Behavior / Exercise

Hot Fun in the Summertime

Glorious summer time! All you have to do is visit any local bike trail or park to observe that your friends and neighbors are more likely to be out and about in the warm weather.  Longer daylight hours, ample sunshine, and access to more recreational facilities in the spring and summer all contribute to greater physical activity. But today I set out to quantify this opservation: how much more active are we in warm weather?
Most available evidence strongly supports that we are substantially more active in the spring and summer than the fall and winter. For example, one study of almost 3000 Michigan adults found that leisure time physical activity was about 15-20% higher in the spring and summer. Authors found something interesting about these patterns, though. Duration, intensity and frequency of the primary physical activity for an adult was not markedly different in the colder months during the warmer months, so this didn’t explain the difference in overall physical activity patterns. What did? Adults were more likely to engage in a SECOND routine physical activity in the spring and summer months, thereby increasing overall physical activity. For example, almost 55% of adults performed a second activity in the summer, whereas only 39% of adults engaged in a secondary activity in the winter. From experience, I can say this seems quite logical. I run all year round, but add in leisure-time activities such as walking, biking, swimming and hiking more frequently in the summer.

Another study looked at changes in Chicago-area weather over 3 years and their impact on physical activity in older adults with arthritis. Again, data supported dramatic seasonal reductions in physical activity. For example, in November, the month with the lowest physical activity, adults were 38% less active than in June (the month with the highest physical activity). In addition, factors such as rain and snow, cold weather and shorter daylight hours were all associated with reductions in physical activity. Authors estimated that heavy rain reduced average physical activity by about 12%.   Similarly, authors noted that “the 5.7 hour average decrease in daylight hours between January and June was associated with over 14% fewer daily activity counts, or almost 70 additional minutes of completely sedentary time.”

Graph taken from J Epidemiol Community Health. 2012 May;66(5):474-6. doi: 10.1136/jech.2010.128090. Epub 2011 Feb 15.A comprehensive study of walking patterns in over 1300 German older adults found similar results. The change in global radiation between winter and summer increased average physical activity (walking) by almost 20 minutes/day in study participants, whereas a 10 degree increase in temperature augmented daily walking by about 7 minutes. The change in daylight hours from a short day (9 hours daylight) to a long day (16 hours daylight) resulted in a 12-13 minute increase in average daily activity. By contrast, wind speed, precipitation, and humidity all decreased physical activity patterns, as seen in the graph at right.

So, there’s no doubt that summer time is a fun time, with substantial increases in physical activity. But some additional patterns and behaviors– the incorporation of extra activities, the change in daylight hours, the reduction in stormy weather– also contribute to our exercise behaviors across the year.

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