Floating on the surface

[boulderjohn]

The BMI takes an established norm for the weight-height ratio and then assumes that any weight above that norm is fat.

The problem is that anyone who exercises enough to add any muscle mass above that norm (which was apparently determined by measuring anorexics) will have that additional muscle interpreted as fat. If you look at the height and weight of just about any NFL player, including the smaller, speedy running backs without a sign of fat on them, and you will find that they almost all obese according to the BMI.

A few years ago DAN made some statements related to diver fitness relate to BMI, and I challenged them on that. In response, they had a doctor research fitness measurement methods, and they published the results in Alert Diver. He determined that for individuals, the BMI was the least accurate way to estimate fitness and body composition.

A number of years ago, when I was more fit than I am now, I had a body fat test done using the process of measuring my weight in and out of water, which is considered the most accurate method. The analysis I received included an estimate not only of my current body fat percentage, but an estimate of what that percentage would be if I lost different amounts of weight, assuming all such weight loss would be attribute to fat loss. According to that analysis, for me to get out of the overweight category in the BMI, I would have to get my body fat down to exactly 0%.

 

[FPDocMatt]

I've seen published density figures for muscle varying from 1.04 to 1.2, for fat varying from 0.65 to 0.92 and bone anything up to 2.5 all in gm/cc.

From this I conclude that:

1. Other things being equal, a larger-boned person would be less buoyant.
2. Other things being equal, a person with a higher body fat percentage would be more buoyant.

#1 could be the explanation for a thin person being more buoyant than another thin person of equal weight. He is smaller-framed. (As a previous poster in this thread has already pointed out.)

It's probably not the most reliable method, but one way of measuring whether a person is big-boned or small-boned is to put the middle finger and thumb around the wrist. If the fingers overlap, you're small-boned. If they don't touch, you're large-boned. And if they just touch, you're average-boned.

Now, I'm thin but am small-boned. This might explain why I need more weight.

 

[The Chairman]

One factor Dopp alluded to was simple confidence in the water. The more you dive, the less you tend to over inhale. One of my favorite habits to help people break is taking a deep breath before they descend. That's the point you want to be densest, so learn to exhale to descend and peel off a bit of that lead as you master this.

As for being buoyant, I did the entire dive master treading water with out a single kick while holding my hands out of the water.

 

[boulderjohn]

And if I had been in the water with him at the time, I would have been so PO'd I would be shaking. I might have hit him. Just staying on top of the water was the hardest part of DM training for me.

 

[k ellis]

NetDoc I am envious of you because I did the divemaster float for 15 minutes with the last 2 minutes hands out of the water. I finaly gave up and put my hands down in frustration but only to find I had 2 minutes and 5 seconds out of the water I barely passed but I passed it

Cool thing about diving is you learn alot of things you take for granted even when swimming. You learn how your lungs play such a crucial role in obtaining neutral buoyancy and you learn how placing more air in your lungs will lift you up effortlessly over anything you want to go over. Then you also learn breathing smaller breathes will send you back down.

 

[TSandM]

I'm another one of those people who did the DM float without kicking.

But before you get mad at me, realize I carry six to ten pounds more lead than anybody I know. The DM test was one night, but the 6 to 10 lbs is forever

 

[Hawkwood]

And if I had been in the water with him at the time, I would have been so PO'd I would be shaking. I might have hit him. Just staying on top of the water was the hardest part of DM training for me.

I had to laugh at this. Hands out for the last couple of minutes was the hardest thing I had to do. in the pool, I sink when wearing a 3mm.

 

[The Chairman]

I had to laugh at this.

I have to admit laughing at the poor schlep next to me struggling to stay afloat. We know him as Moose on this Board! But heck, what are best friends for?

 

[Leynabelle]

Hi, I'm very new to the forum and just started browsing looking for advice on bouyancy - this thread is somewhat helpful in answering my question: do I have trouble descending because I am so fat? I'm 5'4", and when I first started diving (1995) I weighed in at a whopping 100 pounds. I didn't have any trouble descending. Then, after 35, my metabolism changed dramatically. Without any other lifestyle changes, I went from 100 pounds to 145. Ick!!! I went diving in Cozumel and Maui last year, and even with 15 pounds of weight on I had to pull myself down the bouy anchor - anything less than about 10 feet and I popped up like a cork. I'm trying to lose some of the weight (which is REALLY hard when you're almost 50 and have been skinny all your life!!), but until I do how do I descend without burning half my tank fighting to get down? Help! I'm diving in Roatan in early May and would like to be able to stay down more than 45 minutes :cool2:

 

[The Chairman]

You'll have to simply add more weight in the interim. Don't overdo it, but try it at 20 pounds.