Their skulls and necks would eventually resemble those of our primitive ancestors.

First the most obvious: the neck. Since individuals with frail necks who cannot bang their heads for hours are sexualkly unattractive, broader vertabrae would drive evolution to produce stronger necks. These also provider broader spaces for stronger tendons to attach to the bones. These are absolutely nessecary to prevent disk herniation into old age.

Now to the skull: The constant oscillating of the skull puts preasure on the soft and squishy brain. Their skulls would eventually resemble those of woodpeckers: The bone structure is much thicker and sponge-like to cushion the brain.

Notably, the woodpecker's brain is surrounded by thick, platelike spongy bone. At a microscopic level, woodpeckers have a large number of trabeculae, tiny beamlike projections of bone that form the mineral "mesh" that makes up this spongy bone plate. These trabeculae are also closer together than they are in the skylark skull, suggesting this microstructure acts as armor protecting the brain.

Since headbangig pushes the brain alternatingly against the front and back of the skull, These are the parts that are most reinforced. The skull would get a slightly more oval form.

Such an rather oval skull could provide an opportunity for an alternative headbanging mechanism: by tendon tension. There is enough room on the posterior skull to attach thick, strong tendons, just like in the legs. And just like with running, they store the kinetic energy of the skull falling forward and pull it back like a rubber band without needing to excert all the energy with muscles alone. The conservation of energy would probably be an evolutionary advantage, so the metalheads would actually loose their broad necks.

The eyes (or more precisely the eye sockets) would also become slightly more prominent. If headbanging constitutes most of your social interactions, you cannot let your eyes blindly stare into nothing until you're done. The eyes have to follow the back-and-forth movement constantly and the corresponding muscles are trained from early age, eventually taking up more space in the skull.

Their skulls and necks would eventually resemble those of our primitive ancestors.

First the most obvious: the neck. Since individuals with frail necks who cannot bang their heads for hours are sexually unattractive, broader vertebrae would drive evolution to produce stronger necks. These also provider broader spaces for stronger tendons to attach to the bones. These are absolutely nessecary to prevent disk herniation into old age.

Now to the skull: The constant oscillating of the skull puts preasure on the soft and squishy brain. Their skulls would eventually resemble those of woodpeckers: The bone structure is much thicker and sponge-like to cushion the brain.

Notably, the woodpecker's brain is surrounded by thick, platelike spongy bone. At a microscopic level, woodpeckers have a large number of trabeculae, tiny beamlike projections of bone that form the mineral "mesh" that makes up this spongy bone plate. These trabeculae are also closer together than they are in the skylark skull, suggesting this microstructure acts as armor protecting the brain.

Since headbangig pushes the brain alternatingly against the front and back of the skull, These are the parts that are most reinforced. The skull would get a slightly more oval form.

Such an rather oval skull could provide an opportunity for an alternative headbanging mechanism: by tendon tension. There is enough room on the posterior skull to attach thick, strong tendons, just like in the legs. And just like with running, they store the kinetic energy of the skull falling forward and pull it back like a rubber band without needing to excert all the energy with muscles alone. The conservation of energy would probably be an evolutionary advantage, so the metalheads would actually loose their broad necks.

The eyes (or more precisely the eye sockets) would also become slightly more prominent. If headbanging constitutes most of your social interactions, you cannot let your eyes blindly stare into nothing until you're done. The eyes have to follow the back-and-forth movement constantly and the corresponding muscles are trained from early age, eventually taking up more space in the skull.