Answer: Lose Weight or Train? Power Increase Explained

[Byrne]

EDIT -- I posted this here because I figured its more of a conceptual problem than a HW problem, but if people see otherwise, feel free to delete the post.

I'm having troubles wrapping my head around this one (I've provided the example from my class notes below):

Q: Is it better to lose 5 kg of body mass (assume no change in muscle strength) or to train harder and gain 15 W of power?

Given:
75 kg rider producing 250 W of power

ANSWER:

75 kg / 70 kg = 1.071
In terms of Watts: 250 W x 1.071 = 268 W, ~ 18 W increase

So, depending on the initial weight, the athlete might see as large a benefit from losing weight as training harder.

My question -- how does a decrease in the mass of the rider increase his power producing ability by 18 W? Intuitively, I would think that a rider with lower mass will experience less resistive forces when riding (i.e., gravity when on an incline, kinetic friction) and so can sustain the same velocity as a heavier rider without applying as much force and, therefore, less power.

From a physics standpoint, how does a mass decrease result in an increase in Power as this example suggests (taken from my class notes)?

Thanks!

 

[rcgldr]

"Rider"? Climber would be a better description, the riders weight is being treated as the opposing force in this problem.

 

[sganesh88]

I don't think our bodies are that simple to derive power from the ratio of masses. It seems ridiculous. Even this 250 watt cannot be sustained forever. A cheetah-at it's max speed- should stop pursuing the deer within 40 seconds or so before it gets hyperthermia. :)