Friday, August 26, 2011

low-intensity cardio or high-intensity strength training?

I love it when I figure something out on my own, and then I read that same thing later from a professional; I guess it makes me feel smart.  Also it validates my belief that logical reasoning is a legitimate way to discover new truths.  There's a debate in exercise science over the best way to lose weight.  The conventional theory was that long, low-intensity cardiovascular exercise like running or cycling would be most effective, because when you run slower, your body gets a higher proportion of that energy from fat than from carbohydrates.  Recently people have challenged that by saying that high-intensity strength training like P90x actually works better, because when you workout at high intensity you burn more total calories.

I thought about this a lot, because both sides have a good argument.  I have been especially troubled by hearing more and more anecdotal evidence of people saying that they tried jogging and it didn't help, but then they tried weight lifting and they lost big-time.  But one day it just clicked!  Per calorie of work done, lower intensity is more effective at burning fat; however if the high-intensity workout uses way more total calories, that lower ratio of fat/carbs burned will not make enough of a difference to tip the scales.  This might be more clear with some numbers: 30 minutes of jogging at 80 calories per ten minutes is 240 calories.  But if you do 20 minutes of max-interval cardio where you are burning 150 calories per ten minutes, you will go through 300 calories.  But the ratio of calories of fat to calories of carbs might be 70/30 in the first case, and 50/50 in the second.  And 70 percent of 200 is 140 calories, but 50 percent of 300 calories is 150 calories!  You worked out a third less time doing the high-intensity stuff, and the ratio of fat burned was lower, but the intensity was so much higher that you still burned more fat lifting weights.

I think what is really happening is that people are doing long, high intensity workouts, compared to short low-intensity workouts.  In this case, clearly they are going to drop more weight in the first case.  So what does this say about the debate?  Who was right?  Both sides are-they were just making different claims.  Per calorie, lower intensity is more efficient at burning fat.  But high-intensity has a greater capacity to burn more total energy, so in some instances, it is better at helping you trim down.

My theory was confirmed the other day when I was reading Trailrunner Magazine (motto, "one dirty magazine.")  They had an article about whether or not running was an effective method for weight loss, and remarkably, their overall conclusion was no.  They mentioned this ratio/intensity issue that I outlined above, which is where I got my vindication.  An interesting observation they made was that even though running is the highest calorie burner of any aerobic exercise, you only burn a lot of total calories if you can run a long distance and a high-intensity.  The problem is that people who are overweight or otherwise in poor health can't do that.  Elite runners can, but they are already so thin that weight-loss isn't an issue.  Running fast makes you thin, but you have to be thin to run fast; it's a bizarre catch-22.

The Trailrunner article got it's main conclusion from a study where one group changed their diet, and another group changed their diet and added running to their exercise; the second group lost only slightly more weight on average.  I read about another study on Joe Friel's blog where they had one group lose weight by eating less, and another group lose weight by exercising more.  The group that ate less lost more weight then the group that exercised more, but the second group lost more weight from muscle then did the first group.  So all of this tells us two things; if you want to drop a lot of weight fast, change your diet.  But if you are an athlete that wants to maintain muscle mass, exercising more is slower, but might be better for your overall fitness in the long run.

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