A little more science about seat tube angles

Triathlon Forum
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With the recent discussions of seat tube angles and the science (or lack of) behind it, I felt compelled to offer some info on a study we recently completed. As with most research it probably raises more questions than it answers (sorry). I cannot report the specific data since we will be submitting it for publication, but I can give an overview of the study and the results.

Research Question: How does seat tube angle (73 vs 81) influence oxygen consumption, HR and pedaling cadence during a simulated time-trial and subsequent run performed at identical workloads?

Subjects: 10 experienced, competitive age-group triathletes.

Methods:

*Initial Visit *: Each subject performed a 40-minute “time-trial” on a Serrota size cycle mounted to a Compu-trainer at a seat-tube angle (STA) of 76 degrees (center of the saddle was mounted directly over the seat-tube). 76 degrees was used because it was between the two STA’s we were investigating 73 vs 81 (same as Garside and Doran study). Seat height, top tube length and aerobar position were set to achieve the following body angles with pedal at bottom of pedal stroke (crank arm parallel to seat tube): 90 degrees hip flexion, 25-30 degrees of knee flexion, 90 degrees of shoulder flexion and elbow flexion (positioned in aerobars). Following a 5-minute warm-up subjects were asked to ride at a self-perceived “race pace” and could adjust workload as needed. Average wattage during the last 5-minutes was recorded and was used to set the workload for the subsequent trials. Subjects immediately (less than 1 minute) transitioned to a treadmill and ran at self-perceived race effort for 10 minutes, running pace was recorded and used for the following trials.

Visits 2: Subjects returned to perform another 40-minute time-trial at either a 73 or 81 degree STA. STA was counter balanced so that half the subjects rode at 73 first and half at 81 first. Seat height, top tube length and aerobar position were adjusted to maintain consistent body angles as described in the initial visit. During a 5-minute warm-up wattage was ramped up to the predetermined workload (from the initial visit). Wattage was held steady for 40-minutes, however cadence was allowed to vary. Subjects remained in the aerobars the entire time. Expired gases were collected using a portable metabolic analyzer as well as heart rate. Subjects then transitioned (less than 1 min.) to the treadmill while still wearing the portable metabolic analyzer and performed a 10 minute run at the pre-determined pace(from the initial visit). Oxygen consumption (ml per kg • min) and heart rate were recorded and averaged for the last 5 minutes of the time-trial and the first 5 minutes of the run. Pedaling cadence was also averaged during the last 5-minutes of the bike.

Visit 3: Subject returned to perform the same procedure described above at the alternate STA to the one they rode at during their second visit.

Results: There was no differences (in fact they were nearly identical) between oxygen consumption during the cycling and subsequent run at either of the STA’s. Heart rate was higher during cycling at the 81 degree STA vs the 73 STA (although there was a statistical difference, the difference was probably too small to have any real performance effects). There was no difference in HR during the run following cycling at the two STA’s. There was no difference in pedaling cadence between the 73 and 81 degree STA.

Limitations of the study: Small number of subjects. Cycling and running times did not approximate normal triathlon times (although the run was very short, if you were going to pick up a difference in oxygen consumption or HR you would expect it to be most evident during the first part of the run, this was demonstrated by Garside and Doran). Did not collect kinetic and kinematic data that might shed light onto important biomechanical and neuromuscular factors in addition to the physiologic data. Aerodynamics were not measured with the changes in STA.

Strengths of Study: First study (that I know of) to maintain consistent body/position and joint angles at the different STA’s. Maintained consistent “race-like” workloads throughout time-trial and run, the only variable that changed was STA.

Thoughts: Although our research showed little or no difference in performance between the two STA’s, given the current body of scientific evidence (flawed and sparse as it is) it seems that riding at a steeper STA is at least equal or better than a shallower STA and should be a goal of most triathletes who ride on relatively flat courses. Especially when you consider the potential aerodynamic benefits (i.e. getting lower in the front end while maintaining the same body angles). Obviously other factors need to be considered such as inability to achieve the position due to back pain etc. or a significant drop in power (however, most people can accommodate over time), this is why a good bike fitter is essential.

