Weight (fat) loss v increased muscle tone

[caro_]

Help - I am confused. Am training to do a 5 mile run and the fat is falling away nicely - not losing any weight though cos building up muscle.

I just wondered - as we are told one of the problems with being overweight is the strain on our heart, joints etc, how does the heart differentiate between fat and muscle when you are running, living etc.

Obviously you are fitter and so on, but is it that the muscles support your joints (as I suspect is the case) and also your heart?

Can someone with a more scientific mind than mine explain please.

[Loosehead]

Mostly it's body composition that matters, if you are heavy but lean then that's fine. The traditional BMI is pretty much discredited now, it's fat % that is considered more important.

Fat deposits are what cause a strain, ie a lot of dead weight stored around the the body fat in the arteries and fat deposited around the organs. Muscle is heavy yes but it forms part of the overall fitness equation. Muscle uses more calories at rest for example and although there is weight on the joints the muscle tends to support the joints if sufficiently developed also a health body will reinforce bomes and joints to take account of the increased loads being put on it.