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

Abstract

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.