Submerging forearms in water may help protect older adults during extreme heat

UNIVERSITY PARK, Pa. — When air conditioning is not available during extreme heat, millions of older adults and other people become vulnerable to cardiac problems and other heat-related illnesses, according to researchers in the Penn State Department of Kinesiology. A new study by those researchers demonstrated that submerging hands and forearms in room-temperature tap water — around 68 degrees Fahrenheit — can be an effective, low- or no-cost method for cooling older adults and reducing their heart rate during extreme heat.  

The study was recently published in Experimental Physiology. 

“Older adults are more vulnerable to heat than younger people,” said Rachel Cottle, who earned her doctorate in kinesiology from Penn State earlier this year and was lead author of this study. “They do not sweat as efficiently as younger people, and they cannot pump blood to their skin as well, either. Because these important cooling mechanisms decline as we age, older people die much more frequently during extreme heat.”

The researchers tested hand and forearm immersion because it has previously been shown to be effective for mitigating heat stress in young adults in the military, but it had never been studied in older adults. Other similar interventions, like submerging feet in water or dousing oneself with water were found to be ineffective in previous studies.

The goal of this work, Cottle said, was to see if hand and forearm immersion could limit the rate at which temperature increases in the body’s core. Increasing core temperature increases heart rate and puts strain on the cardiovascular system. It can also lead, over time, to heat exhaustion and heat stroke, resulting in injury or death.

The researchers recruited 12 healthy adults over 65 years old. Participants were exposed to two hours of heat stress at 93 degrees Fahrenheit and 77% humidity, which is hot enough to cause older adults’ core temperatures to rise progressively over time, according to a previous study by the same team.

In half of the trials, participants were provided with a basin of approximately 68 degrees Fahrenheit water — the typical temperature for tap water — after one hour. They submerged their hands and arms up to their elbows in the water for 10 minutes. They then removed their hands and forearms from the water and repeated the process again 20 minutes later.

In other experiments, the same participants sat in the hot chamber with no cooling intervention. All participants completed the experiment four times — twice with forearm and hand immersion and twice without the intervention.

This experiment was designed to simulate a person filling their sink with tap water once and using that water repeatedly. During a power outage, people have no access to air conditioning or electric fans, but most people still have running water, the researchers said.

Results demonstrated that immersing one’s hands and forearms in tap water reduced both heart rate and the rise in core temperature.

“Core temperature was reduced by about half a degree Fahrenheit,” said Cottle, who is now a postdoctoral fellow at the University of Texas Southwestern Medical Center. “This may sound like a small amount, but it is enough to matter if someone is in danger of overheating. Of course, this will not keep someone safe indefinitely, but it could extend the amount of time before heat causes harm.”

Perhaps even more important, according to Cottle, was the reduction in heart rate. Because most heat-related deaths in older men and women are due to cardiac events, reducing the strain on the heart may keep people safer.

Despite the success of immersing hands in water, Larry Kenney, Cottle’s graduate adviser and senior author of this study, said that should not be people’s first strategy during a heat wave.  

“The first thing people should do is reduce the heat burden on their bodies, if at all possible,” said Kenney, professor of physiology and kinesiology and Marie Underhill Noll Chair in Human Performance at Penn State.  

Kenney said there are many simple steps people can take to cool themselves. 

“If possible, people should move to spaces with air conditioning — a friend’s house, a shopping mall, a library or a cooling center,” Kenney said. “People should be sure to stay hydrated, and — if air conditioning is not available, and they are not able to relocate — hand and forearm immersion is a good strategy. 

Electric fans can help cool people but have limitations, according to the researchers. During a power failure, electric fans do not work. Additionally, fans can help people lower their core temperature only in certain conditions. At very high temperatures, fans blow hot air that can actually increase core temperature. 

All these strategies are needed because extreme heat is becoming more frequent and severe, the researchers said. Additionally, due to increased demand for electricity to run air conditioners, heat waves frequently cause power failures. 

“One in eight people in the United States live without air conditioning,” Cottle said. “And, obviously, almost no one has air conditioning during a power outage. When we face extreme heat, if everyone takes precautions and looks out for older friends, family members and neighbors, we can protect many of the most vulnerable people among us.” 

Penn State kinesiology graduate students Kat Fisher and Olivia Leach; Lacy Alexander, professor of kinesiology at Penn State; and David Conroy, professor of applied exercise science at University of Michigan, also contributed to this research.