Asymmetrical Force Productions During Swimming Starts by Richard Hinrichs, Ph.D. (2006)


Published


Thank you for inviting me to speak to you. I want you to know that I was a swimmer, then a swimming teacher, and then a swimming coach well before I ever got into the science side of things. I will try my best to get to the coaching and swimming applications here, because I know that you are most interested in what the research ultimately has to tell us about the various swimming starts rather than discussions of the biomechanics of the starts.

I brought a couple of slides of Arizona State University. For the most part Arizona is, as you know, a very dry state. They say it is a dry heat and it is a great place to do swimming research. The sun shines almost every day of the year and we have to worry about sun exposure, but it also attracts a good group of people to our lab for our swimming research, four people in particular.

Today, I will talk about some of the work that Rob Welcher has taken the lead on and that will be called Study #1. I will also refer to Study #2, ongoing work by Sara Consty, who has just graduated. Scott McLean and Peter Vent, former PC students continued to participate in the study while they were at other universities. Peter is now at the U.S. Olympic Committee in Colorado Springs.

Let me give you some background about swimming starts. Most of you already know about the most popular ones. I am including one in the list that is still used in relays for the 2nd, 3rd and 4th swimmers. I swam the breaststroke in college in the early 70’s about the time that people were changing from a full arm swing start to the grab start in which you restrict the arm swing by grabbing the blocks.

The grab start began in the late 60’s and started becoming popular in the 70’s, but I never felt comfortable using it. I wanted the benefit of a full arm swing to get me farther out over the water and into a nice long pull-out. Perhaps I could have been faster with a grab start, but the fact was that starts were always the best part of my race, and I was always a body length ahead of the next person coming out of my pullout on breaststroke.

I never experimented with the grab start until after I was out of college–actually, until after I was out of grad school. Some people were telling me that I was really doing an old start, that I was getting a late start because at the gun of my big arm swing. It might have been true. There are still some master’s swimmers and some age group swimmers who use a conventional start from the gun, but I do not know of any highly competitive swimmers who are.

In the mid-70’s and late 70’s, the track start became popular and, as you know, in the track start, instead of keeping both feet symmetrical and at the front of the block as in the grab start, the swimmer puts one foot forward and one foot back. I think the original idea was to try to mimic what a track and field athlete might do on the track, but to do it on a block into a swimming pool.

There have been more recent starts. In one, which I will call the rear way to track start, the swimmer leans back and, thus, begins from the front of the block instead of right at the front of the block. There are variations, which started becoming popular in the 1990’s, that range all the way from leaning forward, to leaning back, to somewhere in between.

This slide attempts to show the diagram of the body positions in the various starts. We studied the grab start where, for the most part, the swimmer is symmetrical and can put the hands on the inside or the outside of the feet. We didn’t restrict the swimmers in our studies to doing one or the other but, when the gun goes off and the swimmer pushes, the two feet push simultaneously.

The title of my talk has to do with asymmetrical force productions, but a grab start is an example of symmetrical force production in which two feet pushing after two hands are symmetrically pulling. However, we have actually done measurements with forces and found that, even in a grab start, there is a high degree of asymmetry between left and right hands and left and right feet.

We wanted to look at the two extremes of the track start. One is what we are calling a front way to track start where there is one foot back and one foot forward and the hands are on each side, similar to what they would be in a grab start, but they are not necessarily in the same position because now there is only one foot to deal with. As a result, in the track start, the swimmer has a greater range of positions for the hands.

The difference between the front way to track start and the rear way to track start is that, in the rear way, the swimmer leans back, putting more weight on the rear foot. In the front way, most of the weight is on the front foot and the center of gravity or the line of gravity is closer to the front edge of the block. In other words, the swimmer is almost falling forward but is being held by the hands. But, as soon as the line of gravity actually falls outside of the base of support, unless there is something else to hold onto like a handle on the starting block, the swimmer falls forward.

When the swimmer is leaning back, the line of gravity has a greater distance to move forward before it and the swimmer fall off the front of the block. The slide shows that both feet are still in contact with the block. These photographs were obviously taken before takeoff, but notice that both feet are pushing and then, slightly later, when this slide was taken, the rear leg goes off and only the front leg pushes. These are examples of asymmetrical force productions among feet.

Various people have had success with all of these kinds of starts and research has not shown which one of the three varieties, the grab and the two forms of the track start is better. I was delighted to see this picture, called “Parting Shots,” on the last page of Swimming World magazine last month. It is such a good picture because it clearly shows only one foot pushing.

