A PORTABLE SET-UP FOR COLLECTING TRIPLE JUMP GROUND REACTION FORCES

Abstract

While GRFs have been commonly assessed during running and some jumping activities little is known about these forces during the t r i p l e jump. The purpose of t h i s study was t o design, build, and t e s t a portable t r i p l e jump runway t h a t could be used t o collect ground reaction f o r c e d a t a for a l l three takeoffs in succession. Previous studies have used only one or two p l a t e s . The portable runway was designed t o house t h r e e Bertec force p l a t e s and w a s b u i l t out of compressed ply wood. The force plate housing holes were spaced 3 meters (10 f e e t ) apart which can accommodate a minimum hop-step ratio of 3m:3m (10ft:lOft) . The runway was also designed so t h a t the sections housing the force p l a t e s can be 'telescoped' out in 30.48 cm (1 foot) increments. Given these incremental increases, the maximum hop-step r a t i o s possible are 4.52m:4.52m (15ft : E f t ) . Because the force plates were not rigidly mounted t o the ground, a number of precautions were taken t o eliminate possible measurement errors . In order t o eliminate sliding, the runway s t r u c t u r e was precision made so t h a t when the force plates were set into their housing, the bottom of the plates fit snugly against the walls of t h e s t r u c t u r e while I allowing the top p l a t e t o f l o a t f r e e l y . I n o r d e r t o I eliminate the possibility of rocking, a f l a t formica surface was placed under t h e p l a t e s . Both the floor and the formica I surface were tested with a leveler and determined to be f l a t . Testing of the portable forceplate setup was done using three Bertec force p l a t e s (40cm x 60cm) spaced using the minimum hop-step r a t i o s , 3m:3m. One subject performed 15 t r i p l e jumps (using a s i x step approach), each jump 9 meters t o t a l distance (3m:3m:3m) . This procedure is appropriate because t h i s is a typical practice session f o r the collegian female jumpers coached by the researcher. The f i n a l landing was onto gymnastics mats (not t y p i c a l ) . The studv showed that accurate ground reaction force data can be collected for the t r i p l e jump for a l l three takeoffs in succession. This type of setup would be very useful t o s c i e n t i f i c a l l y oriented coaches f o r use during p r a c t i c e sessions. It would also be useful for researchers interested in modeling ground r e a c t i o n f o r c e s in the t r i p l e jump. However,! it probably would not be useful for collecting data for jumps using a f u l l approach. The most noticeable finding r e l a t e d t o the force-time curves was t h a t each takeoff phase has its own c h a r a c t e r i s t i c force-time curve. This has not been completely documented in previous studies that used only one or two force plates.