Abdominal fat distribution differently affects muscle strength of the upper and lower extremities in women

In obese subjects, reduced muscle mass and strength are associated with impaired functional and metabolic capacity. We therefore investigated the association between abdominal fat distribution, fat mass index and maximum muscle strength of upper and lower extremities in obese patients.

One hundred and fifty five outpatients with a body mass index (BMI)⩾30 kg/m² (105 women; 45.1±14.6 years; BMI 43.5±8.2 kg/m²) were included in the study. Grip and knee extension strength were measured with dynamometers. Using bioelectric impedance analysis, fat-free mass and fat mass indices (FFMI, FMI) were calculated. The influence of age, weight, FFMI, FMI and waist-to-hip ratio (WHR) on grip and knee extension strength was investigated in a risk factor-adjusted regression analysis.

BMI did not correlate with hand grip or knee extension strength. The regression model confirmed a positive effect of higher weight on strength parameters; however, increased FMI was shown to have a negative effect on strength in both sexes (women, knee: β: -1.495, confidence interval (CI): -2.075 to -0.0914, P<0.0001; women, hand: β: -0.714, CI: -1.156 to -0.273, P=0.002; men, hand: β:-1.448, CI: -2.618 to -0.278, P=0.016). Although increased WHR positively influenced knee extension strength (β: 24.286, CI: 0.728-47.844, P<0.043), it did not affect grip strength in women. This association was not seen in men.

Body fat distribution rather than BMI alone needs to be considered when evaluating strength parameters in obesity. As the relationship between obesity and strength of the upper versus lower extremities differs, grip strength cannot be considered an indicator of whole body strength in obese individuals.