Head-banging and the neck: what long-time fans work out
Head-banging is a physical activity that nobody trains for. People pick it up in a crowd, do it for hours at a time, and only think about the mechanics when something hurts. Fans who have been doing it for a long time almost all arrive at the same conclusions, and none of those conclusions is "stop".
Where the load goes
The movement is driven by a small group of muscles at the back and sides of the neck, working against the weight of the head and repeating the same arc without rest. Nothing about a single motion is extreme. The problem is the repetition, the speed set by the band rather than by the body, and the fact that the neck has no way to share the load the way a leg can shift weight to the other side.
Hair changes the physics. Long, heavy, wet hair adds mass at the end of the lever, and a hard whip with soaked hair asks a lot more of the neck than the same movement does dry. Anyone who has felt the difference between the first song and the encore knows this without being told.
What experienced fans change
They warm up. Not a routine, just a few slow rolls and side-to-side movements while the support act plays, so the first fast song is not also the first movement of the night.
They pace it. Head-banging every song of every set is how people finish a festival unable to turn their heads. Picking the songs worth it, and standing through the rest, is the single habit that separates a long night from a ruined week.
They use the hips and shoulders. A movement that starts in the upper body and travels through the neck is far less punishing than one the neck generates alone, and it looks better anyway.
They keep the arc reasonable. The full forward-and-back slam is the version that hurts; a smaller, tighter movement in time with the music carries the same energy without hanging the head out at the end of its range.
Signs to stop for the night
Stiffness the next morning is ordinary. Pain that arrives during the set is not, and neither is a headache that starts at the base of the skull, dizziness, a tingling or numb arm, or a neck that will not turn as far as it did an hour ago. Those are reasons to stand still and to see a professional if they do not settle — a message board, this page included, is not a substitute for one.
The risk people forget
Hearing takes more permanent damage at a show than the neck does, and it gives far less warning. Ringing after a gig is a sign that something has already happened. Filtered earplugs made for music keep the mix intact and cost very little next to the ticket, and the fans who have been going to shows the longest are, almost without exception, the ones wearing them.
None of this is an argument for holding still. It is an argument for being able to keep doing it for decades, which is what everyone in the front row says they want.