Sagittal Plane Trunk Posture Influences Patellofemoral Joint Stress During Running

STUDY DESIGN: Cross-sectional, repeated-measures. OBJECTIVES: To examine the association between sagittal plane trunk posture and patellofemoral joint (PFJ) stress, and to determine whether modifying sagittal plane trunk posture influences PFJ stress during running. BACKGROUND: Patellofemoral pain is the most common injury among runners and is thought to be the result of elevated PFJ stress. While sagittal plane trunk posture has been shown to influence tibiofemoral joint mechanics, no study has examined the influence of trunk posture on PFJ kinetics. METHODS: Twenty-four asymptomatic recreational runners (12 women, 12 men) ran overground at a speed of 3.4 m/s under 3 trunk-posture conditions: self-selected, flexed, and extended. Trunk and knee kinematics, ground reaction forces, and electromyographic signals from selected lower extremity muscles were obtained. A previously described PFJ biomechanical model was used to quantify PFJ stress. RESULTS: The mean +/- SD trunk flexion angles under the self-selected, flexed, and extended running conditions were 7.3 degrees +/- 3.6 degrees, 14.1 degrees +/- 4.8 degrees, and 4.0 degrees +/- 3.9 degrees, respectively. A significant inverse relationship was observed between mean trunk flexion angle and peak PFJ stress during the self-selected condition (r = -0.60, P = .002). Peak PFJ stress was significantly lower in the flexed condition (mean +/- SD, 20.2 +/- 3.4 MPa; P < .001) and significantly higher in the extended condition (23.1 +/- 3.4 MPa; P < .001) comparedt the self-selected condition (21.5 +/- 3.2 MPa). CONCLUSION: Sagittal plane trunk posture has a significant influence on PFJ kinetics during running. Incorporation of a forward trunk lean may be an effective strategy to reduce PFJ stress during running.