Long-term impact of adherence to muscle-strengthening guidelines on inflammation markers: a 17-year follow-up study with obesity parameters as mediators

Objective To evaluate the relationship between adherence to muscle-strengthening guidelines in young adulthood and inflammation markers over a 17-year follow-up period. Additionally, it aims to examine whether body mass index (BMI) and waist circumference (WC) act as mediators in this relationship. Methods The study analysed data from young adults aged 18-26 years who participated in waves III (2001-2002), IV (2008-2009) and V (2016-2018) of the Add Health Study. Adherence to muscle-strengthening guidelines was self-reported, and participants were classified as adherent if they engaged in strength training ≥2 days per week across all waves. Venous blood samples were collected at participants' homes to measure high-sensitivity C reactive protein (hs-CRP) levels and various cytokine concentrations, including interleukin (IL)-6, IL-1beta, IL-8, IL-10 and tumour necrosis factor-alpha (TNF-α). A global inflammation score was also calculated using z-scores of these markers. Results A total of 2320 individuals participated (60.8% females). Participants adhering to muscle-strengthening guidelines exhibited significant reductions in hs-CRP, IL-6 and the inflammation z-score, with mean difference (MD) of -1.556 mg/L (95% CI BCa -2.312 to -0.799), -0.324 pg/mL (95% BCa CI -0.586 to -0.062), and -0.400 (95% BCa CI -0.785 to -0.035), respectively. Mediation analysis revealed that BMI and WC levels at wave V significantly mediated the relationship between strength training and inflammation z-score, with significant indirect effects of -0.142 (95% CI -0.231 to -0.055) for BMI and -0.210 (95% CI -0.308 to -0.124) for WC. Conclusion Adherence to muscle-strengthening guidelines alone may not be sufficient to achieve a notable decrease in inflammation without concurrent reductions in these obesity parameters.