Joel Stager attended the University of Miami in Coral Gables, Florida, where he received a B.S. degree in 1975 with a major in biology and a minor in chemistry. While at Miami, he was a record holder in intramural athletics and was a competitive swimmer specializing in freestyle sprints. Dr. Stager was recruited by Doc Counsilman to Indiana University and completed his doctorate within the Medical Science Program in physiology with a minor in biochemistry. During this time he was fortunate to interact with Dr. Sid Robinson, a pioneer in the field of exercise physiology. Dr. Stager also worked as an assistant for Doc Counsilman during the summers and thereby maintained active involvement with competitive swimming. In 1984, Dr. Stager was extended an opportunity to return to Indiana University where he is now the Director of the Human Performance Laboratories. His research interests center on cardiopulmonary performance during exercise in elite athletes, exercise and environmental stress, and exercise and its effect upon growth and development. Dr. Stager has served as an editor-in-chief for ASCA’s Journal of Swimming Research and as a research advisor to USA Swimming. USOC has funded Dr. Stager to conduct projects related to competitive swimming as well as track and field. He currently oversees one of the largest and most respected graduate programs in exercise physiology in the United States. Dr. Stager is an aging “age-grouper,” was the U.S. Masters National Champion in his age group in the 50-yard freestyle for 1998, and currently helps coach the IU Masters Swim Club.
This Transcript prepared by Dr. Stager with the help of J.C. White.
Swim velocity, resistance, and metabolic rate
To begin, we know that as swim velocity increases the resistive forces (or drag forces) increase as well. This is not new information… but it is important in the understanding of what determines swim velocity. The relationship between velocity and resistance is not linear, rather, as swim velocity increases the resistive or “drag” forces increase disproportionately (Figure 1 shows a classic curve with swim velocity on the X-axis and swim resistance on the Y-axis). We know that swimming at any given velocity is basically related to the ability to generate the necessary propulsion to match these resistive forces (on the y axis in figure 1). When propulsion increases, the metabolic costs increase proportionally.
When we run or cycle, as our velocity increases the metabolic costs increase proportionately. While swimming, however, the metabolic increase, similar to the increase in drag, is disproportionately large relative to the increase in velocity. Because there is a curvilinear relationship between velocity and drag (drag is roughly proportional to velocity squared), there is also a similar relationship observed between swim velocity and metabolic rate.
When swimmers approach a velocity of 2 meters a second, figure 1 suggests that in order to swim just a little bit faster the metabolic requirement is increasing very fast – a lot faster than the velocity. This is, to repeat, because swim propulsion must go up to match the increase in resistance. Propulsion requires muscular effort and thus with an increased muscular effort comes an increase in metabolic rate to fuel the increased muscular work. The point then is this: limitations to sprint swim velocity (velocities approaching 2 m per sec) are related to the amount of resistance generated by the swimmer, the amount of propulsion the swimmer can maximally generate and the metabolic capacity of the swimmer.
Now, I have circled a data point on the graph in order to make a further comment. The data point in the circle represents one individual’s maximum power and maximum velocity. This particular individual currently cannot swim at 2 meters per second because he or she is unable to overcome the resistance, or drag, required to swim at that velocity. This represents a limit and it will impede this particular individual from swimming any faster (without appropriate coaching and training). We need to discuss the options that are available to the swimmer and coach in order to help this swimmer overcome these limitations. But first we need to figure out what the limitation is and then decide how best to overcome it.
In order to discuss the limitations, we must talk about the type of effort which we are talking about. The limitations we are observing are at a maximal effort without any form of pacing or conservation of energy. For a male sprinter this occurs at around 2 meters per second of free swimming velocity. If this effort were to be sustained for 50 m, that would equate to a swim faster than 25 seconds (when we take into account the start). We are not considering the limitations to a swim that requires pacing or a significant aerobic contribution to energy production.
Limits to sprint swim performance
So far, we have agreed that there is a propulsive component in swimming and there is a related resistive component. Either component can be the limiting factor. In each category, there are some distinct mechanisms. Propulsive power can be broken down into four mechanistic limiting factors: metabolic capacity, muscle characteristics, neuromotor function, and stroke technique. Resistance is composed of only two limiting characteristics: body size/shape/buoyancy and stroke technique. Let’s begin by talking about the limiting factors to propulsive power.
1) Metabolic capacity: Initially, let us focus upon the propulsive component. The propulsive component of swimming is going to be limited by the biochemical capacity of the muscles to produce metabolic energy as well as purely the amount of muscle mass. The demand for metabolic power is very high and the capacity to sustain this high output is very short. This can be broken down a little further by stating that during a sprint, the fuel used to generate energy for propulsion is intramuscular in origin. The metabolic capacity for short sprint events is not limited to any great extent by the cardiovascular or pulmonary systems. Extensive endurance training for sprinters may aid recovery from a sprint and thus increase the capacity to train at sprint speeds. However, it may also suppress explosive sprint power. Force production and contractility speeds of fibers are reduced with extensive endurance training.
The bad news is that the intracellular metabolic capacity for these explosive sprint events is very modestly trainable. We know that the metabolic output during these short sprints is very high and of very short endurance. Immediate peak energy sources may last less than 10 seconds at peak power output. Physiologists estimate that the ability to increase the anaerobic biochemical capacity may be less than a factor of 2. In other words – you might be able to maximally double the capacity of the sprint energy pathways during a rigorous training program. A portion of this increase comes from simply increasing muscle mass.
To put this into context then, if we compare this increase to the ability to increase mitochondrial aerobic capacity (which can increase 8 to 12 fold with training), the difference is 400-600%. It is much easier to train the muscles to increase aerobic metabolic capacity than anaerobic capacity and the extent of the training induced improvement is much greater for the aerobic energy pathway as well.