Although this is my first post, it was reading many of your posts that influenced my motivation for doing this study. Thanks for the inspiration.

Special thanks also goes to Bob Duncan and the staff at Wheelie Fun Multi-sport (wheeliefun.com) in Lebanon OH, for their expertise on bike fit and use of their equipment.

Hope someone finds this information useful.

Kurt Jackson

Andrews University

Dayton, OH

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One major question: wouldn’t it be vastly better to do a study like this on non-cyclists? or perhaps even non athletes? Specificity would seem to indicate that using trained triathletes may highly favor the seat tube / torso / hip angles that the athletes are currently using. Their past training would make them most efficient on the angle(s) they are presently adapted to.

Thoughts?

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Good question, I see where you are going regarding specificity of trianing and long term adaptations. While we did not specifically control for it in our study, our subjects were using a wide range of seat tube angles on their training and racing bikes. So not all of subjects were say adapted to a steep or shallow seat-tube angle. As far as using non-athletes, it is a little difficult from a practical consideration of finding willing subjects, and novice athletes or non-cyclist are prone to giving inconsistent performance (such as bonking half-way through the trial).

Thanks for the input.

Kurt

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I think using triathletes is as good a way to test as any. After all, if there were a benefit to trained triathletes from a steeper setup, it might only be beneficial after a term of adaptation. IOW, non-trained, non-triathletes might not show benefits due to other factors, such as lack of core stability, discomfort with the head position, discomfort with the seat position, discomfort in the rhomboids and/or neck, etc., ad nauseum.

I’m glad you mentioned the aerodynamic differences of the steeper setup. Speed is what you really want to measure, not watts, but watts are the thing that is measured in a lab. Steep isn’t necessarily always more “aero”, but my gut feeling is that is usually is for most of us.

Thanks for sharing your study with us! Always good to have more information!

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One way that I found that worked for ME was the spin scan, my bike fitter hooked it up and we played with the different seat angles and positions and we fine tuned it to the one that allowed me the most efficient SPIN, and Im much faster because of it, and it was a forward position on the bike that did it.

just my 2 cents worth

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If the positioning of the subjects on the bikes was set so that in effect it did not alter in any way then what did you expect to find with a ‘percieved race pace’?

The whole difference in various positions is the total difference in position, hip torso angles etc. If you took a pro cyclist from his roadie position and increased the effective seattube angle but maintained the basic angles of his body I would take is as a ‘given’ that his oxygen consumption, HR and most probably power output would stay the same.

There was no difference in pedaling cadence between the 73 and 81 degree STA. Pedaling cadence can take years to be ‘in grained’ into a person, each person over time generally adapts to a cadence that they either feel is best suited to them, or they have found through trials is best suited for the type and style of cycling they do. I cannot see how changing angles for a short term test would effect this in any way.

I imagine a far more definintive test couldbe to take 10 triathlete, 5 who ride ‘steep’ and 5 who ride ‘shallow’ and alter alter their positions the oppsosite, including hip angles etc. Allow the subjects a longer period, say 6 months, to adapt. Then test the athletes for HR, power, VO2 etc etc and also test the athletes position in a wind tunnel and factor the whole sum into a single result set.

This would give you a better answer as it would show what the ‘costs’ of are in terms of power Vs percieved aerodynamic improvements. To me until such tests are conducted it is all just hypothises.

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If the positioning of the subjects on the bikes was set so that in effect it did not alter in any way then what did you expect to find with a ‘percieved race pace’?

The whole difference in various positions is the total difference in position, hip torso angles etc. If you took a pro cyclist from his roadie position and increased the effective seattube angle but maintained the basic angles of his body I would take is as a ‘given’ that his oxygen consumption, HR and most probably power output would stay the same.

