Most common secondary structure of protein Myosin in muscle and α...

Myosin in muscle and $\alpha$-keratin in hair are examples of fibrous proteins.

The most common secondary structure in both of these proteins is the $\alpha$-helix.

In $\alpha$-keratin, the polypeptide chains are coiled into a right-handed $\alpha$-helix.

Similarly, the tail region of myosin consists of two $\alpha$-helices coiled around each other to form a coiled-coil structure.

Thus, both proteins predominantly exhibit an $\alpha$-helical secondary structure.

Answer: both $\alpha$-helical