I’m aware of the difference in weight per cubic inch between fat and muscle, but is all muscle equal?
Is a well trained muscle heavier than an untrained muscle of the same dimensions?
Is fast twitch muscle heavier than slow twitch muscle?
This probably won’t help and it’s just an observation I had some years ago in the pool. That said it does ring a bell to me so maybe just add this into the highly unscientific pile of anecdotal info from the innerwebs. I had more or less this same conversation/question with my coach about 4-5 years ago when he was trying to help me grasp getting my body position sharpened up. I was convinced ‘density’ fit into that equation somewhere as to why I just wasn’t getting it. He then pointed to one of the university kids who was a blazingly fast fly/free sprinter. Guy was about 6’, 200 with quads the size of fire hydrants. He was cooling down with no kick at all, butt and hips out of the water, feet on surface just flopping along. ‘So you are taller and 20 pounds less with a longer torso and shorter skinnier legs…questions? It ain’t your body’s fault, it’s your ability to support yourself!’. Not to mention I probably had body fat at least 2x what his was…and if I had to guess based off a life of sport experiences I’m much more of a fast twitch guy than slow.
Hope that helps maybe…thought provoking? I’m sure we have some smarter people here on ST who will have the exact answer you are looking for. I’m just a big dumb animal this is as far as my pocket protector goes into the details;) If I’d of been paying attention more in college I’d of asked intently the how’s and why’s when I had hydrostatic tub body fat testing done. There has to be someone on ST who does this kind of testing I’d be shocked if we didn’t!
My colleague just published this: http://www.ncbi.nlm.nih.gov/pubmed/26156300
I haven’t read it, so I’m not sure if it directly addresses your question but you might find some useful references therein.
There’s also the consideration of glycogen content, which will also affect water content, which might affect density.
Finally, you might try looking at the articles found here: +AND+%22density%22+NOT+%22bone+density%22"]http://www.ncbi.nlm.nih.gov/pubmed/?term=“muscle%2C+skeletal”+AND+“density”+NOT+“bone+density”
Thanks for the links.