So, how is it that you can push off with only one leg for much of the start and still generate power and speed? The question is sort of a catch-22 and it is naïve, as well. When I was scanning the picture in preparation for this presentation, my wife asked if the swimmer could possibly be as fast? Why would any swimmer want to push off with only one foot for much of the start? The answer is hypothetical, but it is based on research: it may have something to do with what is called bilateral deficit.

Bilateral deficit means that if you were to sit at a leg press machine to see how much weight you could press and with both legs you pressed 200 pounds, you would then expect to press 100 pounds with each leg alone. But that is not true.

When both legs push simultaneously, it is called a symmetrical bilateral effort. After you are fully rested so that there is no fatigue and you do the same leg press, but with just one leg, first–the right leg and then the left leg in a unilateral exertion, you would think that you could do half as much with one leg as with two. In fact you can do more. Instead of 100 pounds, you might be able to press 110 or 120 pounds with each leg, and when you add the two legs together you get a larger number than you would have gotten from two legs pressing together.

Because two legs pushing together can’t do as much work as the sum of two unilateral efforts, they call the difference the bilateral deficit. It is possible that one of the reasons that this asymmetrical force production in the track start could be useful is that the swimmer has two legs doing different things. Perhaps the brain thinks that the swimmer is having two unilateral exertions, and it is getting more out of those two legs than it could if they were doing their work together. This is the hypothetical basis for much of this discussion related to asymmetrical force production.

So, let me summarize what I think the literature has found so far in terms of the disadvantages and advantages of the start. The conventional start has the advantage of greater speed off the block. The action of swinging the arms generates the speed—even from a gun. Today, it is used only by the 2nd, 3rd and 4th persons on a relay when there is not a reaction time to worry about. It should be used in a relay because of the speed it generates.

In my opinion, anybody who does not practice the conventional start is missing a good thing because the forward momentum generated by the arm swing allows the swimmer to push harder against the block with the feet. It gives the swimmer greater speed off the block, at least theoretically, and the literature does support this.

The problem with the conventional start is the swimmer’s reaction time to the flash start of the gun. There is a time cost. The swing-arm start takes a longer time to get off the blocks in the first place, which is why the first person in a relay might not want to use it. But, the 2nd, 3rd and 4th people should use it–if they time it just right–because there is no gun.

So, the grab start has an advantage since there is no arm swing and the swimmer actually gets off the block faster than someone doing a conventional start. But, the problem is that without that arm swing there is less speed at takeoff. When the conventional start was first compared to the grab start, studies showed that the grab start produced less speed but a faster time off the block. It appears that the advantage of a faster time off the block offsets the disadvantage of a slower speed off the block so that, in the long run, most people perform faster with the grab start.

Front and rear track starts. Now, lets extend this discussion to the front way and the rear way track starts. The front way to track start appears to have even a bigger advantage than the grab start in terms of getting your center of gravity right up to the front edge of the block. People who have studied this front way to track start have shown that there is even shorter time off the blocks. You can get off the blocks even faster with a track start than with a grab start. The fact that you have one foot forward and one foot back gives you added stability. You can find the right position, you are not all lined up, and you don’t have the ability to adjust to your line of gravity over a larger distance.

There is a problem, though, in that if you are moving the center of gravity all the way up to the front, research has shown that there is less speed off the blocks when you are just about to fall forward. This occurs because you don’t have as much time to push against the block and, consequently, you don’t go quite as fast off the block.

Now, this is where the rear weighted track start starts to solve some of those problems, but then perhaps adds some additional problems. Because you are leaning back in the rear weighted track start, it appears you get to generate forces for a longer period of time and to get more out of your hands thus getting greater speed off the blocks, sort of like the conventional start but without the cost of the long arm swing. The problem is that the disadvantages are the same—there is still a greater distance to move forward before you leave the blocks. But, these conclusions are all based on past research, common sense, and mechanical principles.

We wanted to see what we could do to add to this body of knowledge in the two studies I will discuss. One is completed and the other is underway. We wanted to compare the grab start with the front weighted track start and the rear weighted track start in terms of block time, timed to 5 meters and instantaneous velocity, both off the block and at 5 meters. We chose 5 meters because there is a period around 5 meters where people start to kick and thus to add something to their normal start. We wanted to see if we could remove the kick from the study so our swimmers actually glided past 5 meters before they started kicking. In the second study, based on the limitations of our first study, we wanted to add force measurements and to come up with a means of measuring the separate forces generated in these starts by each hand and each foot to explain why one start might be better than the other. We also wanted to understand the nature of asymmetrical force distribution to see how the left foot and the right foot were different and potentially how the left hand and right hand are different as well.

