iCranks, the first second generation power meter
What is a 2nd generation power meter and what are iCranks. A first generation cycling power meter is what we are all used to, it gives the rider their power while they are riding and it collects that power for later analysis. A second generation power meter does the same thing but also is able to give and collect individual pedal force information. This can only be done when there are two power meters located in the crank, pedal, cleat, or shoe. The iCranks power meter is located in the crank arm of the basic PowerCranks. This gives the iCranks the ability to measure and display the riders pedaling technique and if we know our pedaling technique we can know our weaknesses and how to to best spend our training time to improve even further.
Before we move on let's discuss the question: What is the ideal pedal stroke? Most people think that cycling is a simple activity and we all do it pretty much the same way. We push on the downstroke and unweight/relax on the upstroke. Such a pattern ends up giving a force application pattern that resembles a sinusoidal repeating curve as we will see. The real question is, since the total power is the average power for the entire stroke, the ideal pedal stroke should be the variation in this sinusoidal pattern that results in the highest average power. Can we analyze and then modify our technique to get a higher average power? Let's see.
Let me go into more detail using some actual data. Here is an example of an iCranks screen shot.
Now, this is a little difficult to interpret so I am going to transform this polar graph to a more standard linear graph.
Looking at this data it is easy to see a couple of things right off the bat? We can see that the right leg is substantially better than the left leg, having both a higher peak down force and less negative force such that it is averaging 305 watts around the circle while the left is only averaging 266 watts, a 39 watt (13%) difference between the legs. Add them together and we find the rider is generating 571 watts, the number he would see on his power meter. The imbalance information, by itself, is important to know as athletes with substantial leg imbalances are more prone to future injury. Working on strengthening the weak leg will not only give this rider more power but will reduce risk of future injury. But, the other thing we learn is that the average around the circle depends upon two things, the height of the curve (the hardest point of the push), the amount of negatives, and the shape of the curve.
Some here might point out that 1st generation "combined torque" power meters (such as Computrainer and SRM) currently measure right left imbalances and might wonder why this is better. The answer is sometimes combined torque power meters get it completely wrong. Let's look at the above example. The way Computrainer or SRM analyze this is they look at the combined output of the two cranks and then compare the results of the pushing portion of the right and left cranks. So, what is done on the upstroke on one leg gets added or subtracted to the pushing portion of the other leg and this total is seen as the output of that leg. The fact that the left leg is substantially weaker on the upstroke than the right leg means this will make the pushing portion of the right leg look weaker than it is, making the rider appear more balanced than he is. Only when the back stroke portions are equal will this analysis reflect reality. But, in the above case, a combined analysis, such as done by Computrainer or SRM, would show the left to be 295 watts and the right 276 watts, a difference of 6.5%, distorting reality and making the rider appear much more balanced than he is. Here is another real world example, a rider whose right leg pushes harder than the left.
But, in this instance, we find the right, stronger pushing (646 vs 633 watts), leg is also weaker on the upstroke (-167 vs -97 watts) and this combination actually makes the right leg less powerful overall despite pushing harder. While this isn't the exact same analysis as the previous case it would appear that if we were to combine the right and left crank torques then the total for the "right" leg (646 - 67 = 579) suddenly becomes greater than the left (633 - 166 = 467). In this instance, the actual situation is the right leg is 18.4 watts (11%) weaker in total power but the combined torque analysis would tell the rider the right leg is substantially stronger, completely backwards. Working on strengthening the "weak" leg in this situation would only make the situation worse. It is clear that what happens on the back portion of the pedal stroke determines how close to reality a combined torque analysis is. This is explained in more detail in the book High-Tech Cycling by Ed Burke, an excerpt is available here. Unfortunately, the only way to know what is going on during the back portion of the pedal stroke is to measure it (or to use PowerCranks where we know minimum torques never go below zero).
But, how can we use this information to actually improve?
We now know that the iCranks gives superior information regarding imbalances but I know you are asking the question: "What else can we learn to help us to increase the average beyond simply pushing harder?" Back to the first rider. One obvious thing he could do would be to just to eliminate the negative forces from his current pattern. Simply eliminating the negative forces from the pedaling circle would improve the right crank power from 305 to 324 watts and the left crank power from 266 to 296 watts. By making this simple change alone he would improve his power from 571 to 620 watts, a 49 watt improvement. And, if he could make the weak leg the same as the strong leg he would gain another 28 watts, giving him a total improvement of 77 watts, a more than a 10% improvement!
