Body Suits and Performance by Dr. Rick Hinrichs (2003)


Published


Our second presenter is Dr. Rick Hinrichs – he is from Arizona State and will be presenting to you this afternoon on a variety of body suits.

Good afternoon everybody. I am going to change gears a little bit and talk about the biomechanical aspects of swimming, equipment, clothing effects. We were given funds from USA Swimming to do a study that extended work that we had done in the past on buoyancy in men versus women. We wanted to study just how men and women float differently in the water and see if that might affect how they swim through the water and after publishing a couple over the last five years on that topic it seemed logical then to look at whether or not swimming suits of any kind might affect how people float when they are swimming. So we were actually approached by USA Swimming to put a proposal forward to see if we could help shed some light on whether these new full body suits that came into vogue in the 2000 Olympic Games – whether part of the explanation that all of these records were falling – if anything has to do with the fact that they might be helping you float better – might be helping you ride higher in the water.

A lot of claims by the manufacturers that there is something to these new suits that help the swimmer float better in the water and that might be influencing whether performance is improved, but there have been no scientific studies of that. A lot of claims, but no scientific studies.

Before I go further I would like to acknowledge my co-authors, co-investigators: Scott McLane was my doctoral student originally who did this buoyancy study with men and women, it was his dissertation. He is now at Southwest University and my current PhD student, Brian Morrison who is a coach and sitting in the audience today is also co-investigator on this project and has done an enormous amount of work getting this to come to pass and the data you see today are largely the result of Brian’s efforts as well as the team, but Brian especially.

Let me give you some background. Part of the problem with the lack of science in this area is that if people are setting records in these new body suits – if there is something about the body suit that provides buoyancy or that somehow reduces drag – the question is should that be allowed? Was there scientific testing done on these body suits to see if they are buoyant before they were ever put and approved into the swimming pool – before the 2000 Olympic Games?

The rule says “no swimmer shall be permitted to wear – to use or wear any device – notice it says OR wear any device that may aid in his speed, buoyancy or endurance during competition” and it does provide some examples of which body suit is not on there because the rule was written well before that, offering something such as webbed gloves, flippers, fins, etc, so the etc. could potentially include body suits and the question that had never been answered and we hope to be able to provide some answers for you today is do body suits aid in speed, buoyancy or endurance?

I think the aiding and the speed part has been shown through a couple of different studies that have actually measured the drag during towing of a swimmer through a pool. There have been a couple studies that have measured drag and actually showed reductions in passive drag of body suits. The one that has been studied the most is the Speedo Fastskin suit and if there is the drag aspects – the pure – lets call it skin friction – the drag aspect is if you can put on something and you are now slipperier than you would have been had you not put it on then that is another aspect of it that I am not going to talk about today. Other people have done it – it is a different study – I would like to do it with all of the suits that I am going to talk about today, I would love to be able to tell you about whether the skin friction part is less. I do not have that data, but overall the question that we need to ask is should body suits be subjected to scrutiny based on this rule of FINA?

So the purpose of the study was to investigate simply the buoyant aspects or the buoyancy affects on the body of body suits and we studied body suits from five different manufacturers. That is what makes this study a little different than in the past is that everybody and their brother has been focusing on Speedo – well there are a lot of other body suits out there besides Speedo. In fact, there have been two studies published just in the last year and a half or so that have actually shown in a limited test of buoyancy that the Speedo Fastskin did not provide a net buoyant force over what you would get just with a conventional swim suit so that was part of the motivation. In fact – when we first proposed this we proposed to study Speedo suits and USA Swimming said “no, we want you to study suits from all the manufacturers” so we expanded our study to include Adidas, Arena, Nike, Speedo and TYR and understand there is yet another manufacturer out there who unfortunately we were not able to get that suit included in this study – maybe in a future study.

This is what we did. We had 30 subjects in our sample; 14 men and 16 women. They were at Arizona State University either on the varsity swim team, on the masters – the Sun Devil Masters Team or other swimmers that hang out near Mona Plummer Aquatic Center or close by. This seems to be a nice you know, focus of attention. A lot of swimmers come by there. the only restriction is that we sought and got human ______ approval for adults only so even though we had kids that wanted to participate we did not get anyone who was under 18 years old. We did get some high school seniors who were 18 complete the study and they all signed – we were given informed consent and signed informed consent forms.

