Relative mRNA expression of myosin heavy chain slow isoform (Myh7, panel A), SERCA2 (Atp2a2, panel B), parvalbumin (Pvalb, panel C), mitofusin 1 (Mfn1, panel D), mitofusin 2 (Mfn2, panel E), mitochondrial dynamin-like GTPase (Opa1, panel F) in the slow part of the medial gastrocnemius (MGS) after 2, 4 and 8 weeks of endurance training. Data are presented as mean + SD normalized by the reference gene (Hprt1). One-sided p-value represents the statistical significance of the training period (2, 4 or 8 weeks) with respect to the control group (Dunnett’s post hoc test) (S10 File). The symbols * denote values significantly different: * p < 0.05, ** p < 0.01, *** p < 0.001.