Not bad, but can more be done? Since we are looking for improvements that could increase the average let's look at the shape of the curve. We can see he is much stronger coming across the bottom than coming across the top. Let's see what happens if the rider can become symmetrical around the maximum push point and eliminate the negative and see what such a pattern might do to the power numbers.
By simply balancing the legs, making him work as much before the maximum as he does after and eliminating the negative forces, without pushing one ounce harder, here is what happens.
WOW! Each leg would now be putting out 364 watts or the rider would be at 728 watts total, a 27% increase from 571 watts he was doing before and all without pushing one ounce harder. It is clear that broadening the force application has the potential to greatly increase overall power. Let's see what happens if we broaden it more, to a pure sinusoidal pattern
This pattern, when we combine the two legs together, almost doubles this rider's power from the 571 watts he was doing to 1002 Watts! WOW!, again. It is now clear, the pedaling technique issues dramatically limiting the power this rider was seeing were two, he was losing about 50 watts from the negative forces on the pedals during the upstroke. But, more importantly, he was losing even more power because he was doing essentially no work accross the top. It is not really possible to diagnose the degree of this deficiency without the information obtained from a 2nd generation power meter. It wouldn't matter if this rider were putting out 100 watts or 1,000 watts, broadening the shape of the power curve will increase the average power for one revolution compared to the peak pushing power. Trying to increase the portion of the pedal circle in which substantial force is applied will result in power and efficiency improvements. This is what we mean when we say we want you to be "pedaling in circles".
I have been talking theoretical improvements here. How much broadening is possible in the real world is yet to be determined but, I suspect, it is a lot. At least now, we have the ability to measure this.
Is there scientific support for these thoughts?
Is there scientific support for these musings? YES! In 2011, Leirdal, et. al. demonstrated that the only component of the pedaling stroke they could find that correlated to improved pedaling efficiency was the size of the forces across the top and the bottom of the stroke. In addition, Lutrell and Potteiger in 2003, also showed that training with PowerCranks improved pedaling efficiency. Even though Lutrell did not measure pedal forces we do know that one of the results of training with Power Cranks is improved activation over the top and bottom of the stroke and we can infer from the Leirdal results that these are related.
Since any second generation power meter should be able to measure these forces and help the rider understand their technique the question now becomes: "How does one achieve these changes?" Now we are getting to the real value of the iCranks because they are incorporated into the crank arms of PowerCranks and broadening the stroke and eliminating the negatives are the normal changes we expect to see when cyclists train with PowerCranks. The graph below illustrates the actual form changes measured in one rider after 3 months training with PowerCranks compared to the above "ideal".
Notice the rider has seen a broadening of the power application and the negatives have been eliminated, a change that computes to a 35% power increase if the max pushing force were kept the same. With a 2nd gen power meter we should now be able to follow these changes but, what we can also learn from this data is that this rider has even more potential he should be able to achieve by concentrating on even further broadening the "power application" part of the stroke (coming over the top is still the weakest part of the stroke) and not worrying so much about "pulling up" on the back stroke.
But, how to broaden it even more, more than the usual training techniques (including PowerCranks) can provide? We can apply the training principle of "overload" training, all we need do is add additional resistance (overload) to moving the pedals beyond what the bike provides at the top and bottom of the stroke then the rider can eventually train both the muscles and the nervous system to be better at doing this. Here is one method I have devised that can be used in conjunction with the PowerCranks.
All I have done is attach bungie cords to the pedals that apply resistance in the direction we are trying to improve (in this case, over the top). If the bike had regular cranks I would have to put one of these cords in front or the resistances would cancel each other out, since the cranks are connected and at 180º. The amount of resistance is easily increased or decreased per the capabilities of the rider and the amount of overload desired. In addition, we can add resistance to essentially any part of the stroke by moving the bungie cords to the front or up and down. And, if we have a 2nd generation power meter we can measure the effectiveness of our efforts with serial testing with the bungie cords gone. I have even designed a similar system that could be mounted to a training bike and taken on the road since the key to effecting this change is time in the saddle working against these increased resistances.
While this looks silly the intent here is to make it possible for the serious athlete to get as much time in the saddle as possible working on these hard to train parts of the stroke. It is called overload training, forcing yourself to do more than you would normally do until doing more than you are doing now becomes natural. It is the same as interval training except we are looking to improve technique instead of overall fitness. If this were done I believe the serious cyclist could attain power and efficiency levels unimaginable now, the only question being, what is the limit?