These are examples of the suits for women – you can see, I mean, you may already be this audience here – the nice thing about speaking to a group of swimmers and swimming coaches is that you already know the issues. You probably already know the suits. You know what they look like. The only one that really differed much between the appearance of the mens and womens suit – here is the mens – is the Arena. You notice for the women there is a sort of a gray and the second from your left – a gray torso part just for the nice little art design here and it is just black for the men. Now what I didn’t show you is on the back side the Arena suit is also a little different for men and women as well, but the material is the same, even though it may look a little bit different. We got body suits that were primarily from the torso that was not covering the arms except for one manufacturer, the Adidas, suit did not have an equivalent torso, but no arm suit so you can see that the Adidas suit went all the way down to the elbows. We got on the right – the conventional suit we got from Speedo and all of these suits were purchased – many from retail outlets right there in Phoenix – none were donated.

One of the things that we needed to do was to measure where the center of mass is on these swimmers because we wanted to not only study the buoyant force on the swimmer but also where the point of application of the buoyant force – the center of buoyancy on the swimmer.So the first thing we had them do was all the swimmers lay down in a prone position on a board that is called a reaction board and it is – you will see it later on in the slides – have an actual picture of it but lay down on your stomach. We would have the ankle joint here, the lateral malleolus right over this particular knife edge that has the beginning of the board. At this end of the board there is a scale that is actually measuring force. The way that the reaction board works is it takes how much of a person’s body weight is reflected at this end of the board compared to that end of the board. So we would weigh the person as well and the weight of the board is sort of subtracted out of all of these measurements to start with, but when lying on this board, if 50% of your weight of a 150 pound person – lets say if this is 75 pounds and this is 75 pounds, obviously we only need to measure one end because we know what the total is – then the center of gravity or the center of mass is half way between the two so it is exactly half and half when you have 75 pounds and 75 pounds. If you had something that was 2/3 of the weight on one end and only 1/3 of the weight on the other end then the center of mass is actually 2/3 of the way between the two ends – it is that simple. So, it is a simple reaction board measurement.

We found out that the centers of mass of these swimmers are just about where you would think they would be in terms of the information in the literature, but we also found that there was very little variation at all due to the body suits. So that the body suits themselves didn’t change where the center of mass of the person was. The variation between suits – due to the body suit – was within the variation of repeated measurements with the same suit so rather than add additional variation we, after doing 8 subjects out of our 30 with all the suits – we decided to use the value for the conventional suits – the center of mass for the conventional suits and assume that , that is the same across all suits because it didn’t change by an amount that was larger than the normal variation and repeated measurements.

Now here is Brian with a swimmer. This Is Mona Plummer, Aquatic Center here at ASU, Sun Devil Stadium is behind the pool there and he is helping to steady one of our swimmers in what is called – what we like to call our under water reaction board. Now it is not a board. It is straps and the straps are actually holding onto the swimmer here, this is a different view – right underneath this reaction board. The swimmer that is held up by straps and the straps are cinched tight around the shoulders but in a very easily reproducible notch between the deltoids and the latissimus dorsi. We cinched it there, around here and also down – the distance between the two, between the two straps here is 1 meter so we put a mark here at this point and put a mark on the legs 1 meter away. Then we would have the swimmer get in the water, hold a streamline position like this, blow out all of her or his air and hold steady while a little force transducer measured how much force was required to hold the person up.

Now granted, some people float better than others, especially between trials where they had to come up for air and so each of these two straps has weights hanging down of which we then knew how heavy it was without the swimmer. We could subtract that out and get a net weight from the swimmer and what we are getting is under water weighing in the swimming pool in effect so we know how much a swimmer weighs. We know where the swimmer’s center of mass is. We know how much force is at this end and we know how much force is at this end – we can get the upward buoyant force that this swimmer’s body is sustaining – that is our first variable is buoyant force. Then if we know where the center of gravity is between the two we actually can get our fourth variable and this diagram shows here how we actually get it.

