It's that time of year again -- the fitness centers on campus are suddenly crowded. But why are they more crowded now than ever before?

"In the beginning of the semester, no matter what, there's always that big rush where everyone thinks they'll get in shape for their New Year's resolutions or what not. But it always dies down once school gets started," said Brian King (freshman-division of undergraduate studies), who works at the White Building.

"People come here more for cardio in the winter because they can't run outside," he added.

Norman Jones (senior-psychology) has worked at the White Building for about two years and has seen the trends. "I think that it's typically crowded in the beginning of both semesters," he said. "The lines to get into the gym die down because people give up or get busy. They usually start coming to get in shape for spring break this time of year."

Chip Harrison, head strength and conditioning coach, agrees that the number of people who come to the fitness centers is higher in the winter.

"It is the busiest time of year in the industry across the country," Harrison said. "People come to fulfill their New Year's resolutions to increase their fitness and appearance. People also prefer indoor venues when it is the middle of January to avoid the weather."

According to Harrison, however, participation in classes does decrease over the spring semester.

"People are more active outside in the spring because it is starting to warm up," he said. "In the beginning, when the classes are crowded, there is a lot of competition for space, so as the semester goes on, people find other ways to work out."

But why is it that people generally become less active in the fall and winter? Why do people oversleep and overeat?

While it may not seem obvious, there are several reasons why people work out less in late fall and early winter than other times of the year. According to Dr. Frederick Brown, associate professor of psychology and director of the Psychobiological Rhythms Laboratory, light plays an essential role in controlling human alertness and activity. This sensitivity to light can be explained through common mood disorders.

According to the Seasonal Pattern Specifier, seasonal mood disorders are defined by temporal relationships with the onset of depression, with full remission or wellness returning in spring and summer months. Seasonal Affective Disorders are defined by the onset of depression two years in a row.

"It can be helped by artificial illumination, particularly early in the morning," Brown said. "Seasonal episodes are characterized by prominent lack of energy, oversleeping, overeating, pseudo-hibernation and having trouble waking up in the morning."

Apparently, there is a genetic disposition in temperate and higher latitudes as well as in age and sex, he added.

"Seasonal episodes occur much more in higher latitudes. Age and gender are also strong predictors. Women comprise 60 to 90 percent of the population with seasonal mood disorders," said Brown. "Personally, I think women are more sensitive to light changes. My research demonstrated the full moon synchronization effect. Along with it, gynecologists have correlated the onset of menstrual bleeding with the full moon."

Brown's research suggests that sensitivity to light has much to do with how our bodies function. Light controls a majority of what makes us alert and sleepy.

"Light suppresses melatonin, a hormone produced by the pineal gland that puts us to sleep," said Brown. This explains why people are more awake in bright light than in dim light and why people tend to fall asleep in darkness.

"When spring comes, people's moods tend to lift because the sun's energy is stronger and brighter, so people tend to get up earlier when they are exposed to the sunlight," Brown said.

The warmer weather also tends to make people more active.

"In places like the desert, although at the same latitudes as many North American areas, people aren't suffering so much from Seasonal Affective Disorder," Brown said. "Glare from sand and snow tend to make the environment brighter and keep people more alert and active." Hence, the peak of depression from seasonal affective disorder usually comes before snow, in late fall when the leaves come down.

Temperature is less of a factor in controlling sleep and energy levels than light.

"Our eyes take in the light for daily rhythms. The longer the light stays, the longer we are stimulated ... within limits," said Brown.

This accounts for our circadian rhythm, whereas our homeostatic system accounts for our energy lost and will remind us to sleep.