Tammy Walter tried exercising in the morning but quickly decided it wasn't for her.

"My body doesn't respond well to getting up in the morning," said the 42-year-old mother, who teaches a weekly early evening spinning class at the downtown YMCA. "I get a better workout in the evening. I burn more calories. In the morning ... I just wasn't awake."

Gary Bredehoft, however, starts his day exercising at 5 a.m. The owner of Tiger Training and co-director of the Lincoln Marathon said if he waited to work out later in the day, there would be the chance of things popping up to prevent it.

"I like getting up early," he said. "I feel I have more energy. It helps me mentally. I get that runner's high and get a mental boost from it. I feel good about the workout, knowing that I did it."

So is it better to exercise early or late?

There's no definitive answer, according to Shinya Takashi, a health and nutrition sciences professor at the University of Nebraska-Lincoln.

"It's all about preference and lifestyle," he said.

The most important thing is not when you exercise but how much you get out of it when you do and sticking to a routine.

"The bottom line is to have more calories going out than coming in," he said.

The trick is figuring out if you're an early bird or a night owl. Your body clock can help you determine that.

Human sleep and wake cycles follow a daily cycle called circadian rhythms. This cycle regulates our body temperature, blood pressure, alertness and metabolism, among other physiological functions.

Circadian rhythms are different for everybody. Walter discovered, through trial and error, that her optimal exercise time was in the evening.

"It's a nice break for me after work," she said. "All the stress, I just work it out, and I'm in a much better mood when I get home. It relaxes me, too."

Bredehoft encourages his clients to work out in the mornings because he knows people get busy during the day and may not have the time or energy to follow through on an evening workout. Still, he understands mornings are not ideal for everyone.

"You have to do what works for you," he said.

Here's a rundown of pros and cons for morning and evening exercises, according to a variety of websites specializing in exercise:

Morning exercise pros

* Exercising in the morning can leave you feeling more alert and invigorated.

* Morning exercise can increase your metabolic rate, allowing you to burn more calories throughout the day.

* Fewer distractions or disruptions can make it easier to commit to a morning schedule.

Morning exercise cons

* You begin working out with cold, stiff muscles.

* You may not be at peak energy or have as much endurance.

* Night owls may have trouble committing to a morning routine.

Evening exercise pros

* You can dedicate yourself more fully without worrying about being late for work.

* If you exercise after dinner, you may regulate how much you eat.

* Performance may be better because muscles are warm and flexible.

* Access to gym equipment often is better later in the evenings.

Evening exercise cons

* You may forgo a workout because you feel mentally or physically fatigued.

* Daily disruptions and distractions may force you to skip a workout.

* You may have trouble falling asleep if you exercise too late.

* Exercising outside at night can be dangerous, especially in the winter on icy, snowy sidewalks and bike paths.