Does losing weight increase fitness, beyond the obvious?

fergalr

Hi all,

I'm not sure where the correct forum for this is.
I do a few different sports. I've recently lost a few kgs.
So, I was wondering, when you lose weight, do you get fitter - specifically, does your aerobic performance increase, more than by the proportion you lost weight by?

In other words, does a leaner body perform better aerobically, separately from the fact that it's lighter?
(Ie if I lose 5kg and do a given aerobic task (eg running), carrying a 5kg pack, should I expect to see an improvement in times over before when I lost weight? (Neglecting issues like the pack bouncing and so on)).

Obviously shedding 5kg makes you faster, because you have the same muscles and aerobic system moving less weight around - what I'm interested in is whether your muscles and/or aerobic system also function better because you have less weight in your body?
(If this seems impossible, well, one hypothetical reason might be because the fatty cells consume less oxygen, not just to move them around, but also just to exist? But I suspect this is negligible in real world scenarios?)


Sorry to labour the point but I don't want to recieve replies along the lines of 'lighter people run faster' etc
You can assume it was fat storage that made up the lost weight, not a reduction in lean muscle.

I tried looking this up, but lack the biology knowledge to even start to properly find an answer...
I'd be grateful for answers and explanations - I considered putting it in the biology forum, but here seems more appropriate?

Boston

Well it would depend on how you loose the weight. If you're loosing weight or even maintaining weight and doing aerobic exercises, you will improve. You'd need to be doing aerobic exercises for about 4 - 5 weeks to loose 5Kg and its logical that your performance would improve if you've been doing something that long.

bwardrop

The answer is yes.

Don't have much time so I'll keep it quick. Your fitness is measured by your VO2max - this is the greatest amount of oxygen you can take from the air and deliver to your working muscles. It is measured in ml/kg/min - mls of oxygen per kilo of body weight per minute - it is relative to body weight.

If you lost weight without training - say simply through diet, but no extra exercise you will get fitter. Example:

Pre-diet - weight = 100kgs, absolute VO2max = 5000mls/min, therefore relative VO2max = 50ml/kg/min

Post diet - weight = 95kgs, absolute VO2max = 5000mls/min, therefore new relative VO2max = 52.6ml/kg/min

If you lost weight with training incorporated, you would have the above effect, plus all the physiological adaptations which will raise fitness / improve efficiency further. These adaptations, which I think you are interested in, will not happen simply because you have lost weight. There has to be a training stimulus for the adaptations to occur.

Fat cells are metabolically inactive and do not consume oxygen.

fergalr

The answer is yes.

Don't have much time so I'll keep it quick. Your fitness is measured by your VO2max - this is the greatest amount of oxygen you can take from the air and deliver to your working muscles. It is measured in ml/kg/min - mls of oxygen per kilo of body weight per minute - it is relative to body weight.

If you lost weight without training - say simply through diet, but no extra exercise you will get fitter. Example:

Pre-diet - weight = 100kgs, absolute VO2max = 5000mls/min, therefore relative VO2max = 50ml/kg/min

Post diet - weight = 95kgs, absolute VO2max = 5000mls/min, therefore new relative VO2max = 52.6ml/kg/min

I'm not really interested in relative VO2 max - as you pointed out, that obviously increases when you drop weight, as it's relative to your weight.
I am concerned about whether aerobic capacity will increase, independent of this weight lose.

Perhaps a better way of asking the question might be, will absolute VO2max capacity increase with weight loss? (Assuming that the process by which the weight is lost doesn't involve additional training which increases fitness... ie, you don't lose the weight by running an extra 5km a day or something)

If you lost weight with training incorporated, you would have the above effect, plus all the physiological adaptations which will raise fitness / improve efficiency further. These adaptations, which I think you are interested in, will not happen simply because you have lost weight. There has to be a training stimulus for the adaptations to occur.
Fat cells are metabolically inactive and do not consume oxygen.

Ok, this is indeed closer to what I was asking - you are saying therefore, that the answer to my question (or at least the question I was trying to ask!) is in fact 'No'?

fergalr

Well it would depend on how you loose the weight. If you're loosing weight or even maintaining weight and doing aerobic exercises, you will improve. You'd need to be doing aerobic exercises for about 4 - 5 weeks to loose 5Kg and its logical that your performance would improve if you've been doing something that long.

Boston, thanks for your reply - I'm not sure my question really came across correctly though... For arguments sake, lets say the weight was lost due to diet changing, rather than training level (and lets say the training level was already at an equilibrium point in terms of fitness gains, hypothetically).
My question was whether the fitness would increase, in absolute terms, just because of the weight loss. (Neglecting the increase in performance simply due to having to carry less weight - instead considering any possible aerobic adaptation that may occur simply because the body has less fat in it).

cowzerp

it would not just increase due to weight loss, life might be easier or sports due to carrying less weight but your heart and lungs will be the same unless you made them stronger, so your answer is no.

bwardrop

Absolute VO2 will not change due to weight loss, nor will it significantly change following training. There are a number of other cardiovascular functions that can improve which will result in fitness gains. There will be no aerobic adaptation simply because there is less fat in the body.

For the average Joe who has never really trained before, a fitness training program could be expected to improve their fitness by 10 - 20% (depending on their genetic potential). After this improvements will come in the form of improved efficiency without a significant increase in actual fitness levels.

Boston

No, I don't see how it would. Though I'm open to correction.