To shed more light on the relationship between the health benefits of exercise and IBS, we evaluated cf-mtDNA levels before and after twelve weeks of moderate exercise and the activity of its endogenous counter-regulator, DNase I. Since the human DNASE1 gene is polymorphic, we genotyped the non-synonymous rs1053874 SNP, which is involved in the susceptibility to common diseases [34], in subjects under investigation. The gene discussed is DNASE1; the disease is irritable bowel syndrome.