PATELLOFEMORAL JOINT COMPRESSIVE FORCES IN FORWARD AND BACKWARD RUNNING

The use of backward running is becoming more common in the rehabilitat ion setting. In particular, backward running has been suggested as a t reatment modality in patients experiencing patellofemoral pain syndrom e. To date, no study has examined the loads at the patellofemoral join t during backward running. The purpose of this study was to compare pa tellofemoral joint compressive forces during forward and backward runn ing. Ground reaction force and kinematic data were collected on five m ale joggers during free speed forward and backward running. A floor re action force vector model was used to calculate the stance phase knee extension moments. The distance used for the extensor muscle lever arm was 4.9 cm. Patellar mechanism angle was calculated based on knee joi nt angle. There was a reduction in the peak patellofemoral joint compr essive forces in backward compared with forward running (2277 +/- 192N vs. 4253 +/- 1292N; p < 0.05) at self-selected speeds. Peak patellofe moral joint compressive force occurred significantly later (p < 0.05) in the stance phase of backward running (52 +/- 4%) than in forward ru nning (35 +/- 3%). The peak patellofemoral joint compressive force nor malized io subject body weight was 5.6 +/- 1.3 body weight in forward running and 3.0 +/- 0.6 body weight in backward running. The results s uggest that backward running at a self-selected speed may reduce patel lofemoral joint compressive forces and, coupled with the quadriceps st rengthening that has previously been reported, may be beneficial in th e rehabilitation of patellofemoral pain syndrome in runners. However, constant speed comparisons or other models may yield different results .