Biomechanical loads during common rehabilitation exercises in obese individuals

Abstract

Background: Squats and lunges are commonly prescribed rehabilitation exercises used to improve performance across a wide spectrum of patient populations. However, biomechanical studies have mainly examined young, normal weight populations performing these exercises at a difficulty level potentially too challenging for obese individuals. Understanding how obesity and different levels of difficulty affect lower extremity biomechanics could help to inform rehabilitation approaches used for obese individuals.

Purpose: The purpose of this study was to analyze and compare the lower extremity kinematics and kinetics in obese and normal weight females during performance of progressively more difficult squat and lunge exercises.

Study design: Cross-sectional study design.

Methods: Ten obese females (mean age, 37.4 years; BMI 39.2 ± 3.7 kg/m(2)) and ten normal-weight, age-matched female controls (38.1 years, BMI < 23 kg/m(2)) volunteered for the study. Each group performed two exercises, each in three different iterations: squatting at three standardized knee angles (60°, 70°, and 80°) and lunging at three standardized distances (1.0, 1.1, and 1.2 times tibial length). Three dimensional motion analysis using infrared markers and force plates was used to calculate range of motion as well as hip, knee, ankle and support moments (normalized for body weight). A repeated measures ANOVA model was used to determine between and within group differences.

Results: Support moments were higher in obese females for squat 70° (p=0.03) and 80° (p=0.01). Ankle extensor moments were higher in obese females for squat 80° (p=0.04). During lunge at all levels (1.0, 1.1, and 1.2), hip extensor moments were higher in obese subjects (p=0.004, 0.003, and 0.007 respectively). Within group, the support moments were significantly higher during squat 80° than squat 60° (p=0.01) in obese females. A non-linear relationship was found between hip moments and BMI during squat 60°, 70°, and 80°.

Conclusion: During two commonly prescribed rehabilitation exercises (squat and lunge), there were significantly greater support moments in obese individuals compared to normal controls. The non-linear associations between kinetic and anthropometric measures make the assessment of how best to approach exercise in obese individuals challenging.

Level of evidence: Level 3.

Keywords: Biomechanics; lunge; obesity; physical therapy; squat.

Figure 1.

The skeletal model of an obese female subject during squat exercise (left), placement of markers (center) and lunge exercise (right)

Figure 2.

The support moments between squat 80° were greater (*) than squat 60° in obese subjects (p = 0.01). No differences were seen for normal weight subjects

Figure 3.

For the lunge, hip extensor moments were greater (*) in obese than normal weight subjects for level 1, 1.1 and 1.2 (p‐values: 0.004, 0.003 and 0.007 respectively)

Figure 4.

Relationship between peak hip extensor moments for obese and normal weight subjects for squat 60°. The non‐linear polynomial fit showed a moderate relationship between hip moments and BMI