2: Muscle characteristics: The ability of a swimmer to generate mechanical force is related to muscle anatomy and muscle fiber contractile traits. One additional component of force is mechanical advantage, which may be related to body size and certain body dimensions. This is going to be discussed later in a slightly different context. In the mean time, the mechanical force that a muscle can generate is known to be related to muscle mass, muscle cross sectional area and the contractile traits of the muscle fibers. Physiologists have characterized muscle fiber types: Type I fibers, Type II fibers, red, white, fast twitch, slow twitch, IIA, IIB, IIX etc. We don’t have time or space to review all these fiber traits here. Suffice it to say that fiber type is important when evaluating and enhancing elite sprint performance. Sprinters tend to have a high proportion of fast Type II fibers that are easily fatigued, but generate considerable power. Fiber type is not a trait that is trainable. Training can cause adaptations in muscle fibers which make them more similar to other fiber types, but they can not actually change type. Furthermore, this adaptation has a very limited capacity to cause slow twitch fibers to mimic fast twitch, but a much more marked ability to cause the opposite. In this regards sprinters are born, not developed. It is true that pure sprinters are rare just as it is true that outstanding distance swimmers are rare. Correlates of fiber type include performance on the two-hand chest pass and vertical jump. In any event, specific contractile characteristics of the muscles play a role in terms of the ability of the muscle to generate power and or sustain muscular force.
3: Neuro-motor function: The third element here, in terms of a swimmer’s ability to sprint, generate high mechanical force, and great power output is ‘motor control’. Motor control has more to do with the central nervous system (CNS) than it does with the muscles. The CNS efferents (nerves leaving the CNS) initiate muscular contraction and act to enhance or suppress muscular force as need be. The central nervous system must integrate the signals coming back from the periphery and dictate the demand for force and power. Part of this is conscious but much is subconscious and filtered or fine tuned at the level of the cerebellum and spinal cord. In certain cases such as chronic fatigue or overtraining, there may be nothing wrong with the ability of the muscle to generate force. Rather, it is the ability of the CNS to initiate the demand that may be impaired. It is as if the gain of the system is damped by the general CNS fatigue of the swimmer. The effects of a taper may be to a large extent related to the recovery of the CNS from the season long extensive training. Enhancing the output of the CNS, in terms of power production, may be critical in sprint training. To emphasize the importance of the CNS we can look at the research which suggests that muscle fiber type may be less inherent to the muscle itself, but more to the nerves innervating that fiber. If nerves from fast twitch muscles are connected to slow twitch muscle fibers (or vice versa), the muscle fiber will actually switch types.
- Stroke technique: The ability to effectively apply the resultant mechanical forces (generated by muscular contraction) to the water and generate forward motion is one part of what coaches refer to as ‘stroke technique’. Doc Counsilman used to describe swimmers as ‘motor geniuses’ or ‘motor morons’ dependant upon their ability to make subtle changes in their stroke techniques. Helping athletes recognize and make these changes is the all-important coaching interface. To swim at 2 m per second, propulsive stroke technique must be optimized.
Now let’s shift gears and consider our two factors that limit resistance, anatomical characteristics and technique.
- Anatomical characteristics: One of the major factors affecting the resistive forces against an object moving through water is the cross sectional front area, essentially the size of the object that is facing the direction of motion. For humans the cross sectional area is determined by a number of things including body size, body shape, body orientation (which falls more under stroke technique), and buoyancy (which is affected by both body composition and the volume of air in the lungs). This area has been studied quite a bit and is another talk entirely, so we are going to lightly graze over it.
- Stroke technique: Stroke technique and streamlining technique that decrease resistance are important elements in swimming fast. This is important particularly in sprinting because, again, the faster you go, the greater the drag. Subtle postural or streamline changes that act to reduce resistance are important. Actually, in this context all drag is important and eliminating drag is critical to a sprinter’s success. For the moment, please accept that reducing resistance acts to enhance sprint performance given that power output is optimized. It is also important to emphasize that a swimmer can have good propulsive technique and bad resistive technique or vice versa. These two types of technique are in many ways independent, but obviously will affect one another since at certain times during the stroke they may place different demands on the body simultaneously.
To briefly summarize, sprint training begins with recognizing inherent traits and muscle characteristics in talented individuals. The training must then be targeted at increasing muscular power both metabolically and through the central nervous system, enhancing the application of this muscular power through improvements in stroke technique, and finally by reducing resistive drag force through improvements in stroke technique. The question you might have for me is; “How do I do all this?”
Strength, power and swim performance.
Central points – the first issue we have to clarify is the difference between strength and power. These are two terms that we tend to use interchangeably and we probably shouldn’t. First we need to collectively agree that strength and power are qualitatively different. I know physiologists confuse the terms and I know coaches also use the words interchangeably. We probably shouldn’t– in fact – we should be very careful when we talk about dry land training, strength training and power training because actually, these are likely to be three different things.
We are here, then, to explore the relationship between strength, power and swim performance. Once this is done, we can decide which is most important in terms of sprint swimming, strength or power. Once we can agree on definitions, – we need to discuss 1) how to measure strength and power, and 2) what the correlates of sprint swimming are. We can then ask other questions, such as; “Are there differences between boys/girls, men and women, etc. in terms of importance of strength and power?” And lastly, we can discuss how a coach can improve swim power and whether or not swim performance is likewise going to be improved?
What is strength? Strength, essentially is the ability to generate force. It’s the ability of the collective physiological system, arm, leg, upper body, to generate force. A pressure exerted upon an object without any displacement of the object is a valid measure of strength. Strength requires no displacement of mass and there is no element of time involved. Maximum strength measures are commonly generated ‘isometrically’. The joint angles are not necessarily changing and there need not be any external shortening of the muscle. Again, strength is defined simply as the ability to generate muscular force.
