The effect of trunk and shank position on the hip-to-knee moment ratio in a bilateral squat.

OBJECTIVES: The effect of knee position on joint moments during squats has been studied; however, the effect of trunk angle has been less well investigated. This study evaluated the effect of both trunk and knee sagittal plane position on the distribution of moments between the hip and knee extensors during the bilateral squat. DESIGN: Observational study. SETTING: Biomechanics laboratory. PARTICIPANTS: One hundred individuals performed bilateral squats. MAIN OUTCOME MEASURES: Motion and force data were collected using motion capture and force plates. Trunk and shank angles and hip and knee moments were calculated. A linear regression was used to associate the ratio between the hip and knee moments (hip-to-knee moment ratio) with the sagittal plane trunk and shank angles, while accounting for six squat depths (between 60° and 110° of knee flexion) and side. RESULTS: Trunk angle and shank angle each contributed to the hip-to-knee moment ratio (P < .001) with trunk accounting for a higher proportion of variance than the other variables. The hip-to-knee moment ratio increased with increasing trunk angle and with decreasing shank angle. CONCLUSIONS: This large cohort study supports the use of trunk position to instruct squat technique with the goal of modifying hip and knee moments.

Individuals With Pre-arthritic Hip Pain Walk With Hip Motion Alterations Common in Individuals With Hip OA.

Background: Individuals with hip osteoarthritis (OA) commonly walk with less hip extension compared to individuals without hip OA. This alteration is often attributed to walking speed, structural limitation, and/or hip pain. It is unclear if individuals who are at increased risk for future OA (i.e., individuals with pre-arthritic hip disease [PAHD]) also walk with decreased hip extension. Objectives: (1) Determine if individuals with PAHD exhibit less hip extension compared to individuals without hip pain during walking, and (2) investigate potential reasons for these motion alterations. Methods: Adolescent and adult individuals with PAHD and healthy controls without hip pain were recruited for the study. Kinematic data were collected while walking on a treadmill at three walking speeds: preferred, fast (25% faster than preferred), and prescribed (1.25 m/s). Peak hip extension, peak hip flexion, and hip excursion were calculated for each speed. Linear regression analyses were used to examine the effects of group, sex, side, and their interactions. Results: Individuals with PAHD had 2.9° less peak hip extension compared to individuals in the Control group (p = 0.014) when walking at their preferred speed. At the prescribed speed, the PAHD group walked with 2.7° less hip extension than the Control group (p = 0.022). Given the persistence of the finding despite walking at the same speed, differences in preferred speed are unlikely the reason for the reduced hip extension. At the fast speed, both groups increased their hip extension, hip flexion, and hip excursion by similar amounts. Hip extension was less in the PAHD group compared to the Control group (p = 0.008) with no significant group-by-task interaction (p = 0.206). Within the PAHD group, hip angles and excursions were similar between individuals reporting pain and individuals reporting no pain. Conclusions: The results of this study indicate that kinematic alterations common in individuals with hip OA exist early in the continuum of hip disease and are present in individuals with PAHD. The reduced hip extension during walking is not explained by speed, structural limitation, or current pain.

Hip and Trunk Muscle Activity and Mechanics During Walking With and Without Unilateral Weight.

Pelvic drop is caused by decreased hip abductor muscle activity and is associated with lower-extremity injury. Hip abductor strengthening exercises are well established; however, no standard method exists to increase hip abductor activity during functional activities. The purpose of this research was to study the effects of walking with a unilateral weight. A total of 26 healthy adults walked on an instrumented treadmill with and without handheld weight (15%-20% body weight). Muscle activity, kinematic, and kinetic data were collected using surface electromyography, motion capture, and force plates, respectively. Average hip and trunk muscle activity, hip, pelvic, and trunk angles, and peak internal hip moments during stance were compared for each side (contralateral/ipsilateral to the weight) between conditions (unweighted/weighted) using a generalized linear model with generalized estimating equation correction. Interactions between condition and side were observed for muscle activity, frontal plane pelvic and trunk angles, and frontal plane hip moments (P ≤ .003). Compared with the unweighted condition, the weighted condition had higher hip abductor activity contralateral to the weight (P < .001), while no change was found ipsilateral to the weight (P ≥ .790). Similar changes were found for kinematic and kinetic variables. Walking with a unilateral weight may be a therapeutic option to increase functional hip abductor activity.