Great point, this one of the things we were trying to find out in our study. When we were designing the study our original hypothesis was that if we kept body and joint positions the same we would probably see very little difference in any of the variables we were looking at. I suspect that most previous studies did not adequately control for body position and therefore ended up with a much too narrow hip and torso angle in the shallow position which would restrict breathing and ruin optimal muscle length-tension relationships which would artificially skew the results in favor of the steeper seat tube angle. Our study simply showed that it did not seem to make much of a difference in the short-term. But if a steeper seat-tube angle allows you to get more aero (and I know that is not always the case) than it might be worth pursuing. And, yes doing long-term studies and allowing for adaption over time etc. including wind-tunnel data would be ideal but not always practical. Thanks for your observations.

Kurt

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coupla things:

  1. thanks for doing this

  2. when you keep a 90 degree hip angle, that’s good, preserving the hip angle is an important issue none of the previous studies spoke about. but, how did you determine this? using what points on the body?

  3. if you do this again, it would be great if you also noticed the cadence rate. only one of the studies, quite an old one, mentioned this, and only as an aside. they didn’t measure, but mentioned that cadence increased at steeper seat angles.

  4. one of the studies i’d like to see done requires almost no equipment. it is just an analysis of freely chosen cadence (FCC). what is the FCC at various seat angles? ample studies demonstrate this to be in the neighborhood of 90rpm, altho this degrades in the latter stages of a longer test. altho this is a simple study, i’ve never seen anyone publish anything on it.

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It would be interesting to ask the athletes to maintain a percieved effort level whilst increasing the loading/effort required whilst maintaining position. Record this with cadence and I would bet my left one as more power is required cadence will drop, power will go down the proverbial bowl.

Factors to record:
O2 consuption
HR
Power output - every 5 mins (compare effort to actual output as angles change)
Cadence
Comfort level as percieved by the athlete

I think believing in ‘steep’ angles, above 76 degrees, is like religion, there is likely to never be any conclusive evidence in its favour that can not be shot down by some form of research. However people with faith will be able to find fault or consequence for their beliefs from the flaws found in any research findings.

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“I think believing in ‘steep’ angles, above 76 degrees, is like religion, there is likely to never be any conclusive evidence in its favour that can not be shot down by some form of research. However people with faith will be able to find fault or consequence for their beliefs from the flaws found in any research findings.”

well, okay, but in fact what actually HAS happened is that most top pro athletes, both road and tri, ride tri bars with steeper seat angles, and then steepen them up more by riding a steeper apparent angle than that angle allowable on their bikes.

and, every bit of science to date has demonstrated, without exception, that steeper is better when riding with aero bars.

but, you know how it is. shallower angles are like religion, and people of such faith will be able to find fault in any research findings.

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“… maintain a percieved effort level whilst increasing the effort required …”

and

“… as more power is required … , power will go down the proverbial bowl.”

These statements seem contradictory to me.

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There was no differences (in fact they were nearly identical) between oxygen consumption during the cycling and subsequent run at either of the STA’s.

I woulda bet any amount of money that’s exactly what you would have found. It’s the joint angles that determine performance, not seat tube angle. You held joint angles constant, and found that people perform the same at the same joint angles. All you did by changing the seat tube angle is to vary the orientation to gravity. The same work has been done by other researchers by looking at muscle activation at various orientations to gravity. It’s easy to make the bike changes – all you need to do (and all you “effectively” did) was rotate the bike around the bb axle, leaving the rider’s position unchanged.

I still think it’s a worthwhile result – people need to understand that it is how the body is positioned that matters, not the orientation to gravity. There is no inherent power advantage to any seat tube angle. Running well off the bike has nothing to do with seat tube angle, but it has a lot to do with how tight the thigh-torso angle is.

