Inflammatory proteins and muscle strength in adolescents: the Avena study.

OBJECTIVES To examine the associations between inflammatory proteins and muscle strength and to determine whether this association varies between overweight and nonoverweight adolescents. DESIGN Cross-sectional study. PARTICIPANTS A total of 416 Spanish adolescents (230 boys and 186 girls) aged 13 to 18(1/2) years. MAIN EXPOSURES Muscle strength score was computed as the mean of the handgrip and standing broad jump standardized values. The adolescents were categorized as overweight (including obese) or nonoverweight according to body mass index. Body fat and fat-free mass were derived from skinfold thickness. OUTCOME MEASURES C-reactive protein, complement factors C3 and C4, ceruloplasmin, and prealbumin levels. RESULTS The results of the regression analysis showed that C-reactive protein, C3, and ceruloplasmin were negatively associated with muscle strength after controlling for sex, age, pubertal status, weight, height, socioeconomic status, and cardiorespiratory fitness. Moreover, C-reactive protein and prealbumin levels were associated with muscle strength in overweight adolescents after controlling for potential confounders, including body fat and fat-free mass. CONCLUSIONS Low-grade inflammation is negatively associated with muscle strength in adolescents. The patterns of these associations seem more relevant in overweight adolescents, suggesting that having high levels of muscle strength may counteract the negative consequences ascribed to body fat.