Long, Slow Cardio: Another Dagger to the Heart?

Several weeks ago, a few of my clients and colleagues were kind enough to forward me a story written by Dr. Johnny Bowden for the Huffington post entitled “Exercise: The News You Don’t Want To Hear“.

In his article, Bowden concluded that exercise, by itself, results in a fairly disappointing amount of weight loss.

Obviously, there are countless other impressive health and well-being benefits that come from regular exercise, but magical fat loss just isn’t one of them – a point I’ve stressed in a number of blog posts I’ve published in the past.

Reading that article reminded me that I still needed to put together my commentary on a recent study on exercise duration and body weight loss published by a group in Denmark: Body fat loss and compensatory mechanisms in response to different doses of aerobic exercise – a randomized controlled trial in overweight sedentary males.

This particular article is open access, and I encourage everyone to download a copy and read it for themselves.

For people who don’t love reading original exercise science articles themselves (and seriously, who doesn’t???), allow me to summarize this study quickly.

The researchers in this study wanted to determine the impact of exercise duration on resting metabolim, appetite and ultimately weight loss. Two groups of young men were instructed to perform daily aerobic exercise for 13 weeks, using either a treadmill or stationary bike.

The major difference was the calorie-expenditure goal for each group. The targets were:

  • group one: 300 kcal/day (~ 30 minutes of exercise)
  • group two: 600 kcal/day (~60 minutes of exercise)

Before I get to the results, I want to send my cudos to these researchers. After reading through their methods, I was blown away by the lengths they went to in an attempt to quantify and control their subjects behaviours.

Not only did they track energy expenditure/heart rate during each bout of exercise, they used accelerometers to track weekly lifestyle physical activity in two separate weeks (week 6 and 11), and also routinely check-in with their subjects to ensure they were actively following the workout prescription.

This level of physical activity tracking in an of itself would make it a much better designed exercise study than most that get published, but these researchers were also interested in intake and appetite measures, so they measured that too.

Actually, the researchers didn’t just track intake, they actually provided all their participants with two 8 day periods worth of food (8 days before the exercise intervention started and another 8 day period after the 13 weeks were up).

By providing their subjects with all the food they would need for the week (and collecting any food that was uneaten), the researchers were able to have a fairly precise idea of just how much food was eaten.

Quality research design brings a tear to this exercise nutritionist’s eye…

I cannot stress enough how much better this approach is compared to asking people to fill out food logs or making up bogus egg consumption questionnaires

I could go on and on about how well controlled the researchers attempted to make this study, but I think you get the idea.

Now onto the results!

The Big Reveal

After 13 weeks, the group that exercised for 60 minutes a day lost, on average, 3.8 kg of fat… or about 2/3 of a lbs of fat per week.

If you’ve followed any of the literature on aerobic exercise as a weight loss tool, that number sounds about right. It actually probably is even a little better than what most people could expect, considering this was a group of young males, and young males are the most responsive members of society to any weight loss intervention.

But I think we can all agree, this particular finding doesn’t add much to the field of weight loss.

What does rock the boat was the fact these researchers found that the group that did only 30 minutes of exercise a day lost, on average, 4.0 kg of fat.

Yup, you are reading that correctly.

In this study, it would appear that doubling workout time (from 30 –> 60 minutes) made NO DIFFERENCE in how much fat these individuals lost from exercise!

30 minutes of aerobic exercise was as effective as 60 minutes of aerobic exercise, from a fat loss perspective

This my friends, is a result worth publishing.

Mind you, at this point in time we can’t say with 100% why the group that only did 30 minutes of exercise lost as much fat as the group that did twice as much exercise.

On some level, the group doing twice as much exercise had to either a) eat more than the group doing 30 minutes or b) burn less energy outside of their structured periods of physical activity.

Unfortunately, the measurement tools used in this study weren’t sensitive enough to explain their results. Despite the best efforts by the research team to track outside the lab behaviour, it’s simply impossible to monitor exactly what humans do 24/7.

Regardless of “why this happened” though, the end result is the end result.

In other words, a take home message for exercise as a weight-loss tool might be:

  • Exercise alone won’t make you lean…
  • But some exercise will help you drop a bit extra fat…
  • Exercise is really important for protecting lean mass…
  • But there is certainly a case of diminishing returns

In other words, don’t fall into the trap of thinking more = better. Better is better.

Incidentally, the results of this study do partially support my theory of why shorter/more intense training leads to better body composition change long term. Not because of any “metabolic afterburn”… but mostly because you don’t expend enough calories while you are doing it to significantly increase appetite.

Several other researchers, notably Barry Braun, are arguing their may be a threshold of energy-expenditure from exercise that once surpassed, tends to spike appetite. I tend to agree.

Again, I do want to highlight this is only one study (and doesn’t “prove” anything), but hopefully it does cause you to rethink your own approach to working out, particularly if you aren’t getting the gains you think you should be.

If you are someone who has the physical structure to deal with hours and hours of cardio and who enjoys it – by all means keep doing so.

For everyone else simply seeking to look and feel better, keeping your cardio sessions to 30 minutes might be all that you need to optimum results!

Would love to hear whether you agree or disagree with what these researchers found – leave your comments below.

Till next time, train hard and eat clean!