Relative Muscle Strength Is Associated With Obesity-induced Biomechanical Adaptations Of The Trunk During Sit-to- stand

Abstract

Obesity decreases relative skeletal muscle strength and alters biomechanics during daily activities such as rising from a chair. To date, the role of this decreased muscle strength in obesity-induced biomechanical alterations is unknown. PURPOSE: To determine the relationship between lower extremity skeletal muscle strength and biomechanics during sit-to-stand. METHODS: Nine obese (BMI 32.5 ± 2.5 kg/m2) young adults (age: 28.4 ± 5.7 y) completed sit-to-stand task three times from a chair (seat height: 52 cm). Ten high speed cameras were used to track retroreflective coordinate data through 3D motion analysis at a rate of 200Hz. Specific outcomes of interest included: peak trunk flexion velocity (deg/s), peak trunk flexion angle (deg), and task duration (s). Maximal voluntary isometric contractions (MVICs) of the knee extensors and flexors were measured via a previously validated handheld dynamometer (Hoggan MicroFET2) and normalized to body mass. Linear regression was used to determine relationships between body mass and relative muscle strength with independent variables. RESULTS: Body mass index was positively associated with peak trunk flexion velocity (y = 4.458x - 57.208, r2 = 0.506, p = 0.032), but not peak trunk flexion angle (p = 0.127) or task duration (p = 0.924). Conversely, relative knee extensor and knee flexor strength were inversely related to peak trunk flexion velocity and angle (r2 = 0.541 - 0.780, p < 0.05). The ratio of relative knee extensor to knee flexor strength was inversely related to task duration (y = -0.773x + 4.784 r2 = 0.553, p = 0.022). CONCLUSIONS: Excess body mass induces greater trunk flexion velocity, likely to generate sufficient momentum to stand. High levels of knee extensor and flexor strength may decrease peak trunk flexion angle and velocity reduce sit-to-stand time in obesity.