Feeling strong as the pale, flat light of dawn wears on, and the details start to resolve out of the landscape is a unique sensation, though it has to be said that if you're going to have a low time on a ride it will also generally be at this time, circadian rhythms being what they are. Riding at night involves an element of sleep deprivation, and knowing how this affects you, and what to do when you feel tired is a major part of the achievement of completing long Audax events. It is important to make the distinction between physical and mental fatigue. Physical fatigue involves wear and tear on the muscles and connective tissues, plus the heart and lungs, and tends to be very predictable. I embrace physical fatigue with pleasure as I know that after I have eaten and rested I will be even stronger.
Mental fatigue is much harder, linked as it is with mood and cognition.
Tackling the extreme forms is straightforward. Even the brightest dynamo lighting doesn't create that much contrast, so resolving the shapes throws more load on the processing power of the brain. There comes a point, if you cycle all through the first night, then into the second, when the road becomes indistinguishable from the verge, which is itself indistinguishable from the trees. The shape of the night sky through the trees takes on human form and swoops low to arrest you. The bike starts to wobble, and gear changes get inexplicably inaccurate.