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mwright2cycle
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Our local YMCA is putting on an indoor triathlon and I am trying to come up with a formula to help them determine the winner of the cycle segment.
The indoor triathlon consists of a 10 minute pool swim, a 20 minute cycle on an indoor, stationary bike, and a 20 minute run on the treadmill. The winner of the swim segment is clearly the one that swims the furthest in 10 minutes, and the winner of the run segment the one that runs the furthest on the treadmill, but on the spin bikes the distance reported at the end of the session is not the distance traveled by revolutions of the fly wheel.
The spin bikes that are being used are the Keiser M3 (http://www.keiser.com/m3/mscience.html ). They have a gear selector that allows the user to set the resistance on the bike between a setting of 1 and 24 with 1 being the easiest and 24 the hardest amount of resistance. The bike also has a computer that displays current cadence (RPM), watts, Kcals, and “distance”. At the end of the biking session, the display is summarized for average cadence, average watts, and total “distance”.
From what I understand, for every 200 revolutions of the flywheel, the Keiser M3 will display a “distance” of 1.0 (http://www.powerbiketrain.com/Keiser-M3.html ) regardless of the gear selection. If you are riding a bike on the road this is not the case—the harder the gear, the further the bike travels per revolution of the crank.
The VP of Sales & Marketing at Keiser, Darrin Pelkey, has provided this explanation of how wattage is computed on the Keiser M3:
Watts are calculated from the gear setting. A potentiometer is attached to the magnet holder (the round cone shaped disc at the end of the shifter cable). As the shifter is moved, the cable rotates the magnet holder. A potentiometer is rotated by the rotation of the magnet holder, thus feeding information to the computer on the position of the magnet holder. The rotation of the potentiometer is broken down into 24 gear settings. A dynamometer was used to test and develop a table of wattage at various gear settings and speeds. The speed of the crank is determined by a magnet attached to the large pulley on the right crank arm and a magnetic switch attached to the circuit board in the magnet holder assembly. Each time the magnet on the pulley passes by the magnetic switch, a signal is sent to the computer to compute the RPM's of the crank arm. Power equals force times velocity. The force is determined by the magnet position and the speed by the crank speed. The lookup table is programmed into the computer and the computer simply looks at the gear setting and speed and goes to the lookup table to find and display the Watts for those two settings.
One way to solve the problem would be to require the participants to keep the bikes in a fixed gear, but it is hard to pick a gear that would suite the inexperienced and experienced participant alike; a fixed gear that is easy enough for a younger participant would be a disadvantage to a strong, more experienced cyclist. Also, the gear selector is very easy to move, and it would be hard to monitor the bikes to ensure that no one cheated even if just by accident.
Based on my understanding of this problem, it is not possible from the data supplied by the Keiser M3 computer to determine the actual distance traveled. If the bike were kept in a fixed gear, then this could be determined, but if the participant is allowed to vary the gear, then the only way to determine the actual distance would be to know what gear the bike is in per revolution of the fly wheel. If it is true that actual distance cannot be determined, then it seems that the only way to rank contestants on the cycle segment is by the amount of work that they put forth during the 20 minutes.
One theory currently being proposed to determine the amount of work is to take the average watts reported at the end of the 20 minute cycle session and divide that by the rider’s weight in kilograms, giving you the power to weight ratio. I disagree with using the rider’s weight in the calculation. I know that weight matters when riding a bike outdoors because you actually have to propel the bike forward, but on a stationary, indoor bike I do not believe that weight matters, though admittedly I really do not know. My idea for determining the amount of work done is to take average watts * distance (revolutions of the fly wheel) or just the average watts itself.
Here is some test data that we put together on 3 participants riding the Keiser M3 for 20 minutes:
rider,watts,distance,fly wheel revolutions,Kcal,weight (lbs),weight (kg),watts/weight (kg),watts * distance
A,330,10.8,2160,880,147,66.67807839,4.949152825,3564
B,360,10.2,2040,1102,161,73.02837157,4.929590956,3672
C,290,9.8,1960,1163,200,90.718474,3.196702802,2842
Using watts/weight (kg), rider A wins at 4.949 watts/kg; using watts * distance, rider B wins at 3672. And since watts itself is a function of the cadence, I think you could also just use average watts so that rider B wins at 360 avg watts.
If you have time to consider this interesting problem, what is your opinion on how to determine the rankings for the cycle segment of our indoor triathlon? Is the weight of the rider a factor on a stationary, indoor bike?
Thanks!
The indoor triathlon consists of a 10 minute pool swim, a 20 minute cycle on an indoor, stationary bike, and a 20 minute run on the treadmill. The winner of the swim segment is clearly the one that swims the furthest in 10 minutes, and the winner of the run segment the one that runs the furthest on the treadmill, but on the spin bikes the distance reported at the end of the session is not the distance traveled by revolutions of the fly wheel.
The spin bikes that are being used are the Keiser M3 (http://www.keiser.com/m3/mscience.html ). They have a gear selector that allows the user to set the resistance on the bike between a setting of 1 and 24 with 1 being the easiest and 24 the hardest amount of resistance. The bike also has a computer that displays current cadence (RPM), watts, Kcals, and “distance”. At the end of the biking session, the display is summarized for average cadence, average watts, and total “distance”.
From what I understand, for every 200 revolutions of the flywheel, the Keiser M3 will display a “distance” of 1.0 (http://www.powerbiketrain.com/Keiser-M3.html ) regardless of the gear selection. If you are riding a bike on the road this is not the case—the harder the gear, the further the bike travels per revolution of the crank.
The VP of Sales & Marketing at Keiser, Darrin Pelkey, has provided this explanation of how wattage is computed on the Keiser M3:
Watts are calculated from the gear setting. A potentiometer is attached to the magnet holder (the round cone shaped disc at the end of the shifter cable). As the shifter is moved, the cable rotates the magnet holder. A potentiometer is rotated by the rotation of the magnet holder, thus feeding information to the computer on the position of the magnet holder. The rotation of the potentiometer is broken down into 24 gear settings. A dynamometer was used to test and develop a table of wattage at various gear settings and speeds. The speed of the crank is determined by a magnet attached to the large pulley on the right crank arm and a magnetic switch attached to the circuit board in the magnet holder assembly. Each time the magnet on the pulley passes by the magnetic switch, a signal is sent to the computer to compute the RPM's of the crank arm. Power equals force times velocity. The force is determined by the magnet position and the speed by the crank speed. The lookup table is programmed into the computer and the computer simply looks at the gear setting and speed and goes to the lookup table to find and display the Watts for those two settings.
One way to solve the problem would be to require the participants to keep the bikes in a fixed gear, but it is hard to pick a gear that would suite the inexperienced and experienced participant alike; a fixed gear that is easy enough for a younger participant would be a disadvantage to a strong, more experienced cyclist. Also, the gear selector is very easy to move, and it would be hard to monitor the bikes to ensure that no one cheated even if just by accident.
Based on my understanding of this problem, it is not possible from the data supplied by the Keiser M3 computer to determine the actual distance traveled. If the bike were kept in a fixed gear, then this could be determined, but if the participant is allowed to vary the gear, then the only way to determine the actual distance would be to know what gear the bike is in per revolution of the fly wheel. If it is true that actual distance cannot be determined, then it seems that the only way to rank contestants on the cycle segment is by the amount of work that they put forth during the 20 minutes.
One theory currently being proposed to determine the amount of work is to take the average watts reported at the end of the 20 minute cycle session and divide that by the rider’s weight in kilograms, giving you the power to weight ratio. I disagree with using the rider’s weight in the calculation. I know that weight matters when riding a bike outdoors because you actually have to propel the bike forward, but on a stationary, indoor bike I do not believe that weight matters, though admittedly I really do not know. My idea for determining the amount of work done is to take average watts * distance (revolutions of the fly wheel) or just the average watts itself.
Here is some test data that we put together on 3 participants riding the Keiser M3 for 20 minutes:
rider,watts,distance,fly wheel revolutions,Kcal,weight (lbs),weight (kg),watts/weight (kg),watts * distance
A,330,10.8,2160,880,147,66.67807839,4.949152825,3564
B,360,10.2,2040,1102,161,73.02837157,4.929590956,3672
C,290,9.8,1960,1163,200,90.718474,3.196702802,2842
Using watts/weight (kg), rider A wins at 4.949 watts/kg; using watts * distance, rider B wins at 3672. And since watts itself is a function of the cadence, I think you could also just use average watts so that rider B wins at 360 avg watts.
If you have time to consider this interesting problem, what is your opinion on how to determine the rankings for the cycle segment of our indoor triathlon? Is the weight of the rider a factor on a stationary, indoor bike?
Thanks!
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