The optimal striking zone for groundstrokes is between waist and shoulder height. The diagram below shows that even at the age of 10-and-under, the regular Yellow ball will rebound above the head of an average 10-year-old player. This means that playing with efficient, realistic technique and tactics is very difficult, as players either have to:
- regularly take the ball early and play most groundstrokes above the optimal striking zone (in line with, and above the head), and / or
- play far behind the baseline and take the ball late, waiting for the ball to drop
The diagram above highlights the average heights (UNESCO, 2002) and the rebound height of the different balls (ITF, 2012). The rebound heights, as shown in the diagram, are official rebound heights as tested by the ITF:
- Red ball (Felt or Foam) - 85-105cm
- Orange ball -105-120cm
- Green - 120-135cm
- Yellow - 135-147cm
The slower Red, Orange and Green balls however are designed to bounce lower (and move through the air slower) to suit the height and motor skills of the player. This of course applies to wheelchair players of this age too. The video from Tennis Australia (above right) shows the varying ball rebound heights as the balls cross the net, compared to the regular Yellow ball.
For more details regarding the rebound heights of the slower Red, Orange and Green balls, please click here to access Appendix VI ITF Rules of Tennis or to view the full ITF Approved Tennis Balls, Classified Surfaces & Recognised Courts 2012 - a guide to products and test methods, click here.
Lifespan of the balls
As with the regular Yellow tennis balls, the slower stage balls also need replacing on a regular basis over a period of time.
The ITF, in consultation with the Tennis Industry recommend that the slower balls, when used for coaching purposes, last about three times longer than a regular Yellow tennis bal. The ITF recommend that the the slower stage balls are replaced after every 90-days, compared to the current Tennis Industry recommendation of 30-days for the regular Yellow balls.
For Red, Orange and Green stage competitions, the ITF recommend that the balls supplied at the start of each competition are new.
From 2014, the technical specifications for the Green stage 1 ball will change and implemented by all Tennis Industry manufacturers. As agreed by the Tennis Industry Association and the ITF, the following will be implemented:
- All Green balls would be produced in one Yellow colour with a Green dot to signify the type of ball. From 2014, it will not be possible to have 2 colour Green balls and be ITF approved
- All Green balls should be in sealed cans or cardboard boxes, rather than polybags or nets.
- Pressurised Green balls should be in pressurised cans
For more details please see Green Ball Rule Changes.