In 2011, a six-man crew completed a more than 500 day-long simulation to determine the psychological effects of a potential trip to Mars. Now, a study has been published showing that the crew members slept poorly and became increasingly sedentary as the mission progressed. The would-be astronauts were each outfitted with devices on their wrists that measured both their movement and the light they were exposed to. Using this data researchers were able to determine not only that the crew became less active over time, but that, even though the amount of sleep increased, the quality was poor, which wreaked havoc with their sleep cycle. "The majority of crew members also experienced one or more disturbances of sleep quality," the study explains.

"If you're not active, you can suffer loss of bone and muscle."

While this wasn't too problematic on the fake Mars mission, in space the lack of activity could lead to real physical problems. "In the microgravity found in space, which we didn't simulate, if you're not active, you can suffer loss of bone and muscle, and decondition your cardiovascular muscle very severely, making it difficult to complete missions," researcher David Dinges told Space.com. And the solution could be all in the lighting — researchers believe that tweaking the color and intensity of lighting, along with the timing, could positively impact the crew's circadian cycle and keep them more alert.