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!