Relative Strength at the Hip, Knee, and Ankle Is Lower Among Younger and Older Females Who Are Obese

BACKGROUND AND PURPOSE The mobility of individuals who are obese can be limited compared with their healthy weight counterparts. Lower limb strength has been associated with mobility, and reduced strength may contribute to mobility limitation among individuals who are obese. However, our understanding of the effects of obesity on lower limb strength is limited. The purpose of this study was to investigate the effects of obesity and age on extension and flexion strength at the hip, knee, and ankle. METHODS Using a cross-sectional design, 10 younger (18-30 years) healthy weight (body mass index = 18-24.9 kg/m), 10 younger obese (body mass index >30 kg/m), 10 older (65-80 years) healthy weight, and 10 older obese female participants performed isokinetic maximum voluntary contractions in ankle plantar flexion (PF), ankle dorsiflexion (DF), knee extension (KE), knee flexion (KF), hip extension (HE), and hip flexion (HF). RESULTS AND DISCUSSION Absolute strength among obese participants was 29% higher in DF (P = .002), 27% higher in KE (P = .004), and 23% higher in HF (P = .001), compared with healthy weight participants. Strength relative to body mass among obese participants was 31% lower in PF (P < .001), 14% lower in DF (P = .042), 16% lower in KE (P = .015), 27% lower in KF (P < .001), 29% lower in HE (P < .001), and 19% lower in HF (P = .001). CONCLUSIONS Obese females exhibited lower relative strength at the ankle and hip, similar to the lower relative strength exhibited at the knee. Obese females also exhibited higher absolute strength, but only for 3 of 6 lower limb exertions investigated. This lack of uniformity across the 6 exertions is likely due to the still unclear underlying biomechanical mechanism responsible for these strength differences, which may also be influenced by aging. The effects of obesity on lower limb strength were also generally consistent between the 2 age groups investigated.