Originally Posted by
hamster
I'm purely speculating, but, since Shermer's neck happens to people with extensive LD backgrounds, neck probably does not get strengthened (or at least not enough) through normal use, and simply adding weights to the helmet probably won't achieve much.
I'd look into specialized neck extension exercises. Some gyms even have neck extension / cervical extension machines. Two muscles involved are splenius cervicis and upper trapezius. The only way to target splenius cervicis is directly through neck extension (tilting the head back to look at the ceiling, against some sort of resistance). Upper trapezius is worked with shoulder press machines. (If you don't have a gym membership, "shrugging" while holding weights in your hands would do the job. Weights should be adjusted to achieve exhaustion after 8-10 reps.)
Intended for a slightly different issue, but I had a physio prescribe the following for various neck muscles -- basically, every so often when sitting at a desk, place my hand on my head and try to push my head into it (holding the hand steady so that my head stays upright). Multiple positions -- hand (or both hands clasped) on back of head, trying to tip back, hand on forehead, trying to tip forward, hand on cheek and do a set of tip sideways and a set of turn sideways. These aren't heavy-weight exercises, but I do feel like I've increased strength. (I have a fair bit of shoulder and neck pain from being a software engineer and having a slouching habit, but so far long-distance riding doesn't make it worse -- doesn't make it better, but doesn't make it worse, which is good enough for me. 400K is my max so-far, though.)