Muscle weighs more than fat - true or false?

what is the truth?
I am training fairly hard (for me anyway) esp on hills at mo and have been upping my core strength work with sit ups etc to help an injury issue. Not changed my diet, but have put on 5lbs. Is it a myth that muscle weighs more? I certainly don't feel like I've gained any weight.
Should I ditch the scales? Is their an ideal weight, or is it not important for an amateur runner? Should I work on measurements - or just go with feeling good?
Just interested on others thoughts


  • Yes muscle is more dense than fat, so its possible that you have gained 5lbs but still have the same waist measurement etc. I.e. you have more muscle and less fat than you did before.

    I feel for fit people its better to go by how you feel and by measurements rather than weight.

    P.S. I had to say 'dense' rather than 'weighs' otherwise someone  would have given me a lecture involving a ton of feathers and a ton of lead!

  • For the same volume muscle weighs more than fat but of course 1 lb of muscle weighs the same as 1 lb of fat.

    Re core exercises sit ups are a particularly ineffective way to strengthen the core and often make core strength worse not better
    Have a look at this blog for the reasons why

    Combination of scales , measurements and how you feel is the best way to see what your weight is doing. obviously the more weight you carry the worse it is for your running but unless you are elite carrying a few extra pds of muscle in your upper body isn't going to matter much
  • ton of feathers vs ton of lead. 1lb of muscle vs 1 lb of fat - why oh why has this become something that is quoted all the time - it's true but it has nothing to do with how much something weighs.

    If something is denser then it is heavier. If you have fallen for the '1lb = 1lb' statement then you need to understand what 'weight' is. There needs to be a volume specified - either explicit or implied. i.e. how much does that elephant weigh? (volume = entire elephant), no-one asks how much does 1lb of elephant weigh now do they? Another example - how much muscle weight are you carrying - the implied volume is all the muscle on your body. When someone asks is muscle heavier than fat - a fixed volume is already implied in the question - otherwise the question is meaningless. I realise this sounds a bit patronising (so sorry about that) but it's just something that seems to almost have become a meme the amount of times it is quoted on weight posts and it is just bonkers and irrelevant.

    Back to the OP.

    yes, muscle is heavier than fat. Whether or not your 5lbs is muscle though is another question altogether.

    Have your dimensions changed? That is the more important thing to be looking at. I would suggest that 5lbs of muscle would require a heck of a lot of work but it is very much body-type dependant. i.e. a male mesomorph will find it easier to put on muscle than a female ectomorph.

    You say you haven't changed your diet - unless you are scrupulously writing it all down then there is a good chance you are unconsciously eating more. The first year I trained properly I put on about the same (5-6lb) I would have swore blind I wasn't eating more but I was. On the upside I did get faster and stronger and a few diet tweaks got the weight back off again while the speed etc stayed.

    (edited to try and be more tactful - hope it worked)
  • Wow my plan to avoid getting a lecture backfired a bit!


  • Gymaddict is spot on image
  • ;) couldn't help myself.
  • Fat floats whereas muscle sinks as I recall - is not the proper way to get your body-fat calculated to get weighed underwater ?

  • PhilPubPhilPub ✭✭✭

    Spooky.  I was imagining the "muscle weighs more than fat" discussion on the way in to work this morning.  (OK, not spooky, probably just sad!) and wondering how long it would be before someone corrected someone who wasn't actually incorrect in the first place.  But gymaddict explained it better than I probably would have done.

    Actually if you wanted to be really anal, I'd prefer to define weight as "The force with which a body is attracted to Earth or another celestial body, equal to the product of the object's mass and the acceleration of gravity."  In other words, a body of a certain mass will weigh a different amount depending on the force of gravity.  On the moon, your mass is the same but you weigh less.  That doesn't tell us much about the muscle vs fat debate but there you go.  image

    Getting to the practical matter in hand, since body composition can change a fair bit given changes in exercise regime, diet, etc. I think the best thing is not to get too hung up on your weight as such but keep an eye on waist size and how much flab you can pinch around the belly.  And how you feel, how fast you're running, how you're sleeping, etc, etc...

    BTW that link from Andrew makes very interesting reading.  I may be making a few tweaks to my core exercise routine to make it a little more dynamic and running specific.  More twisting, less static.

  • Phil - As a former physicist I used to preface my explanations with a few disclaimers but it usually just made things more complicated. Most folks don't really want to differentiate between mass and weight and really aren't interested in the 'real' definition of weight.