This is from an under water camera actually showing a swimmer in a streamline position – you can see the straps here and you can see that there are weights down below each strap. There is 1 meter exactly between the two and this is a free body diagram – FBD. A net force S1, a net force S2 – remember after the weights have been subtracted out we know how heavy the swimmer is and where the center of mass is of the swimmer relative to the bottom of the feet here and then the only two unknowns are the buoyant force and the location of the buoyant force DCB. Those are the two variables that we got – buoyant force and center of buoyancy location.

And here are our results: This shows data from men and women combined. Because we found no overall difference in the way that the suits responded to the men’s and women’s bodies.

The fact that they were the same manufacturers with the same material, even though the bodies are different – the men are less buoyant than the women in general. We were able to show that, but this is what the results showed across men and women together for body suits.

First – look at this dotted line right here this represents what happens over four minutes in the water with a conventional suit. The buoyant force for the conventional suits stays the same over 4 minutes of water at about 98% of your weight. 98% of the person’s weight is now buoyant force. Remember, this is fully exhaled. People sink when you are exhaled. We did not do this with a full breath of air. We wanted to be consistent and blowing out all your air is much more consistent than how much do you get a full breath you know, across two hours of testing are you going to take the full breath the same every time. So we judged that it was best to be controlled and blow out all your air.

The body suits from five different manufacturers generally followed this trend, but not completely. There was an excess buoyant force at minute 1 for most of the suits and it generally decreased over time so that we had these tests done after a person got in the water we tested it at one minute, just for maybe a few seconds of collecting data and then stopped, rested, came up, grabbed a hold of the wooden board and then when a minute went by, went back again and blew out all the air again and took another reading. You can see for example the Nike suit which had the highest buoyant force at minute 1 dropped off and in the second minute now was down to about a 98% of body weight and the third minute dropped down and the fourth minute dropped down, but even after 4 minutes still a slight buoyant affect compared to the conventional suit. Speedo on the other hand had a small buoyant force to start with. After a minute the buoyant force was gone and then proceeded to be negatively buoyant after 4 minutes so right here, this data on Speedo helped explain why other studies have not found a buoyant force because other studies have not done a time element over which; they just put the swimmers in the water and there is no particular statement as to how long it was after the swimmer hit the water to where the buoyant force measurements were taken.

This one, TYR, was basically negative buoyant. It started out neutrally buoyant and ended up slightly negatively buoyant so that the TYR body suit did not provide any buoyancy at all, in fact slightly negatively buoyant and we are left with these two: Adidas and Arena. The Adidas and Arena here started out a little you know, moderately buoyant, maintained buoyancy and then Adidas dropped off a little bit, Arena maintained. Arena did not drop off at all.

That was very interesting so there is something different in the way the material absorbs water or doesn’t absorb water, but the overall affect is that this – the data – time 1 were statistically significantly higher than the data all the other times. In other words, the buoyant effect generally – if you go out and you buy a body suit, the buoyancy affect is real, but short lived for most suits and that explains why maybe people who wear these suits, mostly in the sprint events or in the middle distance events. You don’t see that many people wearing these in the mile – maybe there is a reason.

Now these combined now across all the times so in order to run the most powerful statistics we looked to see if there were interactions so that we could get at the main affects and if like the men and women responded similarly for these buoyant forces. So we didn’t test the men and women separately, we put them together so that we would get the greatest statistical power and this should be a reflection on the previous slide.

This is like the overall affect over 4 minutes – like the average across 4 minutes and you see Adidas, Arena and Nike were the three that provided the highest buoyant forces and this is now expressed relative to the conventional suit so zero. Zero now means the same as the conventional suit. The men and the women have slightly different you know, buoyancies.

The women were more buoyant than men, but when you compared to the conventional suit everybody starts at zero. Above zero is buoyant, below zero is negatively buoyant. Three suits are statistically significantly buoyant; Adidas, Arena and Nike.

Speedo a little bit, but not significantly so and TYR – a little bit negative as you would expect from the previous slide. So these two here were not significantly different than the conventional suits so you cannot say that that is buoyant and that is negative with buoyant there – just essentially the same as the conventional suit. Given the statistical variation that we normal see, but these three they are the ones that provide positive significant buoyant forces and I will come back to that because there are some implications about this rule now.