Rob Welcher helped us with Study #1. He is now a varsity coach for men and women at the University of Wisconsin Eau Claire. He actually collected the data when he was working on his master’s degree at the University of Michigan in the mid 90’s and then we analyzed it after it came to issue in the late 90’s and early 2000’s. He used women varsity members of the University of Michigan who averaged about 20 ½ years of age. All the subjects signed a consent form.

One problem in conducting research comparing different techniques of motion is the varying levels of experience of your subjects. Some people are more experienced with one kind of start over another. Some people are really good at grab starts and others are really good at track starts. So, Rob surveyed each swimmer to determine her experience with each start and her first, second or third preference for starting technique. Because these were experienced Division 1 women swimmers, we didn’t want to express a preference. We wanted instead to see how they did with the various starts given their experience and abilities. Thus, no training was provided, although some instruction was given right before data was collected to those people who had no experience with a particular start, such as the rear weighted track start. Rob explained it to them, gave them three or four practices, and then begin to collect data.

We used above-water and below-water video cameras and the starting signal was marked on the above water-video camera only. That turned out to be an oversight, but we were able to synchronize the above- and below-water cameras by looking at the instant that the finger tip went to the surface of the water on both cameras. We were interested in getting the time continuously through the air and under water to 5 meters. The above-water video was analyzed frame-by-frame and digitized by my selecting on a computer screen points on the body that can be repeated like the elbow joint, the wrist joint, and the shoulder joint. In total, there were 21 points on the body on every frame.

You can use that with some information on the master’s division of the body to come up with the center of mass or center of gravity for each instant of time while the swimmer is on the block, the take-off from the block and then under water because swimmers, for the most part, maintain a constant body position. We digitized only the hip point because if the body were not changing positions, the hip would be moving at the same speed that the center of mass is moving. We measured the time that the hip marker crossed the 5 meter mark and we measured the instantaneous velocity at the 5 meter mark.

The results indicated that the front weighted track start, FWT, had a significantly shorter block time. When I say “significantly,” I mean that we ran the data through a statistical program so to see if there were statistically significant differences between different numbers. As in previous research, the front-weighted track start was found to be faster than either the rear-weighted track start or the grab start. Those were both 87/100’s of a second. The front-weighted track start had a 7/100’s of a second advantage in getting the feet off the block in the sample of college women and their horizontal velocity as measured from the video.

The rear-weighted track start, RWT, produced a significantly higher velocity at takeoff, 3.99 meters per second, than either the front-weighted track start or the grab start, which is also consistent with the theoretical background that I gave you. When you lean back, you have a greater time in which to pull with the hands and to push with the feet. When you leave the block in the rear-weighted track start, we found that it was 9/100’s of a meter faster at the time the swimmer leaves the block than either the front-weighted track start or the grab start. But we also took another snapshot at 5 meters under water to see if any of this translated into significant differences. It turns out that the amount of time from the starting signal until the swimmer’s hip passed 5 meters did not differ in any of the starts. There were no significant differences. There were some numerical differences–the grab was 2.24 seconds, the front-weighted track start was slightly faster at 2.19, the rear-weighted track start 2.21, but there was enough variability between people and between starts that there were no significant differences. In other words, no start had an advantage in terms of reaching 5 meter over the other starts, but that is not the whole story.

The rear-weighted track start produced significantly higher velocities at 5 meters than either the grab start or the front-weighted track start. Let me just say that, statistically, the speed of 2.25 meters per second was greater than 2.18 meters per second, the speed at which the swimmer crossed that 5 meter mark. Even though the rear-weighted track start was behind a little bit at first, it caught up and was in the process of passing the other two at the 5 meter mark. Now, there was a trend towards the higher velocity of the rear- weighted track start compared to the front-weighted track start that is 2.25 compared to the 2.21, but it was just on the edge and we cannot call it a significant difference. If we had had more subjects, it probably would have been a significant difference.

So, in other words, there was something to be said for this rear-weighted track start. Even though it produced higher velocities at the takeoff, it took longer to get off the blocks. It still generated faster speed even though the others had a head start crossing 5 meters. Faster speed should mean that it is the superior start. You might say that maybe these people were just better at the rear- weighted track start that more of them were experienced with it. But, that was not true. Since the data were collected in 1995 when this first study was done, the rear-weighted track start really wasn’t popular yet. In fact, many people had no experience at all with it.

