Spine Concept EVO is the result of a 3-year long study on the BICYCLE-RIDER INTERFACE, whose primary objective was to gain a better understanding of the biomechanics of bicycling and the effects that saddle and position have on the biomechanics of a cyclist.
The study has utilized a fitting bike on which the positions of the saddle, handlebars and pedals can be independently manipulated. The bike has been custom instrumented with force transducers at the seat post, stem and bottom bracket. The goal was being able to measure those characteristics that so far have been determined only by feel. The anlysis of the huge amount of data that this study produced was the generator of our new saddle selection concept and of a new range of dedicated products.
The initial group of experiments was performed to understand how the forces generated when pedalling are distributed on the contact points at:
Different power outputs
Different hands position on the handlebar (Tops vs. Drops vs. Hoods)
Different handlebar Stack and Reach
The second group of experiments was performed to learn more about:
Front-Rear Wheel Rider Weight Distribution (it showed substantial differences between different types of bike fitting methods). Center of Pressure Location (it defines the correct anatomical centre of a saddle).
The final phase of the study investigated the body/machine interface more in details through: Saddle Discrimination Ability, a triangle test run to find the most reliable subjects that later performed a Subjective Rider Comfort test, which determined the relation between anatomical characteristics and shape, width of their preferred saddle.
Multiple subjects have been taken their anthropometric/anatomic measurements and rode on a stationary bike with their own bike fitting measurements (either self fitting or commercial bike fitting). The stationary bike was equipped with several strain gauges on every contact point, a power meter and a speed/cadence computer.
Data were recorded and analysed to determinate any existing correlation between subjective feelings and numerical results. Final report generated the Spine Concept EVO and a new range of products to better answer consumers’ needs.
2. Power/cadence study
In this experiment, riders were asked to maintain a cadence of 90 RPM at power outputs of 1, 2, 3 and 4 watts per kilogram body mass (W/kg) in a randomized order. In the second phase of the study, riders maintained a power output of 2 W/kg while pedaling at cadences of 60, 70, 80, 90, 100 and 110 RPM in a randomized order. In both of these studies, the force-instrumented fitting bike was adjusted to fit the individual rider.
The results from the power study indicate that apprixmately 40% of body weight is supported by the saddle and 15% at the handlebars leaving 45% at the bottom bracket. Overall, the vertical forces at all contact points must add to 100% of body weight and results have verified the total forces to be very close to this. The forces on the saddle and handlebars decrease at greater power outputs because of the greater pedal forces that are required to generate the higher power outputs. At 4 W/kg, saddle vertical forces are 13% less than at 1 W/kg; bottom bracket forces are about 13% greater and handlebar forces are modestly lower. From this study, a greater understanding of typical rider interface force patterns has been generated.
3. Handlebar stack and reach study
This experiment was conducted to study the affects of the three standard hand positions (tops, hoods, drops) have on the bike rider interface forces.
As riders shifted from the hoods to the drops the percentage of their weight supported on the handlebars increased of 5%.
As riders shifted to the tops surprisingly approximately 3% more weight was supported on the handlebars.
WEIGHT DISTRIBUTION (FRACTION OF BODY WEIGHT)
TOPS, HOODS AND DROPS
4. Front-wheel Weight Distribution
Weight distribution on the bike wheels is a critical element in bike handling and riding comfort. This experiment was set to measure the weight distribution on front and rear wheel with different types of bike-fitting. We chose common commercial bike fittings, self-fittings from expert riders and bike fittings from two Pro Tour teams. The results show that commercial bike fittings focus on percieved comfort or aerodynamic efficiency, while professional athletes and expert enthusiasts have a very similar weight distribution that improves bike handling.
|Critical P Value|
corrected to .0166
|Professional Data||Amateur Data|
|Pro Fit||Self-Fit||Bike Fit 1||Bike Fit 2|
|P-Value when compared
to professional fit
5. Center of pressure study
The center of pressure is the exact center of all the forces acting on the saddle. The study analysed what happens to the CoP when the saddle is moved along various points of the rails
Center of pressure (CoP) movement at various saddle positions
6. Saddle Discrimination Ability and Time Frame Test
The goal of this study was to select the most sensitive subjects to then perform the Subjective Comfort test. We needed to understand if individuals are able to discern differences between saddles during stationary bicycle riding and we were able to show that only a fraction of them are.
A TRIANGLE TEST determines how sensitive riders are to their saddles and if they could consistently distinguish between saddles. The test exposes the subject to three trials of two different saddles (“A” & “B”) presented in a random order, for example “A, A, B”. The subject is told that she/he is going to ride on two different saddles and that one of the saddles is going to be ridden twice for a total of three sessions. The order in which the saddles appear is random as is which saddle will be ridden twice. The subject is blinded as to which saddle they are riding as well as which saddle has been repeated. At the end of the 15 minute trial the subject tries to identify which saddle and trial was the repeated or which one was ‘odd man out’.
Why 15 minutes?
To set some of the parameters for the studies and to determine the sensitivity of the subjects to changes in the saddles a number of pilot tests were first conducted. The first pilot test determined the time frame over which a rider became accustomed to a change in bike conditions, these included saddle, positioning, cadence and power. The forces that the rider exerted onto the bike were examined over the course of one 20 minute trial. From this data, it was determined that after five minutes on the bike the forces stabilized. For this reason a five minute acclimatization period was chosen for all test conditions and for the sixth minute data was collected. The pilot data graph used to select the five minute point can be seen in Figure 2 below.
7. Subjective Comfort Test
Are there individual anatomical measures (e.g. leg length, pelvic width, spine flexibility) that can predict saddle comfort?
We identified individual anatomical variables that correlate with the perceived saddle comfort, such as pelvic rotation and spine flexibility. We couldn’t find a clear correlation between sit bones width and saddle width. Slower riders tend to choose wider saddles and vice versa.