Next let’s consider the term “work”. In order to do work, in the physics sense of the word, a mass has to be displaced a distance against a certain force whether it be gravity, drag, or even the efforts of another individual for example. To do a lot of ‘work’ generally requires a lot of strength, no doubt. Strength then is often measured and defined as how much weight someone can lift and thus, work and strength are often seen as interchangeable qualities. Someone who is very strong can do a lot of work. However, work, as with strength, has no element of time associated with it. The amount of work done could take minutes or days and not be different. Lifting a weight 3 feet in an hour results in the same total work done as lifting the weight in a few seconds.
Power can be defined as a force exerted over a certain distance per unit time or how fast ‘work’ is done. In essence, distance per unit time is the same as velocity. Thus, power has a time element, or, it can be said to incorporate a velocity whereas strength does not. Using a physics definition, power is equal to work divided by time or force multiplied by velocity. The importance of this perspective is that swimming fast involves displacing the body against the resistive forces of the water at a high velocity. Nevertheless, it is clear that velocity is a component of power, and not of strength (except so much as strength influences power).
Recapping then, strength can be said to be the ability of a muscle to generate a force. We have previously observed that the force that a muscle can generate is related to amount of muscle mass. Actually, it is the cross-sectional area of the muscle that is critical in terms of the muscle’s ability to generate a force. If everything else is equal, the greater the cross sectional area, the greater the force that can be generated by the muscle. However, when a muscle contracts, not all of the fibers within the muscle are actually used. It is the ability of the central nervous system to recruit muscle fibers to contract, as well as the cross sectional area of the muscle fibers that together act to set an upper limit of the force a muscle can generate. It is important to remember that the two components, then, that limit both strength and power, are the skeletal muscles and the central nervous system.
To emphasize this, when an athlete is first engaged in either a dryland or “in water” training program, the initial improvements that occur – in terms of either strength or power, are central nervous system mediated. This is because almost immediately, improvements are evident with as much as a 15% improvement occuring within a week. No changes in muscle mass are observable and thus the improvements are not peripheral tissue mediated but due to central nervous system effects. It is important to remember that the CNS plays an important role in both strength and power. Fatigue can affect both the skeletal muscles and the CNS. The final outcome in either case is a loss of strength and or a loss of power.
Strength and power in isolated muscles.
Figure 2 illustrates the relationship between the force and power that can be maximally generated by an isolated muscle. On the X axis force (or tension) begins at zero at the origin and increases to some maximal value on the right. On the Y axis is the shortening velocity of the muscle with zero at the origin and some maximal velocity at the top.
Figure 2 on next page
The graph shows that when there is zero force the muscle upon contraction can develop peak velocity, but because the tension developed is zero there is no power generated. The muscle must generate force at some velocity in order to have power. On the right hand side of the graph there is a high force being generated, but because there is zero velocity, again there is no power. The big blue arrow on the right hand corner says strength, or the maximum force generated occurs where there is essentially zero shortening velocity. The point to be made here is that maximum forces are generated at minimal shortening velocities. On the left side – again, it can be seen that in order to achieve high velocity the tension must be low. The maximum power is generated at about 1/3 of the maximum force that the muscle can generate. Perhaps more importantly – maximum power occurs at about 50-60% of that maximum shortening velocity!
Both of these factors are going to become important later when we discuss optimal training. Other research suggests that in order to train for power the muscles must be trained at certain proportions of max rather than at max force production. A decision must be made about training for strength or for power.
Figure 3 on next page
Figure 3 adds another two lines to the curve. The question is, does this graph tell us anything at all about the relationship between strength and power? Most coaches believe that dry land strength measures should be related to power measures. This graph demonstrated that – yes they should be related. Even though it is hard to show strength being related to swim velocity. If a training program increases the maximum force a muscle can generate it will have the effect of shifting the curve. The red line is further to the right and thus, the maximum force that can be generated is greater. As well, at any given force, the shortening velocity is higher. Because this is so, it would appear that if strength is increased, the power at any given muscular tension is also increased.
To extend this a bit further, let’s consider for a moment the importance of morphology or mechanical advantage. If we look at figure 4 it is easy to see that the further away you are from the axis or pivot point, the higher the velocity at any given rate of shortening. In other words, the travel distance per unit time (or the velocity) is greater the further out you are from the pivot. There are two points to be made here. One, if strength increases, shortening velocity increases at any given tension. This impacts power, perhaps hand displacement and even velocity. And two, this effect will be greater the farther you are from the pivot point. Arms moving at the same angular velocity will generate a higher hand displacement the further out that hand is from the elbow for instance. It shouldn’t be a surprise to find out that most of our national and international class sprinters now are taller than in years past perhaps because of this advantage. The question now is, are there any ways for us to measure power and forces during swimming which would let us test to see if any of this is applicable.
Figure 4 on next page
Twenty years or so ago Dr. David Costill at Ball State described a way of measuring force and power while swimming by attaching a tether to a swimmer. He had swimmers swim against this tether and by so doing he carefully controlled their velocity. Figure 4 shows on the left hand side swim velocities of .2 meters per second and on the right hand side velocities approaching 2 meters a second. The swimmers swim against a set constant velocity and the force that the swimmers can generate at that velocity is measured. The dashed line illustrates the ‘excess’ forces that the swimmers generate at each velocity and the solid curve shows the resultant power that they generate at that swim velocity. Remember, this is really ‘excess’ power and ‘excess’ force at the given swim velocity and not actual power and force. The problem system is that it doesn’t allow us to look at the power or force being generated at a maximum swim velocity. At maximal swim velocity there is no ‘excess’ force or power to be measured. Everything the athlete has is going into achieving this velocity and no excess can be measured.
Nevertheless, the figure demonstrates that there is a peak value along this force-power velocity curve where ‘excess’ power starts to go down. As a means of assessing swimmers, this methodology appears to work. Changes in the athlete’s ability to generate force and or power at some submaximal velocity can be argued to be transferable. Although the model is limited because it can not actually measure maximal values at velocities we are specifically interested in, it was an important step in allowing us to think about these parameters during actual swimming.
