less muscle, less fluids?

vio765 said:

i am a serious Cat 4/5 racer losing serious weight. before cycling i lifted a lot and therefore had a lot of muscle weight. i weighed 175 about 2 months ago and now im at 157. and yes, to the pain of many ears, it has been through the low-carb dieting. im estimating that 2/3 of my weight loss came from fat and the other 1/3 from muscle. i still have about 8-10 more pounds to go, and i think i can lose that by x-mas. i have been staying on the bike so that i would lose the least amount of muscle from my legs and back while "thinning out" my arms, chest, and back. it has worked. I know i have not lost any significant power (i have a powertap) becuase i took a couple days off from the diet and found my performance was very close to where it was before i started dieting.
SO! my questions is that when all of this is done, i will have little fat (acting as insulation) and only cycling-critical muscle. does this mean i wont need to drink as much?

How tall are you?

vio765 said:

does this mean i wont need to drink as much?

No. You might even need to drink more, because in addition to losing fat and muscle, you are losing your body's ability to store water and electrolytes. The effect of fat on "insulation", unless you are swimming, is small compared to the excess heat generation from exercise. Air is not a good conductor of heat. Water is, which is why swimming is different.

i am 5' 8.5" i figured that the more fat, the more insulation, and therefore i would need to cool my core more. so the leanest of cyclists would sweat the least because they have less insulation. my logic.

vio765 said:

i am 5' 8.5" i figured that the more fat, the more insulation, and therefore i would need to cool my core more. so the leanest of cyclists would sweat the least because they have less insulation. my logic.

That might be true if you were comparing a lean cyclist to a morbidly obese cyclist, but at 5'8.5", the difference between 175 pounds and 157 pounds will have a negligable effect on insulation. When you are down to that level, you are no longer talking about substantial differences in subcutaneous fat. The difference is in muscle mass, muscle glycogen, and abdominal fat.

If you were lifting weights before, my guess is that much of the weight you have lost is muscle and glycogen. Some loss might have been abdominal fat, but it is unlikely you have lost a significant amount of subcutaneous fat. The other thing you have lost with the weight loss, regardless of whether it was muscle, glycogen, or fat, is the ability to store water. Thus, while at 175 pounds, you could probably lose 5.25 pounds (2.4 liters) of water without having a major impact on your performance. At 157 pounds, an equivalent weight loss would be 4.7 pounds (2.1 liters). That means you have 300 mL (about 10 fl oz) less reserve water in your body at the start. Also, since you are losing what you consider to be "non-essential" muscle as far as cycling is concerned, where the body is going to start robbing muscle is the intercostal muscles (those responsible for breathing) and the legs.

The bottom line is that the role of subcutaneous fat in insullation, except in swimming and in the morbidly obese, is negligable. In losing weight, the power to weight ratio might have shifted more to your favor, but the weight loss will not mean you can drink less, and it could mean that you need to drink more.