A point I would emphasize is that there is no power lost by coming forward and down. Given that is the case, I wonder why so many TT’rs and triathletes ride on slack bikes with their torsos sticking up into the wind. 81 degrees: Same power; same run off the bike; less wind resistance. Hmmm…sounds like a winner to me.

People get all hung up on seat tube angle, and that’s not it. At a given set of joint angles, the seat tube angle merely determines how low your shoulders are (ie, how “aero” you are). My bike is at 81+ degrees, and my joint angles are the same as on my road bike holding the brake hoods, sitting up into the wind. Not surprisingly, I lose no power on the tri bike (climbing included), but I’m a lot faster.

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but, you know how it is. shallower angles are like religion, and people of such faith will be able to find fault in any research findings.

I know of one elite non-drafting triathlete who, when asked why he rides with his saddle set so far back, replied, “My buddies and I just like the fact that we’re UCI compliant.” This despite that fact that UCI rules have no bearing on non-drafting long-course triathlon.

I gotta admit – that’s about the dumbest reason to choose a bike setup parameter as I have ever heard. It makes as much sense as doing an cold open-water swim with no wetsuit because, “I like to know that I’m compliant with international pool swimming rules.”

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My biggest complaint about being really steep is neck pain.

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Does that guy actually make a living at the sport?

I am a lot faster on my tri bike. By a lot I mean maybe 8% faster.

I do think this advantage falls off on long rides though, since I can’t stay aero indefinitely. Still, I am many miles down the road before I have to start sitting up. I guess I have to work on comfort and strength issues that limit my ability to stay aero.

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percieved level is not actual level, increase the actual level of the load applied to the crank/wheel.

I would guess that as more power is actually required and if the rider maintanes a percieved effort then the drop in output and at what point, from the rider will be greater on a steeper angle.

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"percieved level is not actual level, increase the actual level of the load applied to the crank/wheel. "

No perceived level is not power, but the two are intimately connected. How do you propose increasing the load on the wheel, i.e., the power supplied by the rider, without increasing the perceived exertion of the rider?

Similarly, “I would guess that as more power is actually required and if the rider maintanes a percieved effort then the drop in output and at what point, from the rider will be greater on a steeper angle.”

I don’t understand this at all. If more power is required of the rider, perceived exertion will also increase. What output are you talking about? If it’s the power output of the rider than it can’t both increase (start of sentence) and drop off (middle of sentence); to me, output and rider power are the same thing. This sentence makes it sound like you want to increase, keep steady, and decrease rider power.

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you are correct but are missing what I was hoping to see as a conclusion.

Ok if a rider on a 78 degree ST angle, based on position not seattube, and you ask them to ride at a percieved effort level with a load on the crank of A1 and you then increased the load to A2, maybe a 5% increase, how much effect does this have, remember they are percieving the effort, I would prefer a fixed level based on some test parameter obtained for each athlete. Then increase it to A3 and so on…

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Does that guy actually make a living at the sport?

I am a lot faster on my tri bike. By a lot I mean maybe 8% faster.

I do think this advantage falls off on long rides though, since I can’t stay aero indefinitely. Still, I am many miles down the road before I have to start sitting up. I guess I have to work on comfort and strength issues that limit my ability to stay aero.

Actually, he does make a living at the sport. He’s very fast. I just think he would be faster if he got his shoulders a few inches lower. That would require the saddle to come forward a couple inches.

As you and somebody else noted, a downside to riding forward and low is neck and shoulder comfort. Hits me too, around 4 hours into a ride. I need to get that limit pushed out beyond 6 hours before IM CDA. I find that moderately rolling courses help since I can sit up or stand on the climbs and keep the shoulders and neck from getting so worn out.

But hell. If the sport was about comfort we’d all stay home and sit on the couch.

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For me, the discomfort is in the crotch and lower back. I am not really sure what to do about it. I can’t lie in bed in the same position for six hours either.

I really would never want to do IM Florida. Six plus hours of no excuse to get up out of the saddle. Ouch.