT, and circuit training are all integral tools for shedding fat fast. These are my three foolproof ways of getting the MOST effective fitness and the MAXIMUM calorie burn out of a “fast” (30 minutes most days, but 20-minute minimum!) workout:

1. Intensity: If you’re going to work out for only 20, 30 — or 45 minutes, always do it at high intensity. Get your heart rate up and working at 85 percent of your maximum. Make sure you’re working out so hard that you SWEAT your butt off. The ONLY time I give you permission to decrease the intensity is if you feel that you’re working too hard to maintain proper form, which is a sure path to injury.

2. Multiple muscle-group combinations/complexes: When you combine a number of different muscle groups into the same exercise, it’s known as synergistic core-based training. Hybrid lifts or combo lifts, in which you are using your leg muscles to do squats or lunges while lifting dumbbells or a body bar, are a good example of this type of workout. The cool thing is that when you work out this way, you don’t need to focus on your legs, and then your core, and then your abs because you’re already doing them ALL at once. And best of all, the more muscle groups you recruit into the exercise, the more calories you’re burning.

3. Circuit training: This type of workout keeps you moving from exercise to exercise with no rest in between. For example, if you’re doing push-ups, you’re incorporating your shoulders, triceps, chest, and abs, and then you can go straight from your push-up set into a set of lunges. You’ve changed the muscle groups you’re working, but you haven’t stopped exercising. Now, this is where intervals come into play: You add high-intensity training (HIT) into the mix by throwing an intense cardio interval into your resistance-training circuits. For example, you add a minute of jumping rope, sprinting, or doing jumping jacks to jack up your heart rate and burn a ton of calories, and then you go back into the resistance-training sets. This way, you maxime BOTH your time and your calorie burn.

Put these three techniques together in a fast 20- to 30-minute period, and you’ll have the most effective workout for burning the greatest amount of calories EVER.