EHHADH and hydrops fetalis: Several studies reported a diminished succinate dehydrogenase, citrate synthase, and 3-hydroxyacyl-CoA dehydrogenase in HF group compared with CON, suggesting a decrease in aerobic oxidative enzyme activity of their skeletal muscle (see Supplementary material online, Table S3).5,9,10,13 Importantly, the elegant study by Mettauer et al. 9 noted that muscular oxidative capacity (Vmax) is decreased in HF compared with active CON, with no significant difference between sedentary CON and HF, suggesting that these differences may be mediated by physical activity rather than HF condition itself.