Impaired neuromuscular trunk control has been associated with lower extremity injuries, the incidence of which differs by gender. Whether neuromuscular trunk control differs by gender is unknown. PURPOSE: To determine gender differences in measures of neuromuscular trunk control during an unstable sitting task. METHODS: Thirty subjects (15 males, 15 females) completed five trials of an unstable sitting task. The unstable sitting apparatus consisted of a seat secured atop a 30 cm polycarbonate resin hemisphere outfitted with a foot support. Center of pressure (CoP) in the anterior-posterior (AP) and medial-lateral (ML) direction was recorded using a conductive force plate. To increase the likelihood of detecting subtle differences, we employed both linear and nonlinear measures for analysis. Linear measures were CoP sway velocity (SV), sway path (SP), and the 95% ellipse area (EA). Approximate entropy (ApEn) was used as a nonlinear measure to quantify the regularity of COP_AP and COP_ML fluctuations. Gender comparisons were made using five one-way ANOVAs with height and mass as covariates at an a priori alpha level of 0.05. RESULTS: Males and females were significantly different for the dependent variables of ApEn_ML, SV, SP, and EA (Table 1). There was no significant difference for ApEn_AP. CONCLUSION: During an unstable sitting task, females displayed lower CoP velocity, smaller CoP displacement, and greater regularity in CoP_ML fluctuations. Gender differences in trunk neuromuscular control may have a role in the greater incidence of lower extremity injury observed in females and warrant further exploration.Table 1: CoP measures during unstable sitting. Values represent adjusted means and standard errors.