Thanks for any thoughts.
contraception
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I thought that’s what the personality was for…
My thinking is that the steeper you ride, the more you are able to stay aero while keeping the hip angle from closing too much, thus riding aero while limiting power loss. But I don’t really know what I’m talking about.
The steep position is to allow you to maintain power while going aero.
Ideally your body would be in exactly the same position as on a road bike, just rotated until your back is parallel to the ground.
As I understand it, though I could be wrong, it evolved out of an aero reasoning. By taking an upward (and strong) position (think of climbing on a road bike) position and rotating it forward around the bottom bracket you could maintain a strong position while getting more aero. Then people started feeling like they could run better from that position. Dan has some good articles on it (which I’m quoting from memory above - my apologies if I’ve gotten it wrong).
what thunderlegs said.
basically it allows you to keep the necessary hip angle while getting into a lower more aerodynamic position. It also helps to keep your upper body in a more nuetral position to take the pressure of supporting your upper body away from your muscles and distribute it to the skeletal system.
i really don’t want to be wrong on this but i’ve no time to look it up, here goes …
i think this is one of the debunked myths of the forward/steep seat angle. somebody did the math to show that going from 72* to 78* doesn’t come close to keeping the same hip angle if you are dropping from hands on hoods to elbows on aero bars. it helps get you a little lower but you still have to bend more at the hip and probably along the back. so depending on your hip flexibility and willingness to arch the thoracic spine (constricting the diaphragm) is more determinate of the ability to ‘get aero’ - throw in here, you also have to be able to look where you are going!
i feel you are trying to optimize the two. you can only bend so far at the hips because most of us have tight hamstrings (hamstrings go from the lower leg to the pelvis) but you want to bend a good bit but not too far (that’s a medical term) to get power from the big ol’ glutes (when the gluteus maximus takes its fixed point from the pelvis, it extends the femur and brings the bent thigh into a line with the body - it’s used to stomp down on the pedals). think 'half-squat.
so you bend forward until the hamstrings are at the edge, bring the seat forward to get a little bit lower, drop the seat a tad to take some stress off the hamstrings and get a little lower, put the weight on the elbows so the core doesn’t have to work to support the upper body. all to maintain power, or some are willing to sacrifice a little power, to get more areo. draw two curves, one of the power loss as you bend at the hips and and another areo drag as you come up and then optimize the two. actually, a third would be the bend of the back causing constriction of the diaphragm (assuming you have a ‘type B’ back, as i believe J Cobb immortalized it) {wish he was here to jump in}. and i’m sure there are other factors - hopefully others will join in.
what i would like to see is the power optimization for a ‘ballerina in a vacum’ take hamstrings out of the equation (the subject can put their chest on their thighs with knees straight - no problem) and there is no aero factor. keep the spine straight (with natural curves). adjust the seat and aerobars (3 points in space) and find where the best angle is. that’s the ‘base case’. then you modify from there to accommodate individual morphology.
re-reading this i realize how much this is a gross simplification but still are starting idea. you still need to look at the individuals characteristics to get a fit. spinner/masher, strong quads/weak, strong glutes/weak, long femur/short, and many more
still what wins is probably what feels comfortable to the rider.
also see this:
http://forum.slowtwitch.com/gforum.cgi?do=post_view_flat;post=1176904;page=1;sb=post_latest_reply;so=ASC;mh=25;
‘While a lot of roadies might poo-poo triathletes’ strange forward position, Kautz clearly demonstrated how it had evolved as means of limiting stress on hamstrings. The position puts less stress on the hamstrings, but also has to accommodate a hip angle that’s still tight enough for the gluteus muscles to fire. A basketball player, for example, has to compress his hip angle in order to explode up from the ground when jumping to dunk the ball.
Kautz, however, showed that rather than continually moving a triathlete up and forward to remove stress from tight hamstrings, the rider could be better off - and faster - by simply lowering the saddle. If the hamstrings are tight and the seat is high, the athlete may tilt the pelvis back to reduce the pull on the hamstrings. That in turn collapses the diaphragm and robs perfectly good breathing area, puts strain on the lower back and prevents the quads from getting up over the pedal and pushing harder. Lowering the saddle so that the knee bend at bottom dead center is 30-35 degrees rather than 25-30 degrees could reduce the pull on the hamstrings enough that none of that rotation occurs.’