(a) Distribution of identified superfast muscles (SFMs, beige disks) in vertebrates relative to key evolutionary events: excitation-contraction coupling, and myosin heavy chain (MYH) gene evolution. Modified after (Bass, 2014). (b) Ranges of in vivo cycling frequency. SFM (labeled purple) has been defined as synchronous muscle capable of producing work at cycling frequencies in excess of 90 Hz (grey box) (Rome, 2006). Bat, songbird, and toadfish SFM approach or exceed 200 Hz. CT, cricothyroid; VTB, m. tracheobronchialis ventralis; EDL, m. extensor digitorum longus; SOL, soleus; VL, vastus lateralis.