Of our subjects, 10 people had substantial experience on the grab start, whereas only 4 people had substantial experience with the rear-weighted track start. Almost as many people had tried the track start, but they had tried it when it first came out when it was intended something in which you just got your body ready to fall forward at the front of the blocks. Hardly anybody had experience, 13 of the 19, had no experience or very little experience with the rear-weighted track start. In other words, we were getting good results for a technique that these people had not even tried before.

If we compared the results to the preferences, you can see the front-weighted track start was what most people thought was the best one. Only 4 people thought that the rear-weighted track start was the best and yet 11 people were actually fastest with the rear-weighted track start–meaning fastest at 5 meters under water–and 7 more people were second fastest with that particular start. In other words, 18 of the 19 were either fastest or second fastest with the rear- weighted track start and yet only 4 people had any kind of experience with it. So, what this means is that if we took a group of people that actually had practiced this rear-weighted track start, and if it is like similar research done on other sports where experience is a big confounding factor, my guess is that these results would have been more impressive than they are now and in favor of the rear-weighted track start.

So in conclusion for our first study. The rear-weighted track start was the best start overall based on all of the measures. It achieved the fastest velocity at 5 meters at the same time as the other starts, which means that just slightly past 5 meters the swimmer who used the rear-weighted start is going to be ahead. The swimmer reached 5 meters at the same time as the swimmer using other starts, but was moving at a greater velocity. These results were achieved with little or no familiarity with this start among the subjects.

There are some limitations. The sample is all female and, at that time, more women were experimenting with the track start than men. I think you are finding that the distribution has caught up a little bit. When it came time to publishthis study, the reviewer said “Well, okay. Did you measure forces?” and gave us the idea of trying to explain what is going on during these starts. Why was it that the swimmers could get off the block just as fast off of one foot–at least for a good portion of the start–than they could with two.

So, in Study #2, we began to study the forces involved in these starts with the help of a grant from USA Swimming. We wanted to measure both men and women this time, and we also wanted to see if there was a difference in the results of non-competitive swimmers who were taught a start and the results of competitive swimmers. From our sample of 30 men and 30 women, 15 men and 15 women were non-competitive swimmers. They had no real experience in swimming starts and they had not competed in swimming in a long time. These non-competitive swimmers underwent three weeks of training to learn these various starts.

In addition we wanted to use similar data collection for the video portion. The strong point of the other study was underwater and above water videos simultaneously, but this time we wanted to make sure that we had a starting signal visible under water and above water so we wouldn’t have the uncertainty of knowing exactly when the fingertip went through the water. To do this, we had a single button that started sampling on the computer, made a sound for the swimmer, and simultaneously started lights above and under water.

To study the forces, we created a custom starting block with two AMTI (Advanced Mechanical Technology, Inc.) force platforms that we normally use in the lab for studying vertical jumping. We bolted them to the top of the starting block and placed side-by-side, they had dimensions similar to the actual starting blocks the swimmers use. They were a little bit wider, but about the same depth. The biggest equipment challenge was special hand bars for getting separate left and right hands measurements. The problem is that during an actual start, the hands grab exact what the feet are pushing against. They are just a little bit to one side or the other and so to be able to have an isolated hand bar where the hands are not touching the force platform was a challenge and a problem on which we are still working. We believe the velocity of takeoff can be probably more accurately measured by using the force record than by analyzing video tape because the force records are very precise. Over time, we should be able to integrate the forces to get the velocity at takeoff.

So, this slide is an actual frame from some pilot testing that we did. This is a doctoral student of mine who is one of the non-competitive swimmers, and underneath the towels on the starting block are two force platforms. There are handrails in front that are, at least at this point, a little bit in front of the starting blocks and also below. Although they are not typical of a real start because the hands are a little bit lower than they normally would be and a little bit in front, we placed them there so that when the swimmer pushed back on them the palms of the hands did not also touch the force platform.

This next slide is a close-up of that. Here are the two AMTI force platforms mounted at an angle of 8 degrees, which is within the acceptable range of angles. These are the same angle as ASU’s starting blocks at the Mona Plummer Aquatic Center. To use them, the swimmer puts a left foot over here and a right foot over there and a hand on each of the two hand bars here. We could adjust them left or right, but we are in the process of redesigning them to make them a little bit higher so that the swimmer doesn’t have to reach down quite so far. One limitation of our first round of this was that, while we got some interesting results, we think that the hand forces may be incorrect, partly because of where the bars are placed and also we had a design problem with these load cells.

