University of Virginia researchers say they’ve determined people’s physical condition affects how they view their environment.

The scientists investigated the impact of fatigue, physical ability, and potential bodily endangerment on how we perceive our environment. They found people have a natural tendency to view hills as steeper when they are tired, less physically able, or carrying a heavy load. Likewise, inclines appear greater and the distance to the ground appears farther when there is a perceived risk of injury.

The author of the study — psychology professor Dennis Proffitt — attributes that perceptual variance to the instinctive need to conserve energy and protect ourselves from harm.

The visually specified layout of the environment is modulated in perception in ways that promote effective, efficient, and safe behavior, said Proffitt.

The research is detailed in the journal Perspectives on Psychological Science.