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Monday, December 21, 2009

Run, Fatboy, Run! Weight and Performance

How much is 20 pounds?

The other day I was at the store and picked up a 20lb bag of road salt. Oh. My. God. I can't imagine running with that extra weight, it's staggering. How did my knees handle the pounding? Next time you see one of those big bags give it a try... really drives home how much of an impact it should really have!

I remember showing up for my first 1/2 marathon in Peterborough.

I looked around and realized "I don't look like these people"! They were thin and athletic, I was close to 200lbs with a pretty respectable gut on me. I ran my little (big?) heart out to a 2:07 finish, side by side with some of the skinies.

The Performance Penalty

But what is the true penalty of extra weight? How much faster would my debut have been with the same training but 20lbs less to lug around?

Well first let's just look at the calories:

Calories (kCal) = 0.406 * (weight in pounds) * (distance in kilometers)

So plugging in the numbers for a 1/2 marathon, we get:

180 pound runner = 1542 kCal
200 pound runner = 1713 kCal

So it's just under 200 kCal difference. Doesn't sound like much, but it means running out of glycogen stores earlier or (more sensibly) having to knock back some pace.

Slow down, Fatboy!

Runner's World examined the issue in this article. Their conclusions was that all other things being equal, "healthy runners will race about two seconds per mile faster for every pound they lose". For a half marathon, they have a 20 pound reduction translating to slicing a staggering 8:44 off your time.

Almost nine minutes! Wow.

I recently did a half marathon in 1:47:43, at about 185 pounds. My goal is to get my weight under 170, which wouldn't quite be a drop of 20 pounds, but close... maybe I have a 1:40 in me yet!

Implications for biking and swimming

For both, the answer is "it depends".

Swimming - Fat floats... 'nuff said! Well not quite - you are punching a larger hole in the water which must use more energy. But on the other hand, I saw a program once on a gentleman attempting to swim across the English Channel, he intentionally gained massive amounts of fat to help him achieve the task (some of that may have been to tackle the cold, though!).

Cycling - I played around with this calculator a little. Being heavy increases rolling resistance, but relatively insignificantly. It would also increase your aerodynamic profile, but again this effect would be relatively minor for only 20 pounds. That leaves the biggest impact being dragging those big fat cells up hills! The amount of force that takes goes up pretty much linearly with weight... so either drop some pounds or ride flat courses.

Weight Loss = Magic Bullet?

No... remember the term "all things being equal". A heavy but fit guy can beat a light but unfit guy. But if you train the same amount, being lighter can shave precious minutes off your time, it's great bang for your buck!


answerphoned1,d6 said...

Interesting...what about the whole fat vs. muscle problem?

I assume as you become a stronger runner/swimmer/cyclist you may gain muscle. But does more muscle help athletes who are competing in short distances more than endurance athletes?

Double Bellybuster said...

You'll get your 1:40:00 this year. Having run a 45 minute 10K, and with your determination, this is in your near future for sure.

Jon P said...
This comment has been removed by the author.
Jon P said...

@Michael - I'm sure there are some muscle mass gains, but they're not enormous in endurance training.

Lance Armstrong

Fastest marathoners:

Ironman World Champion Craig Alexander

Nice strong go all day lean muscles! As you said, short distance athletes have the big muscle mass. Sprinters, track cyclists (or sprint specialists), and Michael Phelps swimmers.

I'm a looooong way from getting my fat down to the point where muscle is the only kind of weight I have to lose. :)

runwuf said...

"A heavy but fit guy can beat a light but unfit guy." - yes I heard you, this is what you kept on doing to me! :-)