SYMMETRY OF GROUND REACTION FORCE MEASURES IN SUCCESSIVE FOOTFALLS DURING RUNNING

Historically ground reaction forces have taken pl'ace using a single force platform during running. Dainty and Norman (1987) stated that force platforms must be designed to accommodate foot contact with a minimum necessity of targeting the platform. Such statements are verified by differences in ground reaction force variables when a subject has to alter their stride pattern on the approach to the plate. Differences have been primarily evident during the impact phase for both walking and running (Ohallis, 2001). The alteration of these kinetic variables was related to modification of lower limb angles at contact with the platform (Challis, 2001). It can be concluded that targeti ng of the force platform in gait analysis would produce kinetic measures that are not representational, or typical of subjects standard foot contact pattern. Many of the problems of targeting can be eliminated by sound experimental procedures, such as adequate approach and run-off distances, clear verbal instructions, and ensuring the subject maintains optical focus away from the platform surface. In addition, it is possible to measure footstrikes on more than one force platform. Providing the sUbject has no major biomechanical' deficit, or injury at the time of testing, measurement of successive footstrikes should not yield ground reaction force differences in normal walking or running (Dyson and Janaway, 2000). However, recent results in running (Smith et ai., 2004) revealed vertical impact loading rate and braking forces to be greater on the second of two successive footstrikes in soccer players. It was proposed this result could be attributed to increased muscular development on the SUbjects preferred r1imb. The aim of the current investigation is to assess the symmetry of successive footstrikes during running, with a secondary aim of investigating differences in force between the preferred and non-preferred limb