DEVELOPED by US gymnast George Nissen in the late 1930s, trampolining has been taken up in many parts of the world, and world championship contests have been held since 1964. This form of gymnastic exercise is performed on a large, rectangular, canvas or elastic-webbing bed fastened to a padded metal frame. The trampoline enables a performer to continue springing upward by rebounding off its bed, performing acrobatic stunts while in flight. Competitive routines, after a number of preparatory bounces, consist of 10 to 12 contacts, on each of which a stunt is performed. Judging is similar to that in conventional competitive gymnastics. One of the most difficult tricks is the triple-twisting, double back somersault. The Sun-Sportathlon Sports Centre offers a number of five-day summer courses on gymnastics and trampolining for those between the ages of three and 14. Each new course starts every Monday and ends on Friday. There is also a term course in trampolining this September. Further details about the course fee, duration and eligibility will be announced by the Sun-Sportathlon (tel: 699-0482) at the end of this month. The fee for courses held at the French International School ranges from $380 to $420 a week while courses held at University of Hong Kong range from $320 to $380 a week.