Just for completeness I thought I would show you how the mens and womens data looked – even though we did not run statistics on these. This is the data for men – you can see the men tended to do better in Nike than Arena, but these three generally are the highest ones and you can see Speedo and TYR were lower in the men, as they were overall, but notice that there is a lot of variation here also for the men and that variation is much smaller in the women.

The women’s responses was instead of Nike being the biggest one, Arena is the biggest one for the women but the three suits still have the same basic trends – Speedo and TYR are the ones with the least amount of buoyant force and so when you compare. This is the average of men and women and that gives you the best overall confidence in the results because there was no significant interaction between men and women and the suits – that is the men – that is the women, so you can see how the Nike is low for women and Arena is high for women. Nike is high for men – well relatively high for men and low for women and overall you get this average that makes these three basically all the same and then these two providing no buoyant affect. That is the buoyant force data but the second part of this is how about where the buoyant is applied.

If you have the same buoyant force but you can apply that buoyant force closer to the center of mass so those two forces line up. This is what happened.

This is what happens when they don’t line up. Let me show you that first. This is a just a schematic from one of our prior publications when Scott McLane and I did just about men versus women and it is explaining why your feet sink. Stay motionless on your back. There is no way you can do it and stay horizontal. You either cheated by sculling with your hands so you could keep your feet up or you let your feet sink like this and why did your feet sink? They sank because the buoyant force and the gravitational, force are offset from each other. These two forces have a —— arm between them and they produce a couple or a torque that tends to make, in this particular case it tends to make it rotate clockwise. Your body will rotate under this torque until this ——- arm is reduced to zero and when those two forces line up over each other all of a sudden you no longer have a torque that is making your feet sink.

Now in real swimming, during actual swimming it is not like floating on your back. Part of your body is above the water. We don’t have this exact same thing going on but it does apply every time you are pushing off gliding or where part of your body is not above the water. This is modified by having part of your body above the water, but the affect is still real and so we now know how big that force is. Now we need to figure out how big that distance D is. We have the data from our under water reaction board.

Okay, now for the center of buoyancy data it turns out there was a significant interaction between men and women across suits so we cant combine them together. Men and women are different in their center of buoyancy location and how the suits affect the center of buoyancy so these are the data for men, but we did collapse across time because we didn’t see any significant interactions with time now so this is across all four minutes. Zero means where the center of buoyancy lies where the conventional suit is and things that are negative now are desirable. Negative means that the center of buoyancy is now moved from the – well it is never up in the chest it is actually only about a cm. or so or two cm/s from the center of mass but negative means it is moving down towards your feet, closer to the center of mass.

We find, for example that the Adidas suit center of buoyancy was basically right where it was with the conventional suit. The Arena dropped it down – now this is in percentage of your height so if you have – we are dealing with 1/10 or 2/10 of a percent of your standing height so it is a small – we are dealing with a mm or two or three change. They are small but our system can precisely measure this. Granted, there is a lot of variability and this variability made it challenging to get significantly different data – significant results so even though we have what looks like big changes from the Arena and the Nike and the Speedo suits – only TYR suit had data that proved to be statistically significant.

Isn’t this interesting – the suit that provided no buoyant force provided the greatest center of buoyancy affect so even though it didn’t lift you up altogether – by the way – I need to say this is men – the data for women are different – totally different. So for men they tend to have their feet sink more anyway even though the TYR suit didn’t give them any help overall. The TYR suit helped shift that buoyant force so that they were more horizontal and not floating is I guess the best way to say it. They were not given any additional floating ability, but it helped keep their feet from sinking as much in terms of the buoyant torque there.

Alright, now for women and notice these are on the same scale. The men were down to 3/10 of a percent of , your standing height and these are air bars here or standard airs. The women have substantially smaller center of buoyancy – the center of mass distances anyway. Women typically float horizontally in the water. Their center of buoyancy and center of mass are almost lined up already. Those people that can just float completely motionless horizontally there is like no distance between those two points horizontally, to start with so women already have a small distance but the body suits did help a little bit to make that small distance even smaller. Notice it is not the TYR suit that did it. There was only one that was statistically significant and that was Adidas.

