The fusion of biomechanics and aerodynamics
We’ve recently been to the velodrome in Büttgen again to conduct another aero project with our colleagues of STAPS. The fast legs that were to be tested and optimized belonged in this case to pro triathlete Daniela Sämmler who made the whole test very pleasant due to her extremely friendly manners. Her coach Utz Brenner was involved in the test protocol, too, just like Stefan Keul, bike expert of Daniela’s bike sponsor Canyon.
In this blog I would like to share some impressions of what the procedure of such an aero fitting by STAPS and gebioMized is:
At the beginning, Daniela’s very own athletics are being checked. In various tests we are looking for small weaknesses with regard to mobility, flexibility and stability. The focus is above all on the optimization potential for the aerodynamic bike position, run- and swim-specific causes are being considered as well, however (e.g. in case one-sided breathing during the swim leads to asymmetries in the back- and shoulder area). Daniela only shows minor weaknesses (e.g. strengthening of Gluteus medius) that can from now on be considered in her regular athletics training.
The second step consists in looking at Daniela’s position on the stationary trainer. This “baseline measurement” serves to analyze all contact points via pressure mapping technology as well as joint angles and movement quality in various crank positions via video analysis. Also here we are working on the same questions: where are optimization potentials recognizable, how stable is the position already, how well do athlete and contact points harmonize already? In Daniela’s case we can take some notes at this point:
- Saddle position and saddle model lead to increased pressure in the symphysis area (picture 1), which indicates an unstable pelvis position and an increased number of “saddle shifts”.
- Foot position is very pointed, the knee angle thereby is opened so wide that the seat height must be questioned as well (picture 2).
- The position is so compact that the pedaling movement goes backward-down. This could demand more energy than necessary.
- Although the hip angle is already small in the top crank position, Daniela’s very good mobility fans hopes for even more potential.
All assumptions are written down and nothing is changed yet as we objectively do not yet know how aerodynamic the position really is. Therefore, we now go to the track in order to measure the CdA as well as the stability of her position in real time. To do so we use the Track Aero System (Alphamantis, CA) as well as a new software development by gebioMized for measuring saddle pressure. Both systems send their data in real time via WIFI so that the results can already be analyzed during the run in order to discuss possible potential in our expert panel immediately.
In order to determine the drag that is also called CdA in the field of aerodynamics, we use measurement technology on the bike that is Formula 1 worthy: With a small sensor we are collecting all ANT+ signals that are sent by Daniela’s Canyon during the test run: performance data, cadences, speeds etc. But not only Daniela and her bike need to be taken into account in order to neatly determine the drag; also environmental conditions like temperature, air moisture and all characteristics of the wooden track (length, curve inclination etc.) are considered. As soon as our measurement technology is ready for use, Daniela starts racking up miles while we conduct a first baseline measurement and determine her aerodynamic input value by means of the Alphamantis system.
The analysis of the pelvis stability on the track clearly shows some optimization potential: Each outlier in the progressive graph stands for a “shift”, i.e. for an “active movement of the pelvis” to the back. These movements cause turbulences in the area of back and shoulders and therefore are detrimental to aerodynamics. At the same time the power transfer in the direction of the pedal is negatively influenced by each shift. In Daniela’s case we measure 7.5 shifts per minute that is equivalent to a time interval of 8 seconds between shifts. The standard deviation of the ‘Center of Pressure’ shows with 18.5 a conspicuous value of instability as well.
Actions and re-tests:
After a thorough analysis of the baselines we are drawing up a plan in what steps we will take actions on the position in order to (hopefully) reach some optimizations. This run list is very individual for each athlete. Each action is checked in a re-test whether it really leads to an improvement. In Daniela’s case, our “master plan” looks as follows:
- Change of saddle model (from SQLab 613 Tri to COBB JOF 55)
- Reduction of seat height
- Adjustment of saddle position to the rear with the objective of optimizing the pedaling movement (without affecting the position of the pelvis on the saddle)
- Bending of the extensions
- Test of two extension positions
- Test with lowered front end
At this point we shorten the report and directly present to you the comparison of the initial position to the final position. We achieved the following objective changes:
Biomechanics & stability
- The pelvis “stands” on the same saddle area as before, but significantly more stable. The number of shifts was reduced from 18 to 0
- The standard deviation of the ‘Center of Pressure’ on the saddle was reduced from 18.5 to 3.7 (!)
- The knee has shifted further backwards so that the pressure phase can be conducted more effectively downwards
- The foot position is flatter by 11° degrees in the lowest crank position so that the pressure phase can be conducted longer
- the improved stability on the saddle has already led to positive tendencies by only changing the saddle (savings: approx. 1-2 watts @40 km/h)
- Daniela’s position was “equalized” in order to make her sit less compressed. This way her back became flatter and the head was lowered (savings: approx. 2-3 watts @40 km/h)
- the “game changer” was the installation of a 7° incline spacer. Due to the improved stability in the upper body and the greater “length” of arm- and shoulder areas Daniela could lower her head significantly and reduce her shoulder width noticeably (savings: approx. 6-8 watts @40 km/h)
- in the equipment analysis we tested potential other helmet manufacturers in order to find out whether there is some aerodynamic potential in the helmet choice as well. We could not find a “faster” helmet for Daniela
The session with Daniela shows that biomechanics and aerodynamics should go hand in glove if an athlete wants to reach the optimum for his/her position on the bike. With regard to the Ironman distance, we could save Daniela all in all approx. 12 watts at 40 km/h. To her circumstances we are therefore talking about an improvement above 5 % that will save her on 180 km – in theory – around 5 minutes riding time. Without a considerable gain in stability aero improvements would not have been as significant as they were, without adjustments of the cockpit we would not have reached a significant CdA reduction neither. The parameter “stability” serves us as important control parameter to detect whether there still is potential or we are exaggerating it aerodynamics-wise. In addition to this, increased stability increases the chances that the position can be held over a longer period of time, e.g. 180 km. We always try to attain “passive improvements”, i.e. find a faster position that does not demand more active use of physical strength than necessary. You still can take active measures (“shrug”) afterwards, especially if you are a time trialist.
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