The effect of obesity combined with low muscle strength on decline in mobility in older persons: results from the InCHIANTI Study

Objective: Both obesity and muscle impairment are increasingly prevalent among older persons and negatively affect health and physical functioning. However, the combined effect of coexisting obesity and muscle impairment on physical function decline has been little studied. We examined whether obese persons with low muscle strength experience significantly greater declines in walking speed and mobility than persons with only obesity or low muscle strength. Design: Community-dwelling adults aged >= 65 years (n = 930) living in the Chianti geographic area (Tuscany, Italy) were followed for 6 years in the population-based InCHIANTI study. Measurements: On the basis of baseline measurements (1998-2000), obesity was defined as body mass index (BMI) >= 30 kg/m(2) and low muscle strength as lowest sex-specific tertile of knee extensor strength. Walking speed and self-reported mobility disability (ability to walk 400m or climb one flight of stairs) were assessed at baseline and at 3-and 6-year follow-up. Results: At baseline, obese persons with low muscle strength had significantly lower walking speed compared with all other groups (P <= 0.05). In longitudinal analyses, obese participants with low muscle strength had steeper decline in walking speed and high risk of developing new mobility disability over the 6-year follow-up compared with those without obesity or low muscle strength. After the age of 80, the differences between groups were substantially attenuated. The differences seen in walking speed across combination of low muscle strength and obesity groups were partly explained by 6-year changes in muscle strength, BMI and waist circumference. Conclusions: Obesity combined with low muscle strength increases the risk of decline in walking speed and developing mobility disability, especially among persons <80 years old. International Journal of Obesity (2009) 33, 635-644; doi: 10.1038/ijo.2009.62; published online 21 April 2009