But, let me give you some of the preliminary information, based on what Sara Consty did for her master’s thesis. She studied only women for her thesis and in the second round will do the same thing with men. I have the data on women but apologize for not yet having the data for men. The results are so far only for female subjects, and, with one exception, we were able to replicate all of the results that Rob Welcher gathered.
It is interesting that when we compared competitive swimmers who were treated like the Welcher study and already had some familiarity with the starts to the non-competitive swimmers that went through three weeks of training to learn the starts, we found that the two groups reacted the same to the rear-weighted track and the grab start. This was true even though the competitive swimmers were faster off the blocks and had faster velocities than the non-competitive swimmers.

Using the data in our initial study and force data of this study to get reaction time, movement time, propulsion time, we were able to breakdown the time on the block to various elements. This start uses hands and feet, both pushing at the same time, to give the rear-weighted track start the advantage. The swimmer can push on the block longer than in the other starts and, as a result, just like in the Welcher study that was based on kinematics, we found that the rear-weighted track start generated greater take off velocity than the other starts. And somewhat like the Welcher study, we found no differences in time to 5 meters, but unlike the Welcher study, we also found no statistically significant differences in velocity at 5 meters.

The problem is that after we ran all the statistics and we were in the process of collecting data on the men, I discovered a design flaw related to the hand forces. We are going to correct this and recollect data even on the women. This is because, even though the foot forces were correct, there was an inner and outer hand forces action between the horizontal and the vertical that we couldn’t eliminate even though we think we can measure the overall hand forces correctly. We have trouble breaking them up into which is vertical and which is horizontal so that is forcing us to redesign the hand bars; and, since the hand forces are part of the overall calculation of take off velocity, we believe that this will still be true, but we are not sure until we get the overall new design perfected

Now, I think I have an explanation or at least part of an explanation as to why the velocity at 5 meters was not different even though the swimmers appeared to get off the blocks faster. We believe that when we combined competitive swimmers and non-competitive swimmers into one group, there was enough variation in terms of how they entered the water and how they glided through the water, that even though the actual velocities were numerically higher for the rear-weighted track start, we couldn’t find the statistical difference.

After talking to Joel Stagger this morning, I believe that it is possible that another design issue has to do our having all our swimmers dive into a diving pool. That decision was part of securing permission from the Human Subjects Committee. If you have to convince committee that the swimmers are not going to hit their head on anything they ask if it can be done in the diving pool? Of course, it is 18 feet deep. It turns out that that may have confounded the issue by allowing swimmers to go deeper than they normally would so we are going to be thinking about this as well. We may be moving it to a shallower pool.

In general, these preliminary data for the second study, and when combined with the first study, may support the superiority of the rear-weighted track start over the other starts. I do want to caution you that this doesn’t say that every single person should use the rear-weighted track start. Some of the subjects were clearly better with the grab start than others. It is just that when you collectively look at all the data together, the rear weighted track start is the better start.

Now, the question is, why does the rear-weighted track start appear to have an advantage? We already mentioned the bilateral deficit issue. What I didn’t mention so far is that the bilateral deficit can be overcome. Please recall the previous example of doing leg presses with two legs together and lifting 200 pounds. On the leg press where you push one leg just before the other such that it starts out as one leg pushing and then the other one joins with it to press, you can now lift 220 pounds. This is the same thing that you could lift by doing two legs or the sum of two separate legs.

One of my co-investigators, Peter Vent did just that for his dissertation in a vertical jump task and a leg press task and it turns out that you can trick the brain into thinking that you have two separate legs doing separate things. If you initiate the legs slightly asynchronously and if you think about it in the context of a vertical jump when people are like volleyball players, you will see them plant one leg and then the other and then go up where they have boom – boom before they jump. It appears to be giving you the ability to jump higher. So considering that as a background where you can have non-simultaneous initiation of forces, we thought that we could look at the forces within the swimming starts to see if there is non-simultaneous initiation between the back leg and the front leg and because we have confidence in all of our foot forces.

We looked at that and discovered that they start pushing at almost the exact same time. The hands start pulling, the feet start pushing all at about the same time. They rise up in forces so our idea that this non-simultaneous initiation may be contributing to the track start appears to be incorrect and the answer is still cloudy.

