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Waterdog7946
September 14th, 2011, 10:40 AM
Just out of curiosity...if all things being equal, how much could a person improve simply by losing weight. Is there a formula that could properly express this.
The numbers I'm working with are
6'3" my height
215 my current weight
23.4 my 50free scy time at nats last april

now my weight at nats was 215 after losing 20lbs over the season. I'm really paying attention to my diet and nutrition and trying to trim down another 10lbs.

Any thoughts???

fmracing
September 14th, 2011, 10:45 AM
I have lots of thoughts on this expressed elsewhere. Mostly opinion and hypotheses. I created a similar thread about this last year. Perhaps it could fill you in on what we already discussed...

How much does body weight effect swimming speed? - U.S. Masters Swimming Discussion Forums

Feel free to add commentary or thoughts to that thread as well.

knelson
September 14th, 2011, 11:51 AM
Just out of curiosity...if all things being equal, how much could a person improve simply by losing weight. Is there a formula that could properly express this....
Any thoughts???

My thoughts are: no way. There are too many factors at play here. If your weight decreases obviously you will require less energy to move you through the water from a pure F=ma standpoint. The other factor, though, is how your weight (or body composition) affects your form drag in the water. A higher body fat percentage will make you ride higher in the water, so having that additional weight is not inherently a negative like it would be in land activities like running. So you're kind of working on both sides of F=ma. Lowering your mass will require less force, but it's unclear how much force will be required to overcome drag at your new weight.

Allen Stark
September 14th, 2011, 12:06 PM
My thoughts are: no way. There are too many factors at play here. If your weight decreases obviously you will require less energy to move you through the water from a pure F=ma standpoint. The other factor, though, is how your weight (or body composition) affects your form drag in the water. A higher body fat percentage will make you ride higher in the water, so having that additional weight is not inherently a negative like it would be in land activities like running. So you're kind of working on both sides of F=ma. Lowering your mass will require less force, but it's unclear how much force will be required to overcome drag at your new weight.
Not to mention the momentum(p=mv) issue off the starts and turns.While it takes more force to accelerate you off the starts and turns,you maintain your velocity longer with greater mass.

arthur
September 14th, 2011, 12:22 PM
I think knelson is right. A formula is impossible as there are too many individual factors. For example if your stomach is smaller or equal to your chest size then losing stomach fat might not decrease the cross sectional area of your body moving through the water so your drag could be the same. If weight loss is not done properly it is also easy to lose muscle mass so you could become slower.

couldbebetterfly
September 14th, 2011, 02:58 PM
OK I'll admit it - I do have a degree in physics but found the whole fluid dynamics thing far too hard. Therefore instead of becoming a weather-girl I became an accountant!

As for the weight-loss, I found that I could easily maintain 130lbs and swim well, but try and get down to 125lbs and the effort, and feeling of weakness just made it not worth it, so it depends on where that 215 lies in relation to your ideal/minimun weight for your body type. You'll likely feel better in training and distance upon losing some weight, but probably not see much difference on a 50.

orca1946
September 14th, 2011, 03:10 PM
Physics - no. Maybe you lost the wt. & worked on strength more, so losing more will not always make you faster.

mattson
September 14th, 2011, 04:14 PM
OK I'll admit it - I do have a degree in physics but found the whole fluid dynamics thing far too hard.
Still working high energy experimental physics, but as others said, too many factors involved for swimming fast.

I sometimes notice swimmers skin rippling (around the shoulder blades) when they get a strong push off the wall. Losing weight may cause more loose skin, which may cause more resistance. Or what about weight gain, but it is all muscle mass?

pwb
September 14th, 2011, 06:46 PM
Just out of curiosity...if all things being equal, how much could a person improve simply by losing weight. I've been beaten by many people both heavier and skinnier than me, but, almost assuredly, those who beat me have some combination of better technique + better training + better talent.

I do think this idea is warranted, for health, life, happiness and swimming faster, even moreso as we age ...

I'm really paying attention to my diet and nutrition

... but am not convinced this...

and trying to trim down another 10lbs.
...will directly translate into better times for you in and of itself.

Focus on nutrition, focus on technique, focus on training and let the weight loss and speed be a by-product, not the goal.

rtodd
September 14th, 2011, 08:09 PM
As for the weight-loss, I found that I could easily maintain 130lbs and swim well, but try and get down to 125lbs and the effort, and feeling of weakness just made it not worth it

This is a good point. there is an optimum. Cut too much weight and you will lose energy. Lose a spare tire? yes. Try to reduce weight when you have no body fat? no.

