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Can too much cardio slow fat loss?

Exercise is often recommended as a way to increase the rate of fat loss in a weight management program. Strength training is important for maintaining the lean mass, or muscle tissue that’s often lost by those who use only diet to lose weight. Endurance training, or cardiovascular training, is often encouraged as a way to increase the amount of fat energy used during the day, train the body to burn fat more efficiently, and help to increase the rate of fat loss.

The fact that longer-duration, lower-intensity activity burns predominately fat leads many people to believe that “more is better” when it comes to cardiovascular training. However, that may not be the case. A group of researchers, using a randomized, controlled trial looked at the effects of varying durations of cardiovascular exercise and the effect it had on fat loss for overweight men.[i]

The Study

Sixty-four overweight men were put into three different groups; a moderate volume aerobic exercise group (MOD), a high (HIGH) volume group, and a control group (CON). The workouts were completed on a daily basis. Three days per week, both exercise groups trained at a high level of intensity (70% of VO2 max). The other days, they trained at whatever intensity they choose. On high intensity days, the duration of the workouts would be shorter as the men burned more calories per minute than at lower levels of intensity. Participants had to exercise 80% of the days during their 12-week study.Those who subscribe to the idea that weight management is a product of monitoring calories in and calories out (or eat less, move more) would expect the group who expended twice as many calories through exercise would lose more weight. It didn’t turn out that way.

The result of the study showed that even though the high-volume exercise group burned twice as many calories as the moderate-volume group, and ate the same number of calories, both groups lost equal amounts of weight. Not only that, but the improvement in cardiovascular function, as measured by VO2Max, was similar for both groups, even though the high-volume group spent more time exercising. The moderate-volume group had an 18% increase in VO2max, while the high-volume group had a 17% increase. As you can see  based on the table above, the high-volume group burned far more calories, spent far more time exercising, and ended up in about the same spot with body composition. Actually they averaged 1% less fat loss than the moderate group.

The study authors did not point it out, but during the 12 weeks, the higher-volume exercisers averaged three days of being sick instead of one for the moderate group as well. Based on this study, they could show the higher-volume of endurance activity tripled the chance of getting sick, though additional studies might be necessary to investigate this more.

How could this happen? If they expended more calories, they should lose weight faster, right? Not quite. Looking further into the study, the higher intensity group actually increased their lean body mass and resting metabolic rate, which is different than the experience for the moderate group, which lost some lean body mass and saw a reduction in resting metabolic rate.

If you’re following along, this is what the study showed:

Moderate Group versus High Group: Half the exercise volume, about half the calories burned, reduced lean body mass, reduced resting metabolic rate, slightly greater fat loss.

How could this be? An interesting finding was that the moderate group was more active outside exercise than the high group. This is a key finding.

When people train at a high intensity or for a long duration, they tend to be far less active outside their exercise session than those who train at a lower intensity or for a shorter duration. If a workout wipes you out for the rest of the day, you’re more prone to being sedentary the rest of the day than if your workout left you feeling invigorated.

Studies also show that when people feel they can eat anything they want following exercise, they eat more when they exercise more. That would also hold people back from losing weight, though diet was monitored in this study.

Another possible issue with the higher-intensity group could have been that they burned more energy from glucose than from fat. Their respiratory quotient, a measure of fat utilization, was not measured, or was not discussed in the paper, so it’s difficult to know if that could have played a part as well.


High-intensity, all-out-effort workouts are fun and useful on occasion, but you don’t need to have a calorie challenge with yourself every workout. One of the most common mistakes people make when they begin exercising for fat loss, is to do their cardio with as much intensity as they can for as long as they can stand it. Then they go home wiped out. You don’t need to do that for successful fat loss.

In fact, the best way to know how hard you should be training is to complete an exercise metabolic rate (or CardioPoint) test. You can then identify at what intensity you should train. From there, if you’d like to hop on a treadmill or go for a jog outside, keeping an eye on your heart rate. Periodization is key to long-term health and performance improvements. If you’re not sure how to structure your workout sessions for the best results, talk to a health and fitness professional.

Written by Tom Nikkola – Director of Nutrition & Weight Management

[i] Rosenkilde M, Auerbach P, Reichkendler MH, et al. Body fat loss and compensatory mechanisms in response to different doses of aerobic exercise – a randomized controlled trial in overweight sedentary males. Am J Physiol regul Integr Comp Physiol 2012;202:R571-R579

This article is not intended for the treatment or prevention of disease, nor as a substitute for medical treatment, nor as an alternative to medical advice. Use of recommendations in this and other articles is at the choice and risk of the reader.

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Reader Comments (6)

GREAT READ will def make sure all TEAM INSTRUCTORS send out to TEAM CLASSES

October 14, 2012 | Unregistered CommenterFREEMAN

I do not have access to the full study in the American Journal Of Physiology, but I was able to find the abstract that talks about some of the details that are not included in the article above. The sample size seems adequate for this initial study, but will require further research with a larger sample to understand the outcome further. There were only 61 participants divided relatively equally (18 control, 21 moderate, and 22 high) in this study over only 12 weeks, so there could be skewed numbers based on how the "moderately overweight young men" were selected (were any of them already working out? how were they found?), what time of year the study was conducted (being inside more during the winter could cause more sickness or seasonal allergies) and other factors.

With that said, I am neither a statistician nor a clinical trial expert, so take my comment with a grain of salt.

October 14, 2012 | Unregistered CommenterJEB

Really dissappointed in this article. It seems to contradict itself many times. After reading I am unclear which intensity is best. The evidence is vague in my opinion as well. I would love for this article to be expanded opun, or completely re-done, as is it is not worth sharing in my opinion.

October 15, 2012 | Unregistered CommenterHeidi

What really makes sense to me is to work out so strenuously that you become sedentary the rest of the day.Ive never thought about it that way and now that I do I believe this to be true.

October 16, 2012 | Unregistered Commenterjim

This study confirms my training experience years ago before HR monitors and VO2max were utilized. I trained 3x a week at high levels (over AT heart rate). Was not overweight and did not lose much weight (1-5 lbs.); ate whatever I wanted, but was "wiped out" on non- training days; spent much time "relaxing" when not working out. Since using a HR monitor and testing for cardiopoint, I find I can lose weight, have plenty of energy and increase my AT by closely following a structured HR focused workout. Interesting to learn I could have achieved same results years ago in less time and stress.

October 17, 2012 | Unregistered CommenterBwins

I agree with Heidi...very confusing article and full of contradictions. I too cannot tell which type of workout this article is recommending and why. It would really be nice to have some sort of an Editor review these articles before posting online...I just felt that I wasted my time reading it (and now commenting on it). If this happens few more times, I would be inclined to ignore this whole website, regardless of how enticing the article title is.

October 28, 2012 | Unregistered CommenterIJ

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