I just read an article in a bodybuilding magazine thatsaid all you need to lose fat is three days a week ofcardio for twenty minutes. It said that low intensity,long duration cardio workouts are not the best way tolose fat and that a high intensity twenty-minute workoutis more efficient. Is this true? I don’t have a lot oftime to work out so it would be great if I could get mycardio done in only twenty minutes.
Yes it’s true that higher intensity cardio workouts burnmore calories per unit of time AND increase metabolismmore after the workout than low intensity workouts.
High intensity cardio, including high intensity intervaltraining (HIIT), is very effective and time efficient,(although it’s not for beginners or those with certainhealth problems).
It’s common sense if you think about it – work harder,burn more calories, right?
Here’s where the confusion has come from:
It’s well known that low intensity exercise utilizesprimarily fat as fuel and high intensity exercise utilizesmore carbohydrate as fuel.
In the past, this was the basis for the idea that low intensity,long duration aerobic exercise was superior for fat loss. Somepeople were were afraid to exercise too hard because theythought it would take them out of the “fat burning zone” andmake them them burn only “sugar” and not body fat.
Today, research has proven that this belief in exercising ata low intensity to stay in the “fat burning zone” was false.At lower intensities, you burn more calories from fat, butyou burn fewer total calories.
For example, a 1995 study conducted by Grediagin, et al,published in the Journal of the American Dietetic Association(95(6):661-5) compared fat loss in two groups over a 12 week period.
One group performed exercise at 80% of VO2 max for a durationsufficient to burn 300 kcal, the other group performed exerciseat 50% of VO2 max for a duration sufficient to burn 300 calories(took a lot longer, of course). Hydrostatic body compositiontesting revealed that…
***each group lost an identical amount of fat.***
The authors concluded:
“This study suggests that fat loss is a function of energyexpended rather than exercise intensity. Therefore, if fatloss is the goal and time is limited, persons should exercisesafely at as high an intensity as tolerable to expend as muchenergy as possible during their allotted time.”
In my opinion, that conclusion pretty much hits the nail onthe head when it comes to answering the questions, “How long andhow hard should your cardio workouts be?”
Another study published by Ballard, et al in the same journal(51(2):142-6, 1990) showed identical findings. High (80-90%VO2max) versus low (40-50% VO2max) intensity rates werecompared in two groups with duration carefully controlledto ensure each group burned the same number of calories.
The high intensity group exercised for only 25 minutes andthe low intensity group for 50 minutes…
***both groups lost the same amount of body fat! ***
Keep in mind BOTH approaches worked, but the high intensitygroup got it done in half the time!
Regardless of whether your cardio sessions are 20 minutes,30 minutes, 45 minutes, or whatever, the higher the intensityduring that time period, the more TOTAL calories you will burn.The more TOTAL calories you burn, the more fat you burn.
Although many factors are involved in exercise-induced fatloss, the most important factor is the total number of caloriesburned, NOT whether the calories burned are fat or carbohydrate.
It’s also important to consider energy expenditure after theworkout, not just the calories burned during the workout.Higher intensities not only burn more calories per unit oftime, but they also elevate your metabolism more at restafter the workout is over. This post workout increase inmetabolic rate is known as “excess post exercise oxygenconsumption” or EPOC for short.
It has been proposed, based on the results of severalstudies comparing the amount of calories burned at restafter low intensity versus high intensity exercise, thatHIIT is a superior method of fat loss due to its effecton post workout metabolic rate.
Clearly, HIIT is the logical protocol of choice if you arehealthy, already fit and you have little time to work out.
However, it’s also logical that time permitting,more frequent and longer duration exercise might causeeven greater overall fat loss if intensity is sufficient,simply because more total calories can be burned overthe course of a week.
Remember, it’s all about the intensity and the caloriesburned, not necessarily whether the workout is peformedwith intervals or in a steady state.
For example, if you do 20-25 minutes of very intensecardio, you might burn about 400 calories. That’s a lotof calories for such a brief workout. But it only addsup to 1200 total calories in one week if your frequencyis only three days per week.
If you (gradually) built up your frequency to four, five,then even six days per week, you could double your caloricexpenditure to 2400 calories per week.
If you also increase your duration, your intensity willdecrease so you’ll burn fewer calories per minute, but thecalorie expenditure for the entire workout is higher, whichincreases your total weekly calorie burn even further.
Duration and intensity are inversely related, so the longerthe workout, the lower the intensity. But that doesnt meana 30 or 45 minute workout necessarily has to be “low” inintensity.
A 30 or 45 minute steady state workout can be “moderate” or”moderately-high” in intensity. The combination of the highestintensity you can muster with a 30-45 minute duration cancreate an enormous calorie burn. Some of that calorie burnwill occur after the workout as well, because studies haveshown that EPOC is influenced not just by intensity, butalso by duration.
Although infrequent and very brief (15-20 minutes or even less)HIIT workouts have recently gained great popularity (anddeservedly so), that doesn’t mean you should never do steadystate cardio, nor does it mean that certain individualsaren’t better off with longer, less intense cardio.
Respected organizations such as The American College ofSports Medicine (ACSM) still recommend longer daily andcumulative weekly exercise duration when the goal isfat loss.
The ACSM position stand titled, “The recommended quantityand quality of exercise” states, “A threshold level for totalbody mass and fat mass loss generally would require at least30-45 min of exercise per session for a person of averagefitness. If the primary purpose of the training program isfor weight loss, then regimens of greater frequency andduration of training and moderate intensity are recommended.Shorter duration, higher intensity programs may be recommendedfor healthy individuals at low risk for cardiovascular diseaseand orthopedic injury.”
To avoid overtraining, injury or aerobic adaptation, whichbecome risks with higher intensity, frequency, and duration,it’s important to build up slowly and ALWAYS get your physician’sclearance before attempting high intensity cardio.
naturally, of course, it’s not wise to dramtically increaseyour training volume or intensity suddenly, but rather toincrease gradually.
If your current goal is to maintain your level of body fatand stay healthy, I’d recommend starting with at least 20 minutesof cardio 3 days per week. If your goal is maximum fat loss,then time permitting, I would recommend higher frequency andduration, sometimes building up to much as 30-60 minutes5-7 days per week, if necessary, based on your weekly results.
Once you reach your desired percentage of body fat, then youcan gradually shift back into a “maintenance” program of lesserfrequency, duration and intensity. This is a form of “cardioperiodization,” similar in nature to the periodization ofweight training used by elite athletes. Staying on high volumecardio all year round is counterproductive and may lead toovertraining, aerobic adaptation and a plateauin fat loss.
Genetics also play a role in the ideal volume of cardio forfat loss. If you’re one of the few people who are geneticallyblessed with the fast metabolism and physical attributes toburn fat easily, then three days a week for twenty minutesoften provides sufficient stimulus for results. In fact, Iknow a few people with hyperactive metabolisms who stay rippedall year round without doing any cardio at all (I hate thosepeople, don’t you?)
The bottom line is that a single cardio workout prescription,such as “three days a week for 20 minutes” will not work foreveryone.Exercise programs must be developed on an individualbasis and they are not static. The frequency, duration ANDintensity all need to be adjusted based on your results.
If the intensity is high enough, three twenty-minute cardiosessions may be sufficient for you, depending on your goals,your current level of fitness and your actual results, butlonger and/or more frequent cardio sessions are sometimesa “necessary evil.”