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

•No study has examined the “fat-but-fit” paradigm when considering muscular strength.•There was no difference in CRP between normal weight and unfit vs. overweight and fit participants.•Overweight fit adults had a lower hazard rate compared to unfit normal weight adults.•Adequate fitness (determined by strength) may attenuate inflammation and prevent premature mortality among overweight adults.

BackgroundNo 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.PurposeTo examine the relationship between lower extremity muscular strength, C-reactive protein (CRP), and all-cause mortality among normal weight, overweight and obese individuals.MethodsData 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.ResultsIndependent of physical activity and other confounders, compared to those who were normal weight and unfit, unfit overweight (β = .14, p = 0.009), unfit obese (β = .33, p < 0.001), and obese and fit (β = .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 (β = 0.04, p = 0.35). Compared to normal weight unfit adults, overweight fit (HR = 0.28; 95% CI: 0.11-0.70; p = 0.008) adults had a lower hazard rate for all-cause mortality.ConclusionsThese finding suggest that increased lower body strength, independent of physical activity, may reduce premature all-cause mortality and attenuate systemic inflammation among overweight adults.