Microgravity, which seems like zero gravity, but is actually a state of free-fall caused by a spacecraft's orbit around the Earth, has long been known to wreak havoc on the human body. Without having to support the weight of the body, bones begin to lose density and muscles atrophy, requiring astronauts to exercise regularly to stave off the effects. Without gravity to pull fluids downwards, astronauts often experience a phenomenon colloquially known as "puffy-face-chicken-legs syndrome". More recently, this increase in fluid around the brain has been linked to changes in astronauts' vision. Fluid shift has also been blamed for a diminished sense of smell and taste.