So, how is it that you can push off one foot for a good portion of this start and still be able to get off the block faster? This is, I think, the secret, and it is not just our study but another study from Australia in 2002. The rear-weighted track start was the only one that allowed the hands to do anything substantial. So it appears to be because of the hands. Leaning back allows the hands to do much more in a rear-weighted track start than in a front-weighted track start or a grab start and so it may have nothing to do with the bilateral deficit. It might have to do just with hand forces.

Now before I close, let me give you some of my personal experience with this topic. I am a breaststroker, I still swim master’s, and I competed in the 2006 World Championships at Stanford. Before I began this research, I had never done a track start in my own swimming. I don’t get on the blocks that much because I don’t compete that much, but because I was to be a speaker at a sports medicine conference at Stanford, I thought I really should get in the pool a little more, try the starts, train for a couple of months, and compete. I thought I should take some of the research and put it into practice. I spent my much of my life doing a conventional start with the arm swing, but I haven’t been doing that for the 25-30 years since I learned about the grab start. I never really felt comfortable with the grab start, either. I felt l had to do it because I would look silly doing anything else so I did it and, yet, this summer I thought I’d try the front-weighted track start and the rear-weighted track start, but neither one felt right to me. What felt right to me was somewhere in between. I don’t have a front-weighted track start, I don’t have a rear-weighted track start, I have a middle of the road track start that is just enough to provide large hand forces. I can feel where I want to be on that start so I can get a really good pull with my hands.

Thus, it is possible that these definitions of rear-weighted and front-weighted track starts are artificial and that there is a continuum of starts in which each swimmer has to find the optimum combination of leaning back and leaning forward. Therefore, you should have a given swimmer practice not just track starts, but also practice this half-way forward, half-way back position. It was very clear to me. I didn’t feel right leaning all the way back and I definitely didn’t feel right leaning to the front –and, it worked very well.

And with that I want to thank USA Swimming again for their grant support and thank you for all of your attention. I will be glad to answer any questions that you might have.

Q & A

Question: Does the body structure and an individual person’s anatomy affect speed? I would say definitely so, but we don’t know enough yet. We are just beginning to scratch the surface as to exactly which start is best and why. I think that it would be dangerous to force one start on a swimmer who might not have the right kind of body for it.

Question: Did we take into consideration the actual muscle fiber type makeup of our subjects? Absolutely not. No, that would be somebody with fast twitch muscle fibers compared to slow twitch muscle fibers. There might be a relationship to which start is best. With track and field runners yeah, right. So, you are saying that in track and field athletes, research has shown that there are definite differences between fast twitch fiber makeup and slow twitch fiber makeup in terms of speed off the blocks in the track start. But, did it influence the techniques that they used? In other words , because as you know, there are long gaited starts where the feet can be different distances, right? So, I think that would be another line of research. To see if there is some kind of relationship between muscle fiber compositions and preferred or best starting techniques.

Question: We just measured horizontal velocity, not the angle. That is part of the timing and the reaction time is built in. We have total confidence in the rising of the forces; we just don’t have confidence in the components of the hand forces yet, until we start with a new design, but the actual rise of the hand forces and the rise of the leg forces occurred almost simultaneously. In other words in the grab start of the front weighted track start the swimmers might not be pre-tensing to get the arms on there. We didn’t control for that and leg length would definitely affect that. Because in our design the hand bars so far down, we found that some people who don’t have long arms or have limited hamstring flexibility were really struggling to reach way down to grab them.

Question: That is an interesting idea. There are specially designed starting blocks that have hand rails on the side. Well, it turns out that on a track start it is not cumbersome at all because there is a lot of space to grab with your hands. Now, in a research study, we have to create new space because we don’t want to have the hands mixed up with the feet. But, on an actual starting block, with no special additions, you have a lot of space because there is only one foot to worry about in a track start and it turns out you have a lot of variation as to where to put it. Doing it myself, it felt very comfortable to pull from the front. I have never thought of pulling from the side before, but you were mentioning rails. There are a couple of studies that actually looked at rails where, instead of leaning back, if you have a rail on the side you can lean really, really far forward to where because you are holding back with the rail your center of gravity can actually be in front of your feet, but it turns out that there was no overall advantage. You got off the block faster, but you couldn’t push as hard for as long a time so you had less speed getting off the block and it was not an advantage.

Thank you very much for coming.

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