I hope this thread goes 20 pages, because it's a topic worth examining and reexamining. On this point:
Originally Posted by
Brian Ratliff
Everyone has probably seen this chart before:
[snipped]
One last observation came on a spin bike when I was cooling down from a gym session last night: There tends to be a certain RPM band around 120rpm where people tend to become very rough. Below that, it is smooth, above that, it is smooth, but there is a transition. What is actually transitioning? I now think it is transitioning between a quad dominated motion below the RPM band and a hamstring dominated motion above the RPM band, and the transition region is when the body gets a bit confused about what muscles should do what. When I focused on a rigid back and a hamstring dominated motion, the transition region seemed to disappear.
I have observed a similar "RPM band effect" riding on the LeMond Revmaster Pro spin bikes at my gym, and I agree with your analysis.
Also, the neuromuscular leap from the 175mm cranks on my road bike to the 170mm arms on the LeMond seems bigger than 10mm in diameter. The spin bike's shorter arms screw up my timing when firing the hip flexors through the top of the stroke and gauging the glute-quad overlap at the maximum moment of the power stroke (3 o'clock). I too use the spin bikes for post-lifting session recovery, so I spend most of my time in that 100-120 RPM band in lowish gearing. The flywheel also "deprives" me of the reference point that the usual dead spot in the pedal stroke would otherwise provide, so it takes me about 15 minutes to recalibrate my pedaling motion and settle in every time I climb on.
My situation is somewhat exacerbated by my size (6'3", long femurs and lower legs), which puts me at the outer limits of the LeMond's geometry (seat post maxed out, "stem" slammed, bars fully extended). Ideally, the bars would extend slightly further out, then the seat post would go a bit higher so I could rotate my pelvis further forward and flatten my back. Bike fits are always compromises, and this one leaves me a bit more upright than I would like. Is it ridiculous that I care about getting long and low on a bike that isn't going anywhere? Yeah, a little bit but it's a comfort issue, too, as I occasionally drope in on a real spin class and have to hammer in this Frankenstein position.
Anyway, all of that leaves my hip angle slightly closed off at the top of the stroke, even with the shorter cranks. My hip flexors default into taking up the additional work through the 12 o'clock position, which is not a good situation given how this coincides with the actual dead spot on a road bike crank and (as someone pointed out earlier) how small the hip flexors are compared to the big leg muscles. My workaround is accentuating the hamstring contraction in the back end of the stroke and really driving with the glutes at the top of the stroke. Bookending the problem in this way has worked out OK thus far.
Incidentally, I've wheeled the spin bike in front of a mirror and tried a variety of positions and approaches to pedaling before settling on my current setup. I have to say that my pedaling looks smooth enough, both head-on and from the side, but a flywheel will do that and it still feels weird. Less weird than it did before I started mucking about with all of this, though.
Yeah, I spend my spin class appearances wondering how nice it must be to be a normal person grinding away in sit-up-and-beg.
