iCranks, the first true second generation power meter, is coming soon
What is a 2nd generation power meter and what are iCranks? A first generation cycling power meter is what we are all used to - a device that attaches to the bicycle that gives the rider their actual power while they are riding and it collects that power (and some other metrics like HR and speed) for later analysis. A true second generation power meter does all this but also is able to give and collect individual pedal force information to allow the rider to analyze pedaling technique and muscle use. This can only be done when there are two power meters located in each crank, pedal, cleat, or shoe and when there is appropriate software to analyze the data. The iCranks power meter is located in the crank arm of the basic PowerCranks and will come with software that does this analysis. This gives the iCranks the ability to measure and display the riders pedaling technique and to measure actual muscle weaknesses in real time (indoors in front of the computer) or using saved data for later analysis. From the iCranks web site here are two examples. One rider, labeled "bad technique" has substantial issues that, I think, are pretty obvious.
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. Since the total power is the average power for the entire stroke circle, the ideal pedal stroke should be the variation in this force application pattern that results in the highest average power around the circle. 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 what a rider with lots of issues looks like on the riding on the iCranks (locked into regular crank mode) TA recording of a ride looks like.
And, here is an example of data from a rider the iCranks calls having good technique. While much better technique there is still room for improvement.
Now that you have seen what the data looks like here is how one might analyze that data. Let's start with the "bad technique" rider using a "typical" screen shot.
Before I move on I want to discuss the term pedaling in circles. We can see from this shot that the pedaling torque graph looks pretty circular but isn't centered and is not quite a perfect circle. Most people think "pedaling in circles" means equal pressure around the entire circle as shown by the blue tracing below. But, this would only be the case if we weren't pedaling in a gravitational field.
If we are in a gravitational field the absolute circular pedaling force diagram is moved to the right, increasing the down forces and decreasing the up forces that would be on the pedals if we were pedaling in space. When we move the circle over we can see that this rider is very close to this optimum except for the top half of the circle.
Let's get back to looking at both legs. What can we learn from this data?
It is easy to see a couple of things right off the bat? We can see that the left leg is substantially better than the right leg, having both a higher peak down force and less negative force on the backstroke such that it is averaging 81 watts around the circle while the right is only averaging 57 watts, a 24 watt (30%) difference between the legs. Add them together and we find the rider is generating 138 watts, the number he would see on his power meter (be it first or second generation). But, here, the imbalance information is real, rather than calculated as done by all 1st generation power meters (a 1st generation PM would calculate a left leg power of about 73 watts and a right leg power of 66 watts, an imbalance of only about 10%, substantially underestimating the imbalance and one wouldn't know there is a huge issue on the back stroke. Imbalance information is important to know as athletes with substantial leg imbalances are more prone to future injury. And, knowing exactly where the imbalances are helps in working to correct them. 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 if this rider could simply eliminate the negatives would give him an extra 18 watts here. That is a 13% power increase from just eliminating the negatives on the upstroke.
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. Afterall, the above example got the imbalance and was just off on the magnitude. The answer is sometimes combined torque power meters get it completely wrong and backwards. Let's look at why this is. Computrainer or SRM, because there is only a single power pickup point, are forced to make the assumption that all power generation comes on the downstroke and nothing (positive or negatvie)is done on the upstroke. 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. So, the above data on a first generation power meter would know the left leg is actually pushing 81+5 watts for a total of 86 watts and the right leg is actually pushing 58 + 13 watts for a total of 71 pushing watts. When we subtract the other sides upstroke negatives for each side the left side would look like it doing 86-13 watts, or 73 watts and the right side would look like it was doing 71-5 watts, for a total of 66 watts, substantially different than what is actually going on. Only when the back stroke portions are equal will this analysis reflect reality regarding balance. Here is another real world example of how wrong this can be, a rider whose right leg pushes harder than the left.
But, in this instance, we find the right leg pushing harder (821 vs 740 watts, peak 646 vs 633, avg), 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. But, how does he do this. Knowing he has to do it and doing it are two different things. That is why iCranks come with PowerCranks because that is what PowerCranks do. The independent nature of the cranks force the rider to unweight on the back stroke.
But, it is also clear that there is a substantial weakness across the top. If this rider could get the top to be as "circular" as the bottom there is room for plenty of power improvement. How to do it? Well, PowerCranks help with this also. Notice that the power changes around the circle are smooth. Eliminating the negatives on the backstroke will naturally increase the force across the top also, but perhaps not as much as we would like. The graph below illustrates the actual form changes measured in one rider after 3 months training with PowerCranks compared to the circular "ideal" (the orange curve).
Notice the rider has eliminated the negatives but only seen a small improvement across the top, still being substantially under the circular ideal. This pattern change would result in a 35% power increase if the max pushing force were kept the same.
Can more be done. Again, with PowerCranks the answer is yes and quite easily. It is simply a matter of getting serious about training this aspect of the stroke and not being afraid to look a little silly to your friends. With PowerCranks it is possible to apply the training principle of "overload" training, add resistance to the top part of the stroke so the rider gets used to putting more pressure on the pedal than normal. Do this enough and when the resistance is removed (for a race) the muscle memory remains and this area of the stroke is improved. But, how to do this? 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 this wouldn't work because the additive force at the bottom 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. 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?
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.
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 in a rider at this level 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 and using the best crank length for them (PowerCranks include the capability to easily change crank length). See our discussion regarding crank length.
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. A circular pedaling pattern is the pattern that maximizes the average power compared to the maximum around the circle. 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 $3,500 - includes dual mode PowerCranks). Take me to the order page, I am ready!