Jazz Hands
September 14th, 2011, 08:10 PM
My thoughts are: no way. There are too many factors at play here. If your weight decreases obviously you will require less energy to move you through the water from a pure F=ma standpoint. The other factor, though, is how your weight (or body composition) affects your form drag in the water. A higher body fat percentage will make you ride higher in the water, so having that additional weight is not inherently a negative like it would be in land activities like running. So you're kind of working on both sides of F=ma. Lowering your mass will require less force, but it's unclear how much force will be required to overcome drag at your new weight.

I think F=ma is a non-factor in the water. Any of the swim strokes is a cycle of negative and positive acceleration. The negative acceleration comes from drag, which does not strictly depend on mass, although kind of indirectly via body shape like you said. Greater mass is a good thing in the slowing-down phases of the stroke, provided the drag force is constant, because the negative value of acceleration is inversely related to mass. Imagine throwing a ping pong ball versus a golf ball. Which one slows down faster? The flip side of this, of course, is that it's harder to accelerate in the positive acceleration phases of the stroke. But it should be a wash, right?

__steve__
September 15th, 2011, 12:22 AM
Aquatic mammals are generally not lean.

KatieK
September 15th, 2011, 10:24 AM
Even though I completely agree that this is impossible to quantify, I can't resist commenting...


I think F=ma is a non-factor in the water. Any of the swim strokes is a cycle of negative and positive acceleration. The negative acceleration comes from drag, which does not strictly depend on mass, although kind of indirectly via body shape like you said. Greater mass is a good thing in the slowing-down phases of the stroke, provided the drag force is constant, because the negative value of acceleration is inversely related to mass. Imagine throwing a ping pong ball versus a golf ball. Which one slows down faster? The flip side of this, of course, is that it's harder to accelerate in the positive acceleration phases of the stroke. But it should be a wash, right?

I think you're right, except for the push-off. Even though it takes more effort to push off if you have more mass, pushing off is pretty easy. So the additional "work" would not be any more fatiguing than if you had less mass, but you would generate more momentum.

(Not that this comment has anything to do with whether or not or how much weight loss would actually affect swimming speed in real life.)

knelson
September 15th, 2011, 11:05 AM
Aquatic mammals are generally not lean.

I'm not really sure this is 100% relevant. Aquatic mammals need a layer of fat so they can survive in cold water. I guess it does prove that animals can still swim fast even with lots of fat, but seals and whales aren't exactly built like humans, either.

pmccoy
September 15th, 2011, 12:52 PM
Here's my pseudo-science contribution to the thread:

* Drag forces are not directly related to mass but you still have to accelerate your mass to overcome the drag forces in order to maintain a constant velocity. F=ma does apply here. Being heavier hurts.

* While drag forces are not directly related to mass, they are related to cross-section and surface area. If you increase your girth, you increase your drag.

* Bouyancy makes a difference. Riding higher reduces the surface area and cross-section exposed to the water. Where you pack on that extra weight has a lot to do with whether or not this really helps. If only we could add fat in full body suit shapes.

* Pushing off a wall or starting block requires more force for a heavier person. You are accelerating your mass so there is really no getting past f=ma. Work is force applied over a distance. No need to go into that.

* I suspect there may be other forces at work other than drag. Wave generation is an interesting one and it turns out that being a little bigger might be an advantage. When you swim, you generate a wave. You actually make two waves, a bow wave and a stern wave. For non-planing boats, there's a point at which going faster becomes increasingly difficult due the interaction between these waves. Turns out the point at which things get harder is a function of the length of the waterline where a larger person would be better off. Don't know if this applies to humans swimming but I suspect it would.

My conclusion: It is hard to tell if packing on a few extra pounds really makes that much difference in swimming. Modeling a rigid body moving through the surface of the water is complicated enough. Accurately modeling a human thrashing about on the surface of the water is not going to happen with our current technology. So, there is not way to do a real objective analysis. We are left with anecdotal evidence like, "I shaved 2 seconds off my 50 free after I lost 10 lbs." Or maybe, "some fat guy blew me away in the 50 free last week. I guess the extra weight doesn't hurt him at all." It definitely isn't the liability it would be in running or cycling.

Allen Stark
September 15th, 2011, 01:51 PM
* I suspect there may be other forces at work other than drag. Wave generation is an interesting one and it turns out that being a little bigger might be an advantage. When you swim, you generate a wave. You actually make two waves, a bow wave and a stern wave. For non-planing boats, there's a point at which going faster becomes increasingly difficult due the interaction between these waves. Turns out the point at which things get harder is a function of the length of the waterline where a larger person would be better off. Don't know if this applies to humans swimming but I suspect it would.


