This is the second article in a series that will explain the most commonly used methods to evaluate sport surfaces. This article outlines the methods used to evaluate the Vertical Ball Rebound properties of a sport surface.This method is valid in both laboratory and field settings. It is utilized for the sports of basketball, field hockey, and soccer, but this article focuses on its use in multi-sport and basketball surfaces.
Vertical Ball Rebound represents the rebound height produced on the sports surface as a percentage of the rebound height produced on concrete. As with Force Reduction, there has been significant harmonization of this test across standardization bodies, athletic associations, and manufacturing associations. The same test will yield vertical ball rebound results for DIN 18032-2, EN 14904, and ASTM F2772. The EN/ASTM tests yield identical numerical results and are used by the MFMA™(Maple Flooring Manufacturer’s Association) as well as FIBA™ (International Basketball Federation). Values computed using the DIN standard will generally be 1-2% higher than those computed using the other methods. This is because DIN 18032-2 considers the top of the ball to be the rebound height, while ASTM and EN consider the bottom of the ball to be the rebound height, and this causes slight differences in the calculated percentages.
This standard has been in place since at least the mid 1980’s. The developers decided that rather than specifying the pressure in the ball, they would specify how high the ball should rebound on concrete. This indirectly sets the pressure in the ball, and is probably more accurate than using a pressure gauge. Most standards (EN, ASTM, MFMA and FIBA) require that the ball generate a rebound of 1.05 m +/- 0.025m (41″ +/- 1″) on concrete or an equally hard reference surface. DIN 18032-2 simply measures to the top of the ball instead of the bottom and thus it requires 1.3m +/- 0.025m (51″ +/- 1″) when dropped on concrete. The rebound on the sports surface is then measured and expressed as a percentage of the rebound on concrete (Reb = Hfloor/Hconcrete*100%). Higher rebound values indicate rebound levels that are closer to concrete.
Force Reduction and Ball Rebound are generally related. As a floor becomes harder the Ball Rebound will increase as the Force Reduction decreases. Likewise as a floor becomes softer the Ball Rebound will decrease as the Force Reduction increases. The DIN, ASTM and EN standards require a rebound of 90% or more. FIBA and the MFMA are a bit more strict and require a rebound of 93% or more.
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There are a number of topics related to ball rebound that could not be covered in a short article. Future articles will address items such as inflation pressure, field testing, dead-spots, and limitations of this test method.
Notes:
- It is not uncommon for certain floors to produce rebound levels that exceed 100% using this method. These floors often have a force reduction value of between 25% and 40%.
- A followup article discussing the effects of pressure as well as some of the limitations regarding this method is being developed.
- Our most common field test request revolve around the presence or perception of dead-spots. This method is the basis behind our dead-spot evaluation and severity assessment. Dead-spots will be explored later but until then we have found that rebound height as measured by this test does not correlate to perceived dead-spots. Our brains process a wide variety of inputs during a rebound or dribble activity (sound, vibration, height) and when any of these things differs it seems as though we perceive this difference as a difference in rebound height. Many points perceived as dead-spots produce ball rebound levels above those required by international standards.
