Hmm. Are we talking a high canopy, and fairly level ground? I feel like I'd definitely break an ankle if I tried sprinting otherwise.
I never had too much trouble, but sometimes things hiding in tall grass would surprise me, and in heavily treed patches I'd occasionally hit a low branch I didn't notice.
I also have to account for the fact that there was some light pollution, and I could always see skyglow from towns in the distance. I doubt land ever gets close, prehistoric or not, but in the darkest conditions that happen at sea apparently you can't see your own hands.