Help me, O Exercise Gurus.

July 3, 2009 1:26 AM

Burning calories while exercising: how important is how much effort you put into it? Does difficulty enter the equation, or is it all time and distance?

Here's an example of what I mean: I've been riding my single gear bike to and from work for the past month on a route that is rolling hills that go as high as a 7% incline. It takes me about 40 minutes to get 5 miles, and I'm huffing and puffing for most of the trek. A few hours later, after standing on my feet all day, I turn around and bike home, which takes me roughly an hour. As I get more used to the ride and it becomes easier, does the amount of calories I burn drop, since my heart rate is no longer skyrocketing, or does it go up, since I'm going faster?

What counts as "moderate" exercise? Does all my heart-pounding biking count as "leisure," since I'm only going a total of 10 miles? Do calorie calculators take effort into consideration, or is "difficultly" measured by how fast you go in a certain amount of time, regardless of your heart rate?

posted by canadia to health & fitness (10 answers total)

There's two things going on here. The amount of calories you burn performing the activity, and the increased energy consumption (often referred to as 'afterburn') that goes on after exercise where your metabolism is raised for a period after the exercise. Afterburn includes repair to the muscle tissue you've damaged during exercise and increased with intensity.

Most calorie counters will tell you X calories for X distance of activity. In a ballpark way, this is generally true - eg it takes approximately 1000 calories for a 130 pound person to run 10 miles regardless of pace. But, in my (and many others) experience as an elite runner it's not so simple. I always noticed a big drop in weight the fitter I got, particularly during periods of running intense intervals on the track. I attribute this to several factors:

- being fit allows you to do a greater volume of work, thus able to burn more calories easier.
- running fast creates much more damage and required regeneration than running slowly.
- intense exercise builds muscle which increases your metabolism.
- intense exercise increases levels of stress hormones, which also raise your metabolism and burn calories well after the exercise.

To answer the question, then, generally as you get fitter the energy required to perform your ride won't change. What will change in the absence of new stimulus is the afterburn effect where you're tearing your body down and rebuilding. As you get fitter, the less of this there will be.
posted by jimmythefish at 1:47 AM on July 3, 2009 [3 favorites]

The more you train, the more efficient you will become. You will burn fewer calories for the same amount of work.
posted by devnull at 1:50 AM on July 3, 2009

PS - moderate generally refers to the intensity of effort rather than the duration, though duration can have an impact. If you were to continue your 'moderate' 10 mile bike ride pace out to 30 miles, your heart rate would slowly drift upwards and what was once moderate would become a more difficult intensity. If you go by heart rate, you're not far off in measuring intensity.
posted by jimmythefish at 1:51 AM on July 3, 2009

jimmythefish: So is the afterburn what contributes to weight loss? And once you no longer have afterburn, your body is no longer burning those calories?
posted by canadia at 2:00 AM on July 3, 2009

In terms of defining "moderate" you might want to consider this in terms of heart rate training zones (calculated relative to your maximum heart rate).

If you loose weight over time then this will reduce the number of calories that you will burn for a given trip at a given speed.
posted by rongorongo at 2:13 AM on July 3, 2009

Both things contribute to weight loss - calories burned doing anything contribute to weight loss. It's not an easy or simple matter, though. As you get fitter and more efficient, if you maintain your same task at the same speed your 'afterburn calories' will drop off, yes. But, you'll be burning more at rest because of the increased muscle mass you've achieved. Don't ask me to quantify that, though! At the same time, as that intensity of effort decreases due to increased fitness, you tend to get better at using fat as an energy source as opposed to blood sugar (glycogen) which is used at higher intensities.

Generally speaking, I find that people will default to a given effort rather than a given pace - so getting fitter generally means eventually going faster as opposed to making things easier. On a fixie this has limitations, though. It gets uncomfortable to pedal really fast. In the absence of new stimulus chances are your fitness will plateau.

Weight loss is calories in vs calories out, ultimately, so you will require a calorie deficit to lose weight. This usually sparks a whole 'nother thing on Metafilter, so I won't get into it. But if your goal is to lose weight, you really just need to either do more on the bike (you'll know what that is when you get into it) and/or eat less.
posted by jimmythefish at 2:19 AM on July 3, 2009 [1 favorite]

On a bike, there are some tricks for burning more calories:

Go in a lower gear. For a fixie, switch to a smaller chainring and/or a larger cog. This gives you more power, but uses more energy (get "clipless" shoes that attach mechanically to your pedals and you will be able to go in a lower gear without your feet flying off the pedals from the speed of rotation).

Use a longer crank-arm, your leg moves further for each rotation this way.

Accelerate more swiftly - working your way up to speed slowly conserves energy. This works well in tandem with the gearing advice above.

Come to a full stop, rather than slowing to a yield at stop signs and lights, coming back up to speed will take more energy this way, and on a fixie coming to a full stop also takes more energy.

Basically play like you are a fast little sports car, spinning your engine fast, screeching to a halt, and then zooming off again (or your best imitation on a bicycle of this).

Move faster - get a speedometer ("cyclecomputer") for your bike, go two blocks at 10mph then go two blocks at 25mph, each on a straightaway, and you will see that it takes more energy to maintain a higher speed. With a speedometer, you can track your peak and average speeds, set long term goals for slowly increasing these numbers. Eddie Merckx, the greatest racer of all time, reportedly had the following mantra: "it never gets any easier, you just go faster".

Ride in an upright position - the more upright you are, the more you have to fight the wind in order to maintain speed.

Get a heavier bicycle, or carry a heavier load.

Put larger, knobbier tires on your wheels.

You will know you are burning more calories because you will be more tired afterward, and your appetite will increase (of course there is a red queen effect where you need to push harder to get that level of tiredness - see the Merckx quote above).
posted by idiopath at 3:06 AM on July 3, 2009 [2 favorites]

If calorie burn and fitness are what you are looking for, I think switching to a multi-geared bike is better.

First, it is harder to build "base" cardiovascular fitness on a fixed-gear bike because the key is to maintain your heart rate in the optimal "target zone" where you will be getting the best workout. Strangely enough, that rate is not near the maximum, but requires somewhat of a slower pace that that (I once did all the tests to find out my max heartrate and when I ran with a heartrate monitor after that it, I hated running in my aerobic target zone because I felt it was too slow.)

Second, once you have a strong base, you'll want to do intervals, described above. That will really build you up fast.

Essentially, you are just doing intervals now, which helps, but it is better to build base first.

Fixed-gear bikes are velodrome bikes, used in track racing where a more or less uniform effort will be used in the race or time trial. Because there is no need for shifting in such a situation, dropping the derailluers from the bike saves weight and let's you go faster.

In the end, using a fixed gear bike will result in some calorie drop per unit of time exercise because of the red queen effect above and because it will be harder to increase resistance. If that's really important, then get a multi-geared bike.
posted by Ironmouth at 4:02 AM on July 3, 2009

I wouldn't put too much stock into the so-called afterburn effect.

It's been studied in the past and more recently, and there's just very little evidence that exercise boosts the body’s ability to burn fat for as long as 24 hours after a workout.

A lot of people believe it does, so they eat whatever they want after a workout and make no (or very little) progress re: weight loss.
posted by foooooogasm at 6:47 AM on July 3, 2009

Thanks, everyone!
posted by canadia at 9:30 AM on July 3, 2009