    After all - we are all on the same planet and the variations in gravity aren't significant enough to bother about.
  • Gym addict wrote "If something is denser then it is heavier." No, it's heavier per unit volume. If I dropped a gold ring or a one tonne weight made of aluminium on your head (from the same height in the same gravitational field), you'd come off worse with the tonne weight because the less dense block of aluminium is heavier.

  • I guess for (us) scientists the weight of muscle vs fat issue is always going to be easy to understand - it's basic science taught at school (or was in my day - I have no idea what they teach now).

    but for non-scientists the old myth of muscle being heavier than fat is easily understood as they don't have the understanding of mass or density (or have forgotten it) - it's such a commonly used statement that you can understand why people believe it's true. sadly it's a commonly used statement in publications that really should know better as well - often those related to exercise or food and are trying to promote something!!!
  • You're all missing the point.

    The op wants reassurance that they haven't really failed at maintaining/losing fat because they've convinced themselves that they've gained muscle.

    Rather than arguing semantics over mass, you should be saying the op doesn't "feel" bigger because they've toned some underlying muscle through exercise, but have gained almost 5lb in fat through subconsciously eating more...

    Running and sit ups alone are hardly likely to gain you 5lb of pure, hard muscle...

    If you can be genuinely subjective about your body composition, then yes, ditch the scales. If however you (like me!) find it easy to convince yourself you're getting more stocky, gaining muscle in a good way, then no. Because before you know it, you'll go from 12.5st to 15st, and wonder why you've got slower!

  • Just work on measurements - from experience, when i was attending a gym 3 times a week I put on half a stone, but at the same time dropped a dress size from 14 to 12.

    Another example, based just on their weight and height, any rugby player would be considered Obese!

  • @lardarse - I did say all of that too image
  • Mmm, I think there is a great deal of mass vs weight confusion here, even from physicists.

    Gym addict is not entirely correct, just because something is denser doesn't mean it is heavier, how can it? If that was the case a small peice of mercury would for example have a greater mass then the Atlantic Ocean, because it is more dense

  • density is not the same as mass, it is defined as an objects mass per unit volume.

    therfore if you took the same volume of muscle and fat,  the muscle would weigh more.

  • I would be happy to say that mercury is heavier than water. The implication in that statement is that the volumes compared are the same.

    I don't think there is any confusion over weight and mass.

  • I like to think of it like this (keeping it simple as otherwise my head explodes).image

    A kilo is a kilo whether it is muscle or fat...however, a kilo of muscle will take up less space on your body than a kilo of fat, which is where using the tape measure rather than just the scale can help you work out what is going on.

     In my humble opinion it is quite difficult to gain significant amounts of muscle, in a shortish period of time, especially without doing targeted exercises (lifting weights/resistance) and by making certain changes to your diet. OP, you don't mention how long you've been training harder, but as long as you're feeling ok and have no specific body fat goals, you can still fit in your clothes and run within your own defined parameters, I probably wouldn't worry. If the upping of the training is recent, you might find you are retaining glycogen and water in your muscles to aid repair and that could be the gain showing on the scale. I find I easily retain 3-5 pounds when I first start to up my training, but that soon settles out as your muscles get used to the new regime.

  • PhilPubPhilPub ✭✭✭
    GymAddict wrote (see)

    I would be happy to say that mercury is heavier than water. The implication in that statement is that the volumes compared are the same.

    I don't understand why people don't get this.  In the statement "muscle weighs more than fat" is it not bloody obvious that the amounts of both substances we are comparing, as implied by the simplicity of the statement, is volume?  It is to me, which is why criticisms of the statement, or even worse positive statements of fact that it is in fact wrong, wind me up so much.

    Can we talk about iPods please?

  • "Another example, based just on their weight and height, any rugby player would be considered Obese!"

    oi - are you calling me obese?? morbidly obese please.... image

    what a great argument this is - basically all arguing the toss about the same thing but approaching it differently!
  • mmm I like my ipod. They are banned in triathlons though.....

    @Phil - with you on that - I keep thinking... any minute now the penny will drop.
  • well if the fat buddha name fits?. . . . . image

    seriously though, clearly they are not, but by a normal weight to height ratio it would appear as such on one of those simple BMI calculators that don't really tell the whole picture! 

    try putting in 18 stone and 6ft on this one and see what happens

    I can join you as well cos at 5'4", and a size 12, i am 11 stone - this means i am overweight. (mind you i only have to lose a couple of lb and i am 'normal' - whatever that means. . . . ) 

  • MM - why do you think I'm called FB?? ex-prop....

    my BMI is 34. 5 Ironmans and 21 marathons and still classed as morbidly obese. love it!
  • just looked at that Mile27 core exercise link - cool background, I have almost identical images in my holiday snaps!
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