Aerodynamics / Aerodynamic Cost / Aero parts

Here's another one: lose 5kg of fat or gain 5kg of muscle? Light weight isn't everything.

It's not as cut n dried as that really, most muscular exercise training will result in an increase in lean muscle mass whilst you lose fat.
Clearly with some people they don't see a huge difference on the scales, but the %of BF goes down and obviously the benefit of increased muscle is that you can use it to push the pedals around.