It provided the largest change in the center of buoyancy location – not far behind are Arena and Nike – Speedo made almost no change and TYR just a little farther behind or a little behind the Nike and the arena but remember with the variation that is about the same size as the mean – it is hard to get significant results when you get normal variation in there between subjects.

So, once again this is what the men’s data looked like – these suits appear to make the biggest difference on the men – in terms of this variable. This is what the women’s data looked like. One of them was statistically significantly different than the conventional suit.

Lets summarize it. We found no significant gender suit interactions for the buoyant force meaning that these suits appear to affect men and women similarly when it comes to helping them stay higher in the water as a whole. The three suits; Adidas, Arena and Nike provided significant positive buoyant forces compared to the conventional suit. This information has not yet ever been found because only the Speedo suits have ever been studied in this regard that I know of, at least in the published literature and the Speedo suit we found was not positively buoyant. We did find time effects – the buoyant forces were significantly larger at the first minute than they were in minutes two, three and four. That may explain why swimmers finding the most success in sprint events that occur within a minute or less.

On the other hand the Adidas body suit seemed to hold the buoyant force a little longer than the others; it kept it for two minutes before it started to fall. And then the Arena body suit is the one that was a little different still. It kept its buoyant force for 4 minutes. We stopped our test at four minutes. We have no idea how long the buoyant force lasts but there was no sign that it was dropping off of course. We do not know. We cannot say what happens after 4 minutes. already our subjects were there two hours – imagine – we would like to test it for 1500 meters but then the subjects would basically be in the water 8 hours to be able to do all these various tests, but somebody needs to do this for sure in the longer races because we need to know whether the buoyancy effect is really there. It could be very important for longer races if a buoyancy effect stays. Now what is the summary of results for our center of buoyancy?

Well, here the men and women behave very differently in how the suits responded to their center of buoyancy locations so we analyzed them separately. The men had larger variation so it made it a challenge to find significant results, especially for men, but the data – there was a greater distance of which to move and so there would be a greater effect on the men than the women from these suits. For the men, the TYR suit provided a significant shift in the center of buoyancy position compared to the conventional suit that would tend to help have your feet sink less. For the women it was the Adidas suit that provided a significant shift, but remember they are all fairly similar. I am not entirely sure of the fact that one is significant and one is not necessarily means that that is an important difference.

There were trends, but no significant changes over time and let me tell you, I didn’t show you the graphs but the center of buoyancy effect also tended to decay over time, but it was very, very gradual and with the variation there were no significant differences so there were trends over time meaning that the same thing that would provide a buoyant force if that got less over time the same thing that might make the center of mass or center of buoyancy get closer together, they tended to get farther and farther apart over time, but very, very small changes and so we cannot say anything about them, whether they are real or not at this point.

Now, in conclusion, I want to go back to this FINA rule and I want to bring up an issue about wet suits before I leave you here. Do you know that wet suits are banned in normal USA swimming competitions – wet suits are allowed in certain triathlons and open water swims, but you cant swim a 50 meter freestyle with a wetsuit on. I was having a discussion with Brian at lunch about whether you would want to swim a 50 meter freestyle with a wet suit on because most people that have studied wet suits have seen that it provides buoyant force of a substantial amount that helps distance swimmers and a distance swimmer can go faster with a wet suit on and that is a known fact – it has been shown in research.

The thing is, FINA, because of this rule bans wet suits in normal competitions so if that is the case some body suits, specifically Adidas, Arena and Nike appear to act like wet suits. They provide a significant buoyant effect. How big is that effect? Maybe 1/10 as big. We have actually done some calculations of body density among our swimmers. I am showing you buoyant forces. In order to get body densities you actually have to know what the residual volume is and we didn’t get residual volumes – we got residual volumes on 8 of our swimmers, not 30 so we haven’t done body density calculations on everybody but for those 8 swimmers it shows that maybe these buoyant forces or the buoyant effects are about 1/10 of what a wet suit does.

Now the question is why are buoyant body suits allowed when buoyant wet suits are not? I am going to have you ponder this a little bit because somebody is going to have to discuss this at some point and my final statement is that FINA might want to reconsider or reinterpret this rule in light of this research. Thank you very much.

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