Figure 5 demonstrates a refinement of the technique just described. In some ways, it is actually a step backward because the technology is actually much simpler. If you tether a swimmer to a stack of external weights, what will happen when the resistive load is gradual increased repetition by repetition? In other words, if the swimmer is instructed to swim across the pool as fast as he or she can and with each successive swim more weight is added to the stack, what happens to power output? Clearly, as the resistive weight increases, the velocity of the athlete is going to slow. Remembering that power is a product of force and velocity, you can see that as the resistive force increases, eventually the decline in velocity becomes greater and power output decreases. Where peak power occurs can actually be measured and identified.
A couple of useful things come out of this. We have tethered the swimmer to an external weight. We have progressively increased the load on the swimmer. We have timed the swimmer over a set distance and as a result of knowing the resistive force, we can calculate power generated against an external weight. Thus, we can conclude that this is the peak power that the swimmer can generate. We can independently measure maximum velocity (by timing the swimmer in a short sprint) and plot one against the other.
Now, our contention is, that if you do this, the appropriate training load for any given athlete, as an optimal training stimulus, can be determined. The reasoning for this is borrowed from discussions from other sports where power is important. The training stimulus employed rarely is a single maximal value, rather, some number of repetitions of a percentage of maximal load.
Figure 6 illustrates values from a portion of somewhere between 800-1,000 swimmers where these measures were obtained. We tethered them and we increased the load beyond maximal power output and then independently measured maximum velocities. We then plot maximum velocity against peak power. The resultant graph should look familiar. It is the same curve that we originally used to begin this discussion.
Essentially, figure 6 illustrates the relationship between propulsive power and swim velocity. As the ability of an athlete to swim at some maximum swim velocity increases the power needed to generate that velocity goes up as well. However, as we described earlier, the ability to generate power must go up disproportionately! This is because the resistive forces increase disproportionately. Basically, we are back to where we started, right?
We used to use the word drag instead of resistance – and it is thought that that drag is roughly equal to the velocity squared. This figure essentially demonstrates the same relationship. In order to overcome drag, a swimmer has to generate an equivalent amount of power. The amount of power needed is roughly equal to velocity squared.
It follows then that if everything else is equal, the guy or girl who generates the most power will be able to swim at the fastest velocity. Unfortunately, it is not quite this simple, because everything else is not always equal! Women cannot generally produce the same amount of power as men. Swimmers differ in the amount of form drag they generate. Not all swimmers apply the forces they can generate optimally.
There is some debate in the literature as to whether this is a linear relationship or whether it is an exponential or power function. That, I suppose is for the biomechanists to debate. In terms of the practical extension of this research, the tethering device we used is just a stack of weights with several pulleys at the top. The curve that we have drawn (figure 7) below basically shows the data from a one athlete. We know that each plate on our stack is equal to about 2 Newton’s. We increase the load that the swimmer has to swim against in a step wise manner and then we calculate the power by recording the time it takes them to swim 10 meters. We do not include a push off and only record a straight swim. When we plot the power against the number of plates to generate that power we can show in increase up to a point and then a decline. The stack of weights we use has I think 30 plates and we have the option of adding two more heavy plates that will allow us to “see” another 20 steps if we so choose.
The weight stacks we used are available thought TPI in Ohio and are marketed as “Power Racks”. But in order for the system to work as we wanted, we had to make a number of modifications. Jerden Industries in Bloomington IN made these modifications for us. The first thing that they did was to increase the travel distance to 25 yards. The standard “Power rack” only goes about 11 yards. What we needed to do was to eliminate the push off and the breakout from our measurements so that we could time a clean 10 meters. I should emphasize that this protocol is not something that we developed – it was originally developed by Hopper in the early 1980s. In order to increase the swim distance, we had to change the mechanical advantage and this actually had an additional effect of also increasing the sensitivity. Each plate we added made less of an effect. On top of the new top weight stack is a big pulley and these big pulleys increase the mechanical advantage to somewhere around 10:1. The over all effect is that we now have more steps with smaller increments at a longer travel distance when compared to a standard “Power Rack”.
Coaching Power Training
The missing ingredient when we first started using this protocol was ‘time’. Swimmers always wanted to know how fast should they go. What is a good time? What we found out was that the 15 yard time or the flag to flag time is essentially the goal time. That is, when you calculate the swim time at which peak power is measured, it is equivalent to the swimmers’ ‘flag to flag time’ in a 25 yard pool. In other words, now we know what their training load should be and we also know what the swimmers’ goal time should be for the 10 tethered meters.
Referring to figure 8, there are two swimmers circled who measure out with essentially the same peak power. The question is, if they are generating the same power, why aren’t they able to attain the same swim velocity? From the coaching perspective, you need to ask if both swimmers are limited by the same parameters as far as maximal swim velocity is concerned? And if not, how do I coach these two swimmers differently to promote increases in each swimmer’s maximum velocity? The swimmer on the right is actually on the ‘best fit’ line described by all of the swimmers. He is basically doing what we are saying the average swimmer does. The swimmer on the left, however, is not so, and there must be more to that story.
There are a number of things that can be done with this equipment if you have the time and are so inclined. You can count the number of strokes these athletes are doing over the 10 meters and divide that into the power generated, and by doing so, power per stroke can be calculated. Our results suggest that the nature of this relationship is stronger than that between power and velocity. The correlation coefficients approach 0.9 which means that we are accounting for nearly 80% of the variance among all of our sprinters. I realize that this may or may not be terribly surprising to coaches. The data show that it is not how many strokes can you take in 10 meters that is important. It is how much power you can generate per stroke in 10 meters. The swimmer who is taking the most strokes doesn’t necessarily win the race. Some recognition must be made that distance per stroke plays an important role. That is an important concept for both swimmers and coaches to recognize.
