Explaining the hip adduction moment variability during gait: Implications for hip abductor strengthening.

Background: There is emerging interest in hip abductor function during gait and its potential relationship to knee joint pathology. During gait, the hip abductor muscles are primarily responsible for generating moments of force to control frontal plane movement. The current study investigated the relationship between hip abductor muscle function and frontal plane hip moments of force during gait.

Methods: Frontal plane hip moments of force and electromyographic features of gluteus medius were measured during walking in 22 healthy individuals. Hip abductor strength, subject anthropometrics and gait velocity were recorded. Multiple regression models were used to evaluate the relationship between the anthropometric, velocity, strength and electromyographic variables and the initial and mid-stance magnitude of the hip adduction moment.

Findings: A positive relationship was found between the initial peak moment (Nm), and both body mass and gait speed (R(2)=90%). Body mass (positive) and hip abductor strength (negative) explained significant levels of mid-stance magnitude variability (R(2)=62.5%). Gait speed (positive) explained significant levels of variability in the normalized initial peak moment (Nm/kg) (R(2)=52%). No variables were included in the normalized mid-stance moment model (P>0.05).

Interpretation: Body mass was the key factor associated with high hip adduction moments during initial and mid-stance of the gait cycle. Increased gait velocity was associated with higher initial peaks and higher muscle strength was associated with lower mid-stance magnitude of the external hip adductor moment during walking. These findings suggest that in a healthy adult population, hip abductor strength and activation were not directly related to the hip adduction moment magnitude during gait.