As global temperatures climb and heat waves become an increasingly frequent and severe threat, vulnerable populations, particularly older adults, face heightened risks of heat-related illnesses and cardiac complications. Researchers from Penn State University’s Department of Kinesiology have identified a simple yet effective cooling strategy that could help mitigate these dangers when air conditioning is unavailable. Their experimental study demonstrates that intermittent immersion of the hands and forearms in room-temperature tap water—approximately 68 degrees Fahrenheit—significantly reduces cardiovascular strain and core body temperature during extreme heat exposure in older adults.
Older individuals are disproportionately affected by heat stress due to physiological changes associated with aging. According to lead author Rachel Cottle, who recently completed her doctorate in kinesiology at Penn State, aging impairs the body’s natural cooling mechanisms. Sweating, a primary method for heat dissipation, becomes less efficient, and the cardiovascular system struggles to direct blood flow towards the skin to facilitate cooling. These deficits exacerbate the risk of dangerous increases in core body temperature, which can precipitate heat exhaustion, heat stroke, and cardiac events—the leading cause of heat-related mortality among seniors.
Previous investigations have proven the efficacy of hand and forearm immersion for heat mitigation in young, physically active populations, such as military personnel. However, this approach had not been rigorously tested in older adults, who physiologically respond differently to thermal stress. Other common cooling interventions, including submerging feet or sporadically applying water to the skin, have demonstrated limited effectiveness. The Penn State team aimed to fill this critical knowledge gap by conducting controlled experiments designed to simulate real-world conditions for elderly individuals during heat waves.
In this study, twelve healthy older adults, all above the age of 65, endured two-hour sessions of controlled heat stress within an environmental chamber set at 93 degrees Fahrenheit with 77 percent relative humidity. These conditions provoke a steady rise in core temperature in vulnerable populations, mirroring prolonged exposure to severe heat waves. Halfway through the exposure period, participants intermittently immersed their hands and forearms up to the elbows in cool tap water for ten minutes, repeated after an additional 20 minutes. In other trials, the same participants experienced continuous heat exposure with no cooling intervention, serving as their own controls.
The simplicity of this intervention is noteworthy. The experiment’s design mimicked a realistic scenario where an individual fills a basin with tap water, maintains access during a power outage or heat emergency, and repeatedly cools their upper limbs. Given that most residential settings retain running water even during electrical blackouts, this accessible approach circumvents the reliance on air conditioning or electric fans, both often unavailable or insufficient under extreme heat stress and infrastructure failure.
Results from the study were compelling: hand and forearm immersion lowered the rise in core body temperature by approximately half a degree Fahrenheit compared to no intervention conditions. While this reduction may appear modest numerically, such a decrement in core temperature can be physiologically meaningful, especially in preventing the threshold at which thermