Lower extremity strength, systemic inflammation and all-cause mortality: Application to the "fat but fit" paradigm using cross-sectional and longitudinal designs

Background: No study has applied the "fat-but-fit" paradigm with respect to muscular strength as an index of fitness, despite muscular strength being independently associated with functional ability and mortality. Purpose: To examine the relationship between lower extremity muscular strength, C-reactive protein (CRP), and all-cause mortality among normal weight, overweight and obese individuals. Methods: Data from the 1999-2002 NHANES were used (N = 2740 adults; >= 50 years). CRP values were obtained from a blood sample. Lower body isokinetic knee extensor strength (IKES) was assessed using a Kin Kom MP isokinetic dynamometer. Participant data was linked to death certificate data from the National Death Index to ascertain all-cause mortality status. Participants were classified, based on body mass index (BMI) and strength as: normal weight and unfit (<75th IKES percentile); overweight and unfit; obese and unfit: normal weight and fit (>= 75th IKES percentile); overweight and fit; and obese and fit. Results: Independent of physical activity and other confounders, compared to those who were normal weight and unfit, unfit overweight (beta = .14, p = 0.009), unfit obese (beta = .33, p < 0.001), and obese and fit (beta = .17, p = 0.008) participants, had higher CRP levels. However, there was no difference in CRP levels between normal weight and unfit participants and overweight and fit participants (beta = 0.04, p = 035). Compared to normal weight unfit adults, overweight fit (HR = 028; 95% CI: 0.11-0.70; p = 0.008) adults had a lower hazard rate for all-cause mortality. Conclusions: These finding suggest that increased lower body strength, independent of physical activity, may reduce premature all-cause mortality and attenuate systemic inflammation among overweight adults. (C) 2015 Elsevier Inc. All rights reserved.