So, what happens in the real world. What do world class cyclists do now? Here is a video demonstration of the TA (torque analysis) tool of the iCranks showing the pedaling technique of Olympic cycling champion Sara Carrigan doing a ramp test. What can we learn from this?
1. Notice that the negative forces she had on the backstroke at low power got smaller and smaller as she increased power, to the point of becoming zero. Most of the increased work when she increased power was done on the backstroke.
2. She is doing essentially no work across the top. If she could learn to do as much work across the top as she does across the bottom she could generate substantially more power than she does now. The only question is how much improvement is possible by making this change, discussed next.
What might the limit be?
This is the real question. All this theory but what will happen in the real world. We really do not know until we start to see how people respond to this training. In general, most people think we are limited by our cardio-pulmonary system, usually tested as VO2 max. But, exactly what is that limit? Some people have tested very high (in the 90's) and how high one tests generally corresponds with how hard they have trained aerobic endurance and how many muscles they are using - rowers testing higher than cyclists testing higher than ping-pong players. The heart generally adapts to chronic stresses presented to it. Broadening the pedal forces involves using more muscles so we would expect that VO2 max for any athlete learning this technique would increase (demonstrated after PowerCranks training in a university study done by Dixon). But, it takes many years for the cardio-pulmonary system to fully adapt to these increased stresses so how much improvement in VO2 max is possible is unknown. It certainly will depend upon where the athlete is starting and how hard and how long they work. While we have suggested in the above analysis a doubling of power is possible I doubt a doubling of VO2max is possible, therefore it is reasonable to doubt the "doubling" hypothesis. But, wait, power also depends on efficiency (the amount of power per molecule of oxygen consumed). Leirdal demonstrated that efficiency correlated most closely with forces across the top. It is reasonable to conclude that learning this method of pedaling would increase efficiency. The average competitive cyclist pedals at an efficiency of about 20% but the range is substantial, ranging from about 16% to 25%. If we can both increase Vo2 max and improve efficiency, the improvement gains are multiplied, not added. So, if we start with an already elite athlete who has a VO2 max of 70 and an efficiency of 20% and can increase him to a VO2 max of 82 (the improvement see by Dixon and not unheard of) while increasing his efficiency to 24% we should see a total power improvement of 40%. Is this possible? We will have to wait to find out. Certainly those starting at lower VO2 max levels and lower efficiency numbers have more room for improvement than those with already high numbers one would expect.
But, wait, there is more!
There is something else very valuable to be learned from these power meters. Because they are mounted on the actual bike of the user they can be used to assess whether the rider's technique changes during a race or hard training ride, as the rider tires. Let's assume you have your rider pedaling in an optimum technique when you test him. The question is what does he do during a race. With these second generation meters it would be easy to compare the pedaling form at the beginning of a ride or race to that at the end. If there is a big deterioration in form from beginning to end it is safe to assume that endurance is an issue and more training effort should be placed to improve endurance than on trying to increase power. But, if form stays good despite the effort over time then it would reasonable to assume that endurance is good and the training emphasis can be placed on improving power. Without this information, such decisions are nothing more than guesses.
But, wait, there is more!
If one also does bike fitting one will be able to tell how changes in bike fit really affect power production technique. No more guessing. Further, if a rider continues to have trouble bringing up on the backstroke this could be an indication that pedal speed is too high or crank length is too long. This new type of power meter should prove to be a very valuable tool to make sure cyclists are properly fit to their machines.
Increasing power requires increasing the average power around the pedal circle. There are only three ways to increase the average power around the circle. 1) increase the peak power (push harder or make the pedals go faster), 2) reduce the negatives or, 3) broaden the force application (pushing on the pedals for more of the pedal circle). Whatever method is used the result is the rider must increase the average power put out in one pedal revolution. If one wants to double the power without changing technique one must either push twice as hard or make the pedals go twice as fast while pushing just as hard. Or, one can improve pedaling technique by broadening the portion of the pedal circle one produces significant power. iCranks will make it possible to know which is the most effective method to use for any given rider and to measure the effectiveness of the training plan.
iCranks are currently scheduled to be available soon (delay is awaiting regulatory certification of the radios I am told) and are now currently available for pre-order. Pre-order and save 15% on the price when ready to ship (cost expected to be around US $3,200 - includes dual mode PowerCranks). Take me to the order page, I am ready!