The air is heavy, you break a sweat in mere seconds and your lungs feel like they’re going to explode. If you’re a runner, you know that hot, humid days are the worst. It’s harder to get that workout high and easier to say, “Well, maybe tomorrow.”

But secretly, didn’t you always wonder if maybe it was just you? If everybody else is out there pumping and you’re the only one who chose air conditioning instead of body conditioning?

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A researcher at Brigham Young University recently examined the effect of weather on workouts and the results of Ray Merrill’s study might surprise you. Residents of Montana, Wisconsin and New Hampshire are much more likely to get enough physical activity than those of Florida, Hawaii, California or Puerto Rico.

The results surprised Merrill and his colleagues. They were struck by how strong the relationship was between low levels of physical activity and the weather in some tropical areas.

And let’s face it, don’t we all know somebody who has moved South to get away from cold Northern weather. They’ll work out more, they say, play more golf, do more running. It’s just not happening.

Merrill and his colleagues matched data from 255 weather stations with results from a physical activity survey of people in 355 U.S. counties. The results were published in the July/August 2005 issue of American Journal of Health Behavior.

After Montana, with 60.9 percent of respondents meeting recommended physical activity levels, the states with highest percentages were Utah with 59.2 percent, Wisconsin with 57.9 percent and New Hampshire with 55.9 percent.

“It’s pretty obvious that weather influences physical activity,” Merrill says. “It’s intuitive that cooler, milder weather days are associated with more activity — but it’s never really been quantified before.”

After Puerto Rico, at 30.9 percent, the states with the lowest percentages were Hawaii with 36.4 percent, North Carolina with 37.4 percent and Kentucky with 37.6 percent.

Physical activity also varied significantly among seasons, with activity highest in summer at 48.4 percent, 46.2 percent in spring, 45.8 percent in fall, and 44.6 percent in winter.

Weather measurements — taken four times a day at each weather station — included daily air temperature, dew point temperature, wind speed direction, sea level pressure and total cloud cover.

To gauge physical activity, the researchers took data from an ongoing national telephone survey of adults age 18 and older, a project between Centers for Disease Control and Prevention and U.S. states and territories.

The research team found that highest physical activity was linked to moist moderate conditions in winter, dry polar in spring, dry tropical in summer and moist polar in fall.

Moist tropical air is warm and very humid, with cloud cover in winter and partial cloud cover in summer. Muggy conditions were consistently associated with the lowest percentages of recommended physical activity, the researchers say.

Dry tropical air is warm and sunny. Polar air, which leads to coldest conditions, can be either dry with little cloud cover or moist with cloud cover and, often, precipitation.

The areas in the top 25 percent for physical activity had the highest percentage of dry, moderate days, followed by moist polar days, then dry polar. Areas in the bottom 25 percent had the most days in moist tropical conditions.

Researchers said that the data could have been slightly skewed by physically active people who move to an area specifically for its climate, for instance, skiers who seek moist, moderate winter conditions.

Recommended exercise was defined as 30 minutes of moderate physical activity five to seven days a week or 20 minutes of vigorous physical activity three to seven days a week. Moderate activity included brisk walking, biking, vacuuming, and gardening; vigorous activity included running, aerobics and heavy yard work.

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