What is the test for a jury to determine whether a motorcyclist's injuries constitute "great bodily injury"?

It is well settled that the determination of great bodily injury is essentially a question of fact, not of law. " 'Whether the harm resulting to the victim ... constitutes great bodily injury is a question of fact for the jury. [Citation.] If there is sufficient evidence to sustain the jury's finding of great bodily injury, we are bound to accept it, even though the circumstances might reasonably be reconciled with a contrary finding.' " (People v. Wolcott (1983) 34 Cal.3d 92, 107, 192 Cal.Rptr. 748, 665 P.2d 520, quoting People v. Salas (1976) 77 Cal.App.3d 600, 606, 143 Cal.Rptr. 755.) ³