IIRC, that was to keep his head from falling over because he was so tired. Because in solo RAAM you are basically running with no or very little sleep. One would likely have similar sleep deprivation issues regardless of the type of bike.
Well firstly, the pic is of Shanna Armstrong who competed in one of the
female divisions.
She and quite a few other competitors improvised neck braces during RAAM as their neck muscles succumbed to the stress of long hours holding the head in an unnatural position.
If you want more info you should google a condition frequently encountered by (DF riding) ultra-marathoners - 'Shermer's Neck'.