The other thing that can be incorporated into this paradigm is tempo. If a coach knows what race tempo is, if you have taken their tempo from a competition, for example, you can incorporate tempo into these training bouts. Assuming now that you are timing the swimmer for 10 meters, counting strokes and measuring power, you have the data to calculate stroke frequency and distance per stoke. You can now tell the athlete exactly what you expect of them during any given training bout on the rack. However, with this approach, the coach plays an integral role and sending an athlete over to the rack for a workout on their own is probably less than optimal.
As a researcher I spend much of my time defending my position and approach and I realize that as coaches, you are not particularly interested in the nitty-gritty behind the scientific scene. Your interest is primarily how to make your swimmers faster. I feel as if I need to take a short aside at this point to indicate that we didn’t necessarily start out to measure these specific variables. We measured ‘a whole lot of other things’ at first, but it turned out that ‘a whole lot of other things’ didn’t appear to us to make much difference in terms of explaining the differences among sprinters. We began by measuring a large number of variables and assessing a large number of swimmers. We ran statistics on them and basically came out with what you have already seen, that power and power per stroke are important determinants of sprint swim velocity. Table 1 provides data for some of the variables for which we have data. This is about a third of the number of variables we have measured. It isn’t necessary to go through all of these variables individually. I am trying to convince you that, yes, we did look at certain measures of strength, for example. Yes, we did look at alternative measures of muscular power for example. Yes, we did look at other parameters that previous researchers thought were important dry land correlates of performance. The process is to collect this data and then run correlation matrices to identify the strength of the relationships among all variables. A graphic representation of this process is found in figure 9 a-d. In the upper hand corner (fig 9 a) is a graph of peak power versus maximal swim velocity. This is the relationship that we have spent considerable time on and it is a nice tight relationship with a high correlation. The next one over (fig 9b) is obtained through a second protocol, something we haven’t yet discussed. The important thing to see is that the data creating the curve is more scattered. Figure 9 c illustrates the relationship between power as measured by the two handed chest pass and swim velocity. The swimmer’s task is to see how far they can throw an 8 pound medicine ball while seated in a chair. The relationship is again, increasingly less well defined. The worst one the last figure shown (9d) and it shows the relationship between the vertical jump and swim velocity. Coaches and researchers have been talking about vertical jump for years, but in terms of assessing power in swimmers, our data suggest that it is simply not very effective.
The next figure (figure 10) illustrates several additional steps. Actually, it summarizes much of the outcomes of the research process better. Remember that the initial point of all this was to better describe the relationships which might exist between strength, power and swim performance. One working hypothesis was that muscle size, that is, cross-sectional muscle area, is an important determinant of swim velocity. While it is one of the variables we measured, unfortunately, it is a very crude estimate. The way it is obtained is by assessing triceps skin fold and circumference of the upper arm. Calculations allow the elimination of fat mass and bone mass, etc. and provide a crude estimate of upper arm muscle cross-section area. The correlation coefficient between this and swim velocity is low (0.13). Other measures of muscle strength such as 1RM lat pull or bench press etc were obtained and resulted in similar low correlations (0.21). These need to be compared to the values presented earlier for the relationship between power and swim velocity and powere per stroke and swim velocity, (nearly 0.9). How about muscle size and muscle power? One would hypothesize a relationship and there is, but not between swim power, only muscle power (r = 0.48).
When we look at swim power vs. swim velocity (and this is men and women collectively together) we had a linear correlation of r = 0.81 which is relatively high. The highest correlations we obtained were between power per stroke and maximum swim velocity.
Figure 10 next page
Muscular strength intuitively seems to be important. Earlier it was argued to be important in the isolated muscle preparation. But so far, in terms of its importance to sprint swim performance, it is hard to defend strength as an important component of maximum swim velocity. It is, however, apparent that muscular strength is related to muscular power which in turn is related to swim power. The other parameters measured, more consistent with conventional swim theory; maximum power and power per stoke, have been verified as very important determinants of maximum swim velocity. The obvious question from coaches is then, how do you develop swim power? Before answering this question, we need to look at swim power from one additional perspective.
The Swimgate Test
Another tethered test described in the literature uses a bungee cord attached to starting blocks. Swimmers are asked to swim as far out as they can away from the blocks with one maximum tethered effort. The maximum force they can generate is measured. Using this system, we cant measure swim power because when the swimmers get out towards the end of the bungee cord (and eliminate all the elasticity) there is no displacement and thus, no ‘power’. The swimmer is allowed to recover and then asked to begin at the point at which maximum force was attained. They are then asked to swim for 30 seconds. This is one of the most enjoyable experiences your swimmers can possibly have! They really love doing this test. In fact, they love doing it twice even more if the force transducer doesn’t work the first time. We look at this is as a profile of their sprint performance. In many ways unique and individual in nature, much like a metabolic fingerprint. Figure 11 reflects this 30 second maximal effort and we look at it as a window into the biochemical limits of an individual’s sprint performance.
Figure 11 next page
The limitations that are exposed here seem to be related to the metabolic power generated. The metabolic power requirement is very high at this work rate. The energy supply, primarily from the phosphagens immediately available, can only last for a very short period of time. The peak output occurs somewhere around 5 seconds into things. This ouput can not be maintained very long and within 7 or 8 seconds it is starting to come crashing down. At this point more of the energy supplied must be done so by glycolytic means. The instantaneous power output must necessarily be less. Around 20 seconds it is almost down to the low point.
From this protocol we can measure the mean force generated over 30 seconds, and a peak force. We can describe a fatigue index by looking at the slope of the curve (or the % decline from peak to the end point) and we can measure the time from the start of the test to peak force (Tpf).
If we put these parameters into terminology relevant to swimming we can now discuss training goals and positive outcomes of an optimal sprint training program. The goals that we see as important are: increasing peak force, increasing mean force, decreasing the fatigue index, and decrease the time to the maximum force.
