3.1.3.4 Force Reduction
Requirement
The dynamic interaction between the athlete and the surface is significant to the performance and safety of the athlete. Therefore the ability of the surface to reduce force (absorb energy) is important. The force reduction shall be between 35% and 50%, at any surface temperature between 10°C and 40°C. If, at the time of measurement, the temperature of the surface is outside this range, it shall be permissible for the results obtained to be corrected for temperature, by interpolation from a graph of force reduction against temperature for the precise surfacing system installed, previously obtained by laboratory testing. If no graph is available then testing
outside the surface temperature range shall not be undertaken.
Because of the fact that it is required to install greater thicknesses of synthetic surface at take-off areas and at the ends of runways, it is possible that results obtained in these areas may fall outside the above range.
Method
A full description of the apparatus and details of the method are given in EN
14808:2005, except that the low-pass filter shall have a 9th order Butterworth characteristic.
The 95% confidence limits of this method are calculated at plus or minus 1%. At least one measurement shall be made for every 500m2 of normal thickness synthetic surface, with a minimum of twelve (12) measurements over the facility. The test positions shall be as follows:
1. At the discretion# of the test laboratory in any lane around the first radius*
2. In the centre of lane 2 at the 130m mark on the back straight
3. In the centre of lane 5 at the 160m mark on the back straight
4. At the position of lowest thickness on the back straight*
5. At the discretion# of the test laboratory in any lane around the final radius*
6. In the centre of lane 1 at the 320m mark on the main straight
7. In the centre of lane 4 at the 350m mark on the main straight
8. In the centre of the outer lane at the 390m mark on the main straight
9. At the position of lowest thickness on the main straight*
10. At the discretion# of the test laboratory at any position (except the high-jump
take-off point) over the semicircular area. Where there are two semicircular
areas, a test shall be performed on each of them.
11. At the discretion# of the test laboratory at any position (except the reinforced
areas) on each of the runways (Long Jump, Triple Jump, Pole Vault, Javelin
Throw) and in the steeplechase lane.
#Whenever the selection of the test location is left at the discretion of the laboratory,
that location must be close to the average thickness of the track as a whole.
*For the purposes of testing, the first radius is defined as 10m to 100m, the back straight as 110m to 200m, the final radius as 210m to 300m, and the main straight as 310m to 400m.
If the area of synthetic surface is exceptionally large (for example 10- or 12-lane straights), any necessary additional tests shall be at locations selected by the test laboratory.
At each location, the temperature of the surface shall be measured with a needle temperature probe and recorded. Each test position shall be recorded on a plan of the facility with the results recorded in the report.
Note: If the surface temperature is outside the permitted range of 10°C to 40°C, temperature correction of the results may be employed on the basis of interpolation from laboratory results as described in the first paragraph. If no graph is available then testing outside the surface temperature range shall not be undertaken. However, it is sometimes possible to avoid the need for this, by conducting the testing at a different time of day. For instance, if the facility is in a hot region, testing early in the morning or in the evening can result in the surface temperature falling to within the
above range.