Syndecan-4 is a transmembrane proteoglycan that regulates actin cytoskeleton, cell adhesion, and cell migration. Since actin is involved in muscle contraction, we have already investigated skeletal muscle function in syndecan-4 knockdown (SDC4) mice. Skeletal muscle performance was indeed reduced in SDC4 mice. Consequently, it is plausible to assume that mitochondrial functions are altered in SDC4 mice as well. Therefore, we investigated mitochondrial architecture and the key members of mitochondrial dynamics and regulator of mitochondrial calcium uptake MICU1 in syndecan-4 knockdown mice.