By Pat Anson, Editor

The debate over weather’s influence on pain is heating up again, with the release of a new study that showed warmer temperatures -- not rainy conditions -- are associated with an increase in online searches about joint pain.

The apparent increase in knee and hip pain may be due to increased outdoor physical activity, according to researchers who reported their findings in PLOS ONE.

Investigators used Google Trends to analyze how often people used Google’s search engine to look up words and phrases associated with hip pain, knee pain and arthritis. Then they compared the results with local weather conditions at 45 U.S. cities. The weather data included temperature, precipitation, relative humidity and barometric pressure - conditions previously associated with increases in musculoskeletal pain.

Researchers found that as temperatures rose, Google searches about knee and hip pain rose steadily, too. But knee-pain searches peaked at 73 degrees Fahrenheit and became less frequent at higher temperatures. And searches for hip-pain peaked at 83 degrees and then tailed off.

Surprisingly, rain actually dampened search volumes for both knee and hip pain.

"We were surprised by how consistent the results were throughout the range of temperatures in cities across the country," said Scott Telfer, a researcher in orthopedics and sports medicine at the University of Washington School of Medicine.

Searches about arthritis, which was the study's main impetus, had no correlation with weather conditions.

"You hear people with arthritis say they can tell when the weather is changing," he said. "But with past studies there's only been vague associations, nothing very concrete, and our findings align with those."

What do the findings mean?

Because knee and hip-pain searches increased until it grew warm, and rainy days tended to slightly reduce searches for hip and knee pain, the researchers speculate that changes in outdoor physical activity may be primarily responsible for those searches.

"What we think is much more likely explanation is the fact that people are more active on nice days, so more prone to have overuse and acute injuries from that and to search online for relevant information,” Telfer said, adding that web searches are often the first response people have to health symptoms.

Researchers in Australia recently reported that cold, rainy weather has no impact on symptoms associated with back pain or osteoarthritis. Warmer temperatures did slightly increase the chances of lower back pain, but the amount of the increase was not considered clinically important. 

A previous study on back pain and weather by The George Institute for Global Health had similar findings, but received widespread criticism from the public, a sign of just how certain many people are that weather affects how much pain they feel.

“I know it is going to rain or have a thunderstorm before the weather person announces it on the news,” says Denee Hand, who suffers back pain from arachnoiditis, a chronic inflammation of the spinal membrane. She says the pain spreads down to her toes when the weather changes. 

“It is like my nervous system and muscles react to the coming weather and finally I get pain that feels like the tops of both my feet are being crushed,” she said in an email to PNN. “I have compression of the spinal cord with nerve damage to my nerves from the scar tissue and when the weather changes the scar tissue presses down against the damaged nerves.”

Researchers at the University of Manchester recently ended a study involving thousands of people who used smartphone apps to report their pain levels, giving investigators the ability to compare the pain data with real-time local weather. Researchers are now analyzing the database compiled over the last 15 months and will release their results next spring.