|Picture from Flickr by runsociety.com|
After reading about optic flow, I guess I can say this is partly why running in the dark feels harder (other than me being terribly unfit after my fall). Optic flow is your visual sensation of moving through an environment. While running in the dark, you only see objects near to you. This is "fast" optic flow, in which scenery seems to be speeding by you quicker than normal.
As shown by researchers, optic flow can also affect estimation of distance ran. During a 5 km run with conditions of fast optic flow, the runners thought they'd ran 5 km when they had only covered 4.6 km. The take home message here is that in normal conditions (or slow optic flow), you will be able to run further for similar feelings of fatigue compared with night running (or fast optic flow).
Previous similar studies done on cyclists had similar results.
Remember this next time you're out riding or running when night falls. Something to remember especially if you're running the upcoming Sundown marathon which one of our staff did previously.
Parry, D and Micklewright, D (2014). Optic Flow Influences Perceived Exertion And Distance Estimation But Not Running Pace. Med and Sci in Sports Ex. doi: 10.1249/MSS.0000000000000257.