The weather in your area may be a plus or a minus when it comes to exercise.

Sure, you can exercise year-round inside. And many people brave hot, cold, rainy, or snowy conditions to be active. But the weather can still make a difference, new research shows.

The CDC advises getting at least half an hour of moderate intensity physical activity five or more days per week. According to the CDC, moderate-intensity physical activity includes walking at a brisk pace, biking on a level terrain, using a stationary bicycle, aerobic dancing, or water aerobics.

Ray Merrill, PhD, MPH, and colleagues aren't offering new excuses to slack on fitness. Instead, they looked at the weather's effects on workout habits.

Merrill is an associate health sciences professor at Brigham Young University. His report appears in the American Journal of Health Behavior.

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Prime Exercise Conditions

Looking for the best weather for exercise? Head to "big sky" country.

Here are the ten top-ranked areas, with the percentage of people meeting moderate physical activity guidelines:

—Montana: 60.9 percent

—Utah: 59.2 percent

—Wisconsin: 57.9 percent

—New Hampshire: 55.9 percent

—Vermont: 55.6 percent

—Maine: 55.1 percent

—Idaho: 54.8 percent

—Washington: 53.9 percent

—Nevada: 53.8 percent

—Wyoming: 53.4 percent

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The five with the lowest percentages were:

—Puerto Rico: 30.9 percent

—Hawaii: 36.4 percent

—North Carolina: 37.4 percent

—Kentucky: 37.6 percent

—Mississippi: 38.4 percent

Montanans are most likely to meet physical activity recommendations, says Merrill. People living in Puerto Rico are the least likely to do so, he writes.

You don't need radar to tell the difference between those climates.

The highest-ranked regions for physical activity also had the most dry, moderate days. Those at the bottom 25 percent of the list had the highest percentage of sticky, steamy, tropical days.

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Seasonal Shifts

The time of year also affected activity. Activity peaked with:

—Moist, moderate winters

—Dry "polar" springs

—Dry, tropical summers

—Dry "polar" falls

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Why the Difference?

The researchers suggest three reasons for the patterns:

—Some active people may consider climate in choosing where to live.

—Some older people may not feel comfortable in gyms. They may wait for good weather to be active.

—Good weather is often considered safer and more pleasant.

—Walking and cycling, two popular activities, are more convenient in good weather.

Data SourcesPhysical activity data came from a 2003 phone survey done by the CDC and U.S. states or territories.

A total of 355 counties were involved. Surveys included adults aged 18 and older living in the community.

Weather information came from 255 weather stations.

Results were not listed for Alaska.

Before starting any exercise program, speak with your doctor. Together you can find an activity that is safe for you and one that fits your needs.

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By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Merrill, R. American Journal of Health Behavior, July/August 2005; vol 29: pp 371-381. CDC: "Physical Activity: Recommendations." Health Behavior News Service.