Sex and body height influences on patellofemoral joint reaction force during stair ascent.

Background: Females are at greater risk of developing patellofemoral pain (PFP) than males, and an excessive patellofemoral joint reaction force (PFJRF) may contribute to this discrepancy. It is unknown if the PFJRF differs between males and females during stair ascent. Additionally, body height may also influence the PFJRF. This study investigated PFJRF differences between males and females and explored relationships between body height and PFJRF during stair ascent.
Methods: Thirty males (25.6 (2.7) yr) and thirty females (23.7 (2.2) yr) ascended stairs (96 steps/min). Three-dimensional kinematics (200 Hz) and kinetics (2000 Hz) were recorded and used to calculate biomechanical dependent variables.
Results: Females experienced a greater PFJRF magnitude (mean difference (MD) = 3.2 N/kg; 95% CI = 0.5, 5.9; p = 0.022) and rate (MD = 23.8 N/kg/sec; 95% CI = 2.7, 45.1; p = 0.029), quadriceps muscle force (3.1 N/kg; 95% CI = 0.2, 6.0; p = 0.036), and knee flexion angle (MD = 2.3°; 95% CI = 0.3, 4.3; p = 0.026). Females exhibited shorter quadriceps lever arm length (MD = -0.1 cm; 95% CI = -0.2, 0.0; p = 0.024) and body height (MD = -16.9 cm; 95% CI = -20.5, -13.2, p < 0.001) compared to males. Body height was inversely correlated with PFJRF magnitude (r = -0.31; p = 0.017), rate (r = -0.28; p = 0.032), and knee flexion angle (r = -0.54; p < 0.001).
Conclusion: Females experienced a greater PFJRF than males. Additionally, the PFJRF and body height were inversely correlated. This observed difference may contribute to the PFP sex discrepancy and be due, at least in part, to body height differences.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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