Obesity and female sex are independent risk factors for knee osteoarthritis and also influence gait mechanics. However, the interaction between obesity and sex on gait mechanics is unclear, which may have implications for tailored gait modification strategies.
The purpose of this study was to examine the influence of obesity and sex on sagittal and frontal plane knee mechanics during gait in young adults.
Forty-eight individuals with (BMI = 33.03 ± 0.59; sex:50 % female; age:21.9 ± 2.6 years) and 48 without obesity (BMI:21.59 ± 0.25; sex:50 % female; age:22.9 ± 3.57 years) matched on age and sex completed over-ground gait assessments at a self-selected speed. Two (BMI) by two (sex) analysis of variance was used to compare knee biomechanics during the first half of stance in the sagittal (knee flexion moment [KFM] and excursion [KFE]) and frontal plane (first peak knee adduction moment [KAM], knee varus velocity [KVV]).
We observed a BMI by sex interaction for normalized KFM (P = 0.03). Females had smaller normalized KFM compared to males (P = 0.03), but only in individuals without obesity. Males without obesity had larger normalized KFM compared to males with obesity (P = 0.01), while females did not differ between BMI groups. We observed main effects of sex and BMI group, where females exhibited greater normalized KAM (P < 0.01) and KVV (P < 0.01) compared to males, and individuals with obesity walked with greater KVV compared to those without obesity (P < 0.01). All absolute joint moments were greater in individuals with obesity (all P<0.01) and males had greater absolute KFM compared to females (P < 0.01).
We observed sex differences in gait mechanics, however, KFM differences between males and females were only evident in individuals without obesity. Further, females and individuals with obesity had a larger KAM and KVV, which may contribute to larger medial compartment joint loading.

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