"Hull length" definitely applies to humans.That is why there are so few short sprinters.This relates to height and not weight so has little applicability to the current discussion.

pmccoy
September 15th, 2011, 01:57 PM
"Hull length" definitely applies to humans.That is why there are so few short sprinters.This relates to height and not weight so has little applicability to the current discussion.
I think it is more a function of waterline... at least that is what we used to use to handicap sailboats. Height will increase your waterline but so will girth.

knelson
September 15th, 2011, 05:46 PM
you still have to accelerate your mass to overcome the drag forces in order to maintain a constant velocity. F=ma does apply here.

Exactly. Thus I'm confused why now two people are saying that F=ma does not apply. You must apply force to the water to accelerate your mass. Isn't that F = ma?

KatieK
September 15th, 2011, 07:03 PM
Exactly. Thus I'm confused why now two people are saying that F=ma does not apply. You must apply force to the water to accelerate your mass. Isn't that F = ma?
It applies--it's just that it cancels itself out. If you have more mass, you have to apply additional force to accelerate. But, because of inertia, the additional mass causes you to hold on to that momentum longer.

So, THEORETICALLY, the catch and the push-off require additional force, but they should take you further.

bcoomes
September 15th, 2011, 09:24 PM
Exactly. Thus I'm confused why now two people are saying that F=ma does not apply. You must apply force to the water to accelerate your mass. Isn't that F = ma?
In my case there is very little acceleration after the push off, velocity remains more or less constant. So a=0 (in fact, in my case probably a<0) after the push off. Force is applied to overcome drag.

knelson
September 16th, 2011, 01:30 AM
So a=0 (in fact, in my case probably a<0) after the push off. Force is applied to overcome drag.

You might be surprised to see how much you accelerate and decelerate through a stroke cycle.

__steve__
September 16th, 2011, 09:44 AM
In typical freestyle the swimmer almost completely stops and accelerates to the top swimming velocity (excluding push) every cycle. I saw this from datalogged swims on software which displayed both video and graphic representation, was very cool (Team Termin). Another interesting point is when your at your slowest velocity other parts of your body are accelerating like your recovery hand and shoulder.

pmccoy
September 16th, 2011, 10:22 AM
I see the argument against considering mass when accelerating against drag forces. The problem with that is it assumes drag forces (and other forces acting against the forward motion of the swimmer) are equal for both a skinny person and a fat person. I don't think that this is the case. It comes down to whether or not additional bouyancy overcomes and increased cross-section and surface area. I personally don't think it will but the math to back that up isn't something I'm ready to get into.

bcoomes
September 16th, 2011, 02:23 PM
You might be surprised to see how much you accelerate and decelerate through a stroke cycle.
There could be more intrastroke acceleration with respect to my center of mass than I am perceiving, but such acceleration should serve to increase my kinetic energy (1/2)m*v^2 (hopefully that velocity increase is mainly in the direction I am trying to go) and it seems to me that some of this kinetic energy bleeds off due to drag during periods of the stroke where I am applying little or no force and my center of mass is decelerating. It is difficult for me to visualize separating all the effects, but my intuition tells me that increasing m and keeping all other effect equal, should result in smaller velocity fluctuations throughout the stroke, but interstroke acceleration of the center of mass should be close to zero or even negative.


In typical freestyle the swimmer almost completely stops and accelerates to the top swimming velocity (excluding push) every cycle. ...


I could be missing some effect, but this does not seem right to me. I know when I miss a turn and the velocity of my center of mass drops to near zero, it takes quite a bit of work to get up to speed again. I feel nothing like that effect during regular freestyle. I can visualize parts of the body, especially the hands, having wildly varying velocities throughout the stroke. An accelerometer attached to any given part of my body would detect the superposition of the velocity of my center of mass and the velocity of that body part with respect to my center of mass. But it is not clear to me which is the greater velocity even in the case of an accelerometer attached near my midsection.

knelson
September 16th, 2011, 02:41 PM
I could be missing some effect, but this does not seem right to me.

I agree. Yes, there are big variations in acceleration throughout the stroke cycle, but if your velocity drops close to zero something is wrong.

arthur
September 16th, 2011, 03:40 PM
This is the post from TeamTermin U.S. Masters Swimming Discussion Forums - View Single Post - My freestyle technique, what needs work?

The images show a max velocity of about 2.1 m/s and a min velocity of around 1.5m/s during each stroke.