Objectives To compare patellofemoral joint (PFJ) stress between level, incline, and decline running. Design Experimental study. Setting University laboratory. Participants Twenty recreational runners. Main outcome measures Kinematics and kinetics of the trunk and lower extremity were obtained under 3 treadmill conditions: level, 6° incline, and 6° decline. PFJ stress, PFJ reaction force, and PFJ contact area were determined using a biomechanical model. One-way ANOVAs with repeated measures and post-hoc analyses were used to compare outcome variables across the 3 conditions. Results Peak PFJ stress and PFJ stress-time integral (cumulative PFJ stress over the stance phase) during decline running were significantly higher than during level and incline running. There was no difference in peak PFJ stress and PFJ stress-time integral between level and incline running. The increased peak PFJ stress during decline running was related to increased PFJ reaction force, resulting from a decrease in trunk flexion angle. Conclusions Running on a decline treadmill resulted in higher peak PFJ stress and stress-time integral. Peak PFJ stress and PFJ stress-time integral were similar during level and incline running. Results from this study may be used to prevent excessive PFJ stress during decline running, by targeting a postural strategy utilizing increased trunk flexion.
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