Figure 12 has a dashed line and a solid line. The solid line represents the test performed by a swimmer at the beginning of the season and the dashed line represents the same swimmer’s post-season assessment. The arrow at the top of Figure 12 indicates that the training program was successful at increasing peak force. In fact at any given time along the x axis, the same is true, force is greater. The ability to generate force is always greater and just as significant, the time to peak force went down. This is important for two reasons. The first is that the swimmers are generating more force, greater mean force, and are able to do it with less delay. You might see this as swimmers coming off the blocks and rather than building into the sprint, when they hit the water they are nearly at peak velocity from the onset. The second is that within this 30 second window, the force generated (which we see as directly analogous to power output in un-tethered swimming) is improved.
Unfortunately, what did not occur in this particular training regime was a change in the fatigue index (the slope of that line). In fact the slope is nearly identical pre to post season. This is interpreted to mean that our ability to change the rate of fatigue in an all out sprint is limited. This parameter is sometimes referred to as “sprint specific endurance”.
Mike Bottom and I spoke about this problem five or six years ago. He said, “you know what really troubles me as a sprint coach? I cant figure out how to improve sprint specific endurance. What do you think? How do you go about improving the ability to bring back a sprint? Do you think it is possible?” – Unfortunately Mike, you know what? From the data in Figure 12, I’d have to say that I don’t know how to do it either! While I didn’t describe the training program yet, the outcome suggests that the one flaw in the program is that the fatigue index didn’t improve and it may well be that this can not be done. If not, then, my best advice is that you have to coach your swimmers get out fast on the sprints. Swimmers cannot afford to ramp up into a 50 because no matter what, the slope of the line (rate of fatigue) is going to be the same. Swimmers have to have the confidence to get out fast in the sprints because in a maximal effort the rate of decline seems to be inherent. It may be representative of the metabolic limits of the muscles. Coaches that are interested in reading more about this should look into the literature that pertains to the “Wingate test”. The Wingate is usually performed on a cycle ergometer and similar to what we just described is a 30 second all out test. The discussion will be relevant to swimming even though the test may not be entirely appropriate due to it being a test of leg power.
At this point I think we should discuss the type of training that we might want to impose on our sprinters to improve swim velocity, given what we have already discussed. From the physiological prospective, base training requires 6-8 weeks. Aerobic base can be considered “the training necessary to begin to actually train.” This, clearly, is the first phase of a training program and it turns out that most of the research says that once this is accomplished you only need about two – maybe three bouts per week of intensive aerobic training ‘sets’ to maintain a swimmers aerobic base. For a sprinter, the aerobic base training is directed at recovery rather than sprint performance per se. We need to remember that for a sprinter, it is not about swimming 50 times 100. It is about swimming one 100 or one 50 as fast as you can. Nearly any aerobic training above and beyond that needed to recover will not do much more than slow the sprinter down. The reasons for this are complex but essentially, aerobic training shifts the muscle towards a metabolic pathway that is sustainable. The emphasis is upon endurance rather than power and the outcomes inconsistent with each other. Studies have shown that you compromise each trait if you train both simultaneously.
During this initial phase, it is appropriate to incorporate a rigorous dry land training program. Despite the difficulty in relating strength to swim velocity, I am not suggesting that you eliminate dry land training altogether. I am going to say realistically – if you think this is directly improving your swimmers’ performances – I cant find any evidence for it myself or in the literature. Our data would suggest that muscle mass is an important variable in muscle power output. I also believe that there is evidence that, dryland training might act to preserve shoulder health. If you cant train because of shoulder problems, you cant improve your performances. There may be a role for strength training in developing core strength. But again, – the physiologist’s cant show that that is related to maximum swim velocity. And that, of course, is our ultimate goal here.
The preliminary steps pertaining to specific sprint training begins during this time. The first step is initial testing of the swimmers to identify training load. The sprint swimmers will be prescribed with a specific sprint training protocol using the stacked weight system described earlier (Jerden Industries, Bloomington IN). Maximum swimming power and maximum swim velocity will be measured separately. The protocol (Hopper 1980) entails beginning with a few plates and then progressively adding plates until the swimmer adds three seconds to their initial time (over ten meters) or until they add 5 strokes to their stroke count. We refer to this as the ‘progressive test and will require that the athlete swim as many as fifteen maximal ten meter bouts. Some rest will be required such that fatigue does not become the primary reason swimmers fail.
There are some issues to think about before beginning on this tract. Most coaches are not going to have the time to do this kind of training with 85 swimmers in their club. Coaches will have to decide on the basis of age, physical maturity, event focus, sex etc who should and who should not be trained in this manner. This type of training can not be considered a short cut. It is very effective but also time intensive. You have to decide who is going to be on your “A sprint team”, who is going to be on your “B team” and who is going to be on your “C team”. Those on the “C team” may never do any of this type of training because it is inappropriate or not a high enough priority. Your decision will have to be based on what the swimmer’s intended training outcome is. If you have the ability to say who is going to be your 50 meter sprinter, who is going to be your 100 meter sprinter and who is going to be your 1000 swimmer you can set priorities on this basis.
There is evidence that suggests you may be wasting your time with 12 year olds when doing a lot of specific power training. It is not that they cannot improve, but it is mostly central nervous system mediated. The skeletal muscles probably don’t have much capacity at this age (particularly the boys) to increase in mass or respond otherwise. The neuro-endocrine axis is not mature. You can train them to increase swim power, but it is not peripheral in nature. Because of this, this type of training is primarily for the older physically mature swimmer. Twelve year old girls and younger and boys younger than fifteen are going to be on my “B or C teams”. Swimmers focusing on the longer events will also only do this triaining on a limited, time permitting basis.
In the second month of our season, basically what we do is we identify the tethered bout that represents maximum power output. From this we calculate an 80% load. This is going to be our ‘resisted load’ at which we begin our training. Jim Steen at Kenyon College in Ohio uses a regime where his swimmers start with 10 reps over 10 meters on a 45 second interval (at 80%). He does this three times per week, optimally. The next question at hand is, “what is the target time for the swimmer over this ten meter distance?” We found that the untethered swim time, flag to flag in a 25 yard pool is nearly perfectly correlated to the ten meter time at which maximum power is recorded. This makes life easy! We now know the optimal load and we know the optimal time. We also know that one plate on our stack results in the swimmer being slowed about 0.2 seconds. We can therefore make subtle adjustments fairly easily. Our goal is to tether the swimmer to a weight that doesn’t slow them down to the extent that stroke mechanics are changed or significant changes in tempo are evident. The point is all of this is easily measured, calculated, and adjusted.
Each time the swimmers perform on the stack their times will be recorded and their individual goal times are compared to their initial time. As their flag to flag times improve, it will be necessary to readjust the tethered load. It may take only a single bout to cause a significant improvement in 10 meter times despite other intensive training. Improvements in power output on the order of 10 to 15% have been observed in as little as a week.
The easiest way to plan a program is to start from the championship event and work backwards. We have found it to be effective to do two short bouts the final week before the championship event. The goal over the last seven or so weeks is to increase the tethered load every other training bout as long as the swimmers show continued improvement. The rest interval is increased and the number of repetitions is decreased weekly as you approach the championship event. Three weeks out, for example, the athlete might be performing only 6 repetitions at 40% more resisted load than they began with – on a 90 second rest interval. This compares to the 12 or 14 reps on 45 seconds they might have started with eight weeks earlier. For the high school students we may start 5 weeks out from the championship – do ten reps, with one minute rest. Four weeks out we increase the load by two plates (which is four newtons on our stack) but 8 reps at a minute 15 and from there we go down progressively (weekly). We will actually do a set three days before the championship. It is not fatiguing but what it does is act to remind the central nervous system and the spinal motor neurons what it takes to generate power – what it takes to “get up and go.”
Now, here are several simple recommendations as to how to organize this type of sprint training program using stacked weights. It is best to put together a note book in which every swimmer has his or her own section. We print these on waterproof paper and use pencils to add data as a means to preserve the values. At the top is the date for each workout. There is a place to indicate what the workout number is. We begin at “1” at the start of each season. We also include a line indicating who the coach was who monitored this particular workout. A priori, we list the goal time for the 10meter swims based upon the initial testing and the previous training bout. We include a row for the number of reps they are going to do in this bout. There are columns for time, number of plates, number of strokes and what stroke was done. You don’t have to limit all repetitions to freestyle. Swimmers can do freestyle, butterfly, breaststroke and or kick sets. Once you get used to collecting the numbers you might want to include another column for tempo. This is easy to calculate because the number of strokes is known and the swimmer’s time is also known. Thus, you can figure out what the swimmer’s tempo is and determine whether or not it is appropriate when compared to their tempo used during competition.
Now, before going any further, it is important once again to keep the physiology of the skeletal muscles in mind. Here are a number of important quotes from classic textbooks in physiology that are relevant to coaching sprinters. “Almost any routine activity will cause a muscle fiber to reduce its rate of shortening” “The most effective way to increase muscle fiber shortening velocity is complete inactivity.” “Endurance and other metabolic changes are much more readily changed compared to the changes involving speed.” “Repeated stimulation does increase endurance capacity, but it is not an effective means for increasing fiber size.” “Chronic low frequency stimulation, as in repeated sub-maximal bouts, is the best way to make a muscle weaker. This should be viewed as a deliberate response by the muscle becoming a metabolic machine.”
What do these quotes mean to the coach and athlete? There are two, somewhat opposing traits that can be simplistically described for skeletal muscles. They are endurance and explosive power. The limiting factors in muscular endurance are essentially metabolic. Repeat bouts of modest intensity exercise will improve the endurance capability of the muscles by enhancing the metabolic machinery for generating metabolic energy aerobically. Unfortunately, this does little to enhance maximal mechanical power. Mechanical power, as we have discussed earlier, is a function of shortening velocity and the force that can be generated. Anything that acts to reduce either of these aspects of muscular contraction will compromise the ability of the muscle to generate mechanical power. To generate mechanical power, you need to perform exercise that is explosive, near maximal, and infrequent. These are exercise bouts that either train the central nervous system to recruit fibers and or teach the CNS how to generate power. Alternatively, you might want to plan training bouts that early on, act to stimulate increases in muscle mass and only later teach the CNS how to use it.
Finally, let’s see if we can put all of this together in a summary of sorts on power training for sprint swimmers. First, it is important to recognize that power training is very fatiguing to the central nervous system. This training can be so intensive that when added to concurrent training it can actually be detrimental to performance rather than positive. Coaches tend to think, “Oh this is great. I am going have my swimmers do this three times a week and I am going to have them in the weight room an additional three times a week.” Well guess what? If you take this approach, you are going to kill your sprinters. Maybe not literally kill them, but they will certainly be unable to swim fast. This is likely because they will not be able to recover. Keep in mind that improvements occur during the recovery phase as much so as during practice per se.
It may seem hard to believe that a 7 second exercise bout performed ten times can be fatiguing. Compared to the type of training that most of the swimmers do, it certainly doesn’t seem so. It turns out that the central nervous system finds it very hard to recover from this maximal repeated effort. The coach needs to consider this and perhaps gradually ease off of weight training once the ‘in water power training’ is begun. It becomes a matter of priority. So although the skeletal muscles are not necessarily fatigued, the CNS seems to be.
Over-distance, or rather high volume, long yardage, aerobic training will eliminate or diminish the beneficial effects of power training. Sprint swimmers cannot do power and endurance training at the same time. Remember, almost any repeated prolonged activity will act to slow the muscular contractile process. Furthermore, spinal reflexes are suppressed and peripheral motor neuron activity is inhibited with high volume training. In other words, when you over-train athletes (which is standard practice in swimming), their ability to generate power is typically diminished mid- season. This appears to be mediated by the CNS and spinal cord. It is as if the ‘gain’ is turned down such that for any given motor output or any given conscious effort, the ability to generate power is lower than it was before training began. Gain might be explained as being a multiplying factor for effort. The resultant muscular output or force is equal to the gain multiplied by the requested input (effort). In other words, any given effort might be perceived as being greater if there is a low gain. When tapered, the opposite effect occurs. The ‘gain’ is set way up such that for any given effort – muscular power output is amazingly high. Equivalent performances seem nearly ‘effortless’. This seems to take place within the central nervous system as well as at the level of the spinal cord. The point being that power training is intense and all training is additive. If swimmers are engaged in high volume aerobic base training, dryland training and ‘in water’ power training, perhaps too much is simply too much. It is all additive!
One great way to think about ‘in water’ power training is as a good wine with a great meal. You shouldn’t waste it on the children and the unappreciative (for our purposes here- the unappreciative loosely refers to distance swimmers!) In the United States, we don’t commonly let our children drink wine. Society has decided it simply isn’t appropriate. So this training should be thought of as ‘good wine with a good meal.’ Select your ‘A team’. Forget the children and impose a progressive, carefully planned, power training program. But be very careful about it.
The point of having data on each swimmer is to be able to monitor the swimmers as individuals. If they can not make the goal time based upon their flag to flag time, then they are either moving towards over-training and or exhibiting general fatigue (Doc Counsilman called this ‘failure to adapt’. If you keep careful watch on the swimmers’ progression this can be easily evaluated. For example, if a swimmer attempts a repetition that was performed well the previous training day and is now 0.2 seconds slower, you may need to intervene. Your choice is to either back down on the weight so that the swimmer is able to make the goal time or give them another day to recover before attempting the set again. Swimmers need to understand that this workout is essentially ‘all out’. That is the only way this training is effective. Even so, it is typically not exhausting as each repetition only lasts 6 to 10 seconds. By having the numbers at hand you can tell immediately if the swimmer is giving it his or her all or… if you have a recovery problem. Other signals include not being able maintain their competitive tempo. Or the swimmer might add a stroke over the 10 meters which may be an early indicator of fatigue.
As the swimmers’ times on the tethered swims improve, add weight and as the season progresses towards the championship event, add more recovery time between repetitions. The stacked weights allow artificial increases in the resistance load on the swimmer and therefore the swimmer has to increase propulsive power output. However, in order to maintain this, they will need more rest between each bout. The research literature is somewhat inconsistent here. Some sources say that the immediate energy sources that are used to fuel this exercise bout can recovery nearly instantaneously and others say that this requires several minutes. Observations suggest that sprinters can not only maintain their performance on these tethered sets but in many cases they can build through out the set and get faster.
Another caution, however, pertains specifically to the guys. The boys see these weight stacks and their immediate desire is to ‘rack the stack’. Virtually 100 out of a 100 boys walk in to the pool and think that they can pull all 50 plates. There are several reasons not to do this. First, it may be detrimental to shoulder health and wellbeing. This resistance is much more than the swimmer will actually ever need to overcome while swimming. Unattended or unsupervised use of these systems can result in significant shoulder trauma. Secondly, when the resisted weight causes changes in stroke technique or tempo, it is probably doing more harm than good. The key is simulating their sprint training at race tempo, peak velocities and peak power output.
In recent studies performed in our lab, ‘in water swim power training using a stacked weight system increased power output over the course of a 12 week program 28% in high school girl swimmers. Increases were even more dramatic in the boys with a 40% increase observed. Admittedly they were they were also doing traditional swim training. I can’t get a coach to have half the team just do power training and half the team train traditionally. Coaches don’t really want to limit the study to just five or six swimmers. The point is, it weakens the experimental design and makes it hard to formulate clear-cut conclusions.
Another interesting observation from this study was that there was a different temporal response in the men and the women. The women increased their power primarily at the front end, in the first half of the season. Very little change took place beyond midway. The boys, in contrast, continued to improve through out the entire season. It may be that this is due to the fact that women have less potential to generate muscle mass and therefore less capacity to improve power. They therefore must become ‘technique specialists’. The men and boys are capable of generating more power and thus may ‘muscle’ themselves through the water rather than to move through the water through perfect technique. This relationship is something we plan to consider more carefully.
Final Conclusions: Although it can be shown to be theoretically important – strength is difficult to demonstrate as a direct determinate of sprint swim velocity. It may play a role in shoulder health and joint stability. Strength may also be related to muscular power which is related to swim power. It is difficult, however, to demonstrate the direct role of strength in sprint performance per se. Power – specifically power per stroke is seen as a primary determinant of sprint swim velocity. Fortunately, swimmers can be trained to increase swim power, power per stroke and reduce the time it takes to generate peak force (and power). This can be done without losing focus on stroke tempo and distance per stroke. Age related differences suggest that this specialized training may be appropriate after age 12 or so in girls and age 15 or so in boys. Coaches need to remember sprint swimmers are being trained to swim a short competitive event – not a two-hour endurance event. The physiological research suggests that when you train your swimmers aerobically, you may be impeding maximal power output. Specific ‘in water’ power training has been shown to be an effective means of improving swim power and sprint swim performance in both boys and girls. It is not necessarily a short cut, however, in terms of coaching supervision.
Costill, D.L., Rayfield, F., Kirwan, J., & Thomas, R. (1986). A computer based system for the measurement of force and power during front crawl swimming. Journal of Swimming Research, 2, 16-19.
Hall, S.J. (1995). Basic Biomechanics 2nd ed. Mosby-Year Book Inc, St.
Louis, MO, p. 157.