04 March 2011

power, CompuTrainers and the ergo vs. the TT

I have been working out at Seattle Multisport for a few months now and lately I was feeling like I was doing it all wrong.

Some history – the last two winters I spent a lot of time at Cycle University participating in their indoor TT series. This is a 10 km or 10 mile CompuTrainer TT so you get to ride your own bike and the resistance is calculated based on your weight. The also arbitrarily add 20 lb. for your bike. Being a TT the resistance is directly related to how hard you pedal and what gear you are in, just like out on the road.

The Seattle Multisport workouts have been 'ergometer' workouts rather than a time trial. This means you enter a threshold wattage (which is based on your performance in a TT) and then ride the intervals at a percentage of this threshold. In this type of workout or 'mode' the CompuTrainer software keeps the resistance pretty much exactly the same no matter what gear you are in.
At the beginning of our ergometer workouts a few months ago we quickly realized that 1) it was hard to maintain a cadence and 2) if your speed dropped off the resistance stayed the same. This led us to believe that higher cadence was better meaning a more beneficial workout. We also realized that speed meant nothing since it was only dependent on the gear you were in and 100 rpm in your 53x21 felt the same as 100 rpm in your 53x13. So over the next few weeks we all tried to pedal faster and hold that high cadence longer.

For sure it was a good workout – especially for me who is somewhat cadence-challenged and I slowly got better at maintaining first 90 and eventually 100+ rpm for the duration of the workout. No small feat perhaps.
Then a few days ago a friend of mine (Ryan D) who apparently is much more observant than  am, started to look at the numbers of some other people we were riding these CompuTrainers with. He noticed that guys who were much lighter (the implication here is weaker, but not in a derogatory sense) and who he could beat out on the road were posting significantly higher watts/kg numbers than he was. He looked closely and these people were pedaling a LOT slower. When I read Ryan's revelation it dawned on me that I was not getting the same workout as the last two years at Cycle U. This led to some email exchanges with Tim B about whether or not I was getting in a good workout, had wasted months of trainer time and the benefits drawbacks of high vs. lower cadence workouts. Here is what he had to say.

"The way the CompuTrainer works is to put the load (the watts specified by the program) onto the wheel electronically vs. a 'resistance force' being on the wheel (a magnetic or fluid trainer) and then measuring the work that it takes to overcome the load (what an SRM or PowerTap would read in watt/seconds).  Since the load is static it is independent on gear and cadence BUT what you FEEL is going to be completely different when you pedal at 60-70 rpm vs. 100-110 rpm because the total work per second is divided by the cadence. The faster the cadence the less work there is PER PEDAL stroke even though the total work is the same per second or minute or hour. So the faster you pedal the less you FEEL the resistance on the pedal, all a matter of perception. If you want a more ROAD feel vs. a SPINNING feel then slow down the cadence and you will feel the load and the fatigue will set in. But if you spin at higher cadence your muscles over come the fatigue by shifting the work to more endurance fibers vs. strictly the fast twitch fibers. That is why we do these workouts, to teach the body to spin a higher gear when the load increases, i.e. a hill. Increased neuromuscular activation of muscle fibers is best done inside on the trainer as it is harder to do outside with wind resistance (which is why motorpacing works so well)."

"The reason to keep  the speed at the 25 mph range is so that you keep the cadence in the range that you would use outside, i.e. 90-100 rpm. If you spin at 110-120 rpm then you get the flywheel effect like a spin bike and that does not "feel" like a road ride and likely not as beneficial when transferring motor learning to what you would do outside say when you try to push a 52x16 up Juanita Hill (you wouldn't be able to maintain 110 rpm or 23 mph for long but you might push 20 mph for quite a ways)."

On reading this Ryan also helped explain things to me.

"I will try to elaborate on what I posted to my blog last night. I tried not to "get ahead of the work" of the interval by spinning up with 5, 4, 3, 2 seconds to go like I have in the past, then trying to absorb the increased resistance and then getting back up to speed and holding it through. As you saw two weeks ago this lead to high 35+ mph and on the last few, low 40+ mph. You'll recall my surprise when reviewing my PowerTap file later that I couldn't believe I had done LESS total work than the week before. I covered more miles, and at a higher average speed than ever. Record RPMs too at over 100 rpm average. But net net, less total work and I didn't feel fatigued as much.

Last night, I approached it a bit differently and thought about keeping my rest level power up a bit higher, about 230 watts average, and then when the interval started, hear me out now, I thought about just "bearing down", like they tell birthing mothers, and being one with the increased pressure, not trying to cheat it or outspin it, but just to push through it. I watched wattage on the screen and just tried to keep it at least at 350-360. I did set the threshold wattage at the start at 360 watts which is pretty huge.

These efforts turned out to be VERY fatiguing, particularly after the first half. I thought I was doing great until I looked over at Owen's and saw his watts/Kg were tracking OVER mine. I said fuck that and tried to match him on effort #6 or 7, and I did get speed, and watts/Kg up, but it turned out to take a lot out of me, and my subsequent intervals suffered and my speed dropped pretty significantly and I did cramp a bit in the end. I do not understand why I had faster speed average than Steve but whatever.

This workout last night was a new record for indoor session total Kj of work at 970. That's nearly 120 Kj more than the same workout one week prior. The RPMs were some 10 RPM less than the week prior as well."

What does al this mean?

That it takes half a brain to train intelligently. Sometimes I feel like I only have one quarter of a brain.
It also means I did not waste my time but that what I did this winter is quite different than what I did the last two years.




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