Body weight and power?

terry potter

I am interested to find out the relationship between power output and body weight. I am 178 lbs and I am curious to know how it would effect my cycling if I was to drop 10lbs. I have never cycled at that weight. My riding is mixed 80% flat 20% hills, this is during a 3hour 100km club ride.
Cheers Terry.

INCE

As long as you don't lose too much muscle mass, your total wattage generally should not decrease. Keep in mind that certain percentage of your total weight lost is ALWAYS some muscles mass (unless you have some metabolic disorder). .

There is a finite limit however.

I found that if I monitor % body fat (taking care not dropping below certain, found through trial and error, age-adjusted minimum), the total wattage may even increase.

The overall effect on W/kg (of dropping unnecessary weight) is very drastic. Weight reduction is literally more effective than any doping. By my estimate, to a point of course, each 1% of body weight lost translates to 1.5-2% increase in W/kg. I suspect it's due to increase in efficiency associated with loss of live biomass that requires more maintenance energy than the equivalent static weight. Cheers.

daveryanwyoming

On long or steep hills the savings is almost directly proportional to body weight assuming your power stays the same. Climb a long 6% grade and drop those 10 pounds (say 198 total with bike to 188 total with bike) and you'll get up that hill about 5% faster for the same effort. Or you'll climb it at the same speed but it won't feel so tough.

You save a bit on flats, but much less just some due to decreased rolling resistance and generally lighter folks punch a bit smaller hole in the air so perhaps a bit of air resistance. But the big savings happens while climbing. If you want to do some "what if" planning check out: http://www.analyticcycling.com/ForcesSpeed_Page.html and plug in different weights for the same power at various grades to see the effect of weight(enter total weight of you, the bike, your water, etc.).

Anyway, watts per kilogram is what it's all about for hills at least. Ideally you increase watts through training and decrease kilograms to a healthy minimum. But even just working the kg side has benefits. You might also be interested in Andy Coggan's power profiling: http://www.cyclingpeakssoftware.com...rprofile_v4.gif
Enter an estimate of your power for various time durations at various weights and see where that places you on the profiles.

If you'll still be healthy at the lower weight, then by all means drop the pounds.

-Dave

Steve_B

No, the effect upon W/kg is due to Watts and due to kilograms, nothing more, nothing less. It's pure physics. For the same power going up a hill, the heavier rider will be slower.

When I go to analyticcycling.com's Forces On A Rider section, I don't see a place to enter "% live biomass".... Think about why that is.

kmavm

Nobody's denying that; however, my experience has been that losing weight can, directly or indirectly, raise the W numerator as well. Speculating that it's due to your heart and lungs having a lower resting metabolic rate, and therefore can divert a greater portion of your limited VO2Max to working musculature.

daveryanwyoming

Same experience here, but I strongly suspect that's because I lose weight by increasing exercise not by strict dieting. IOW, my weight loss comes from more time on the bike, not surprising power increases are correlated with weight losses when those weight losses are driven by exercise.

-Dave

Steve_B

I don't know. According to this adipose tissue contains many small blood vessels, but is it drawing away a significant amount of resources during exercise?

kmavm

True, but a) every little bit counts, and b) who said you're only losing fat? If my speculation has any truth to it, losing non-cycling muscle (i.e., upper body) would be the most valuable weight to lose of all...

Squint

Could it be that when you're leaner, your body dissipates heat better?