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 highsensitivity C reactive protein (hs-CRP) levels and various cytokine concentrations, including interleukin (IL)−6, IL1beta, IL-8, IL-10 and tumour necrosis factor-alpha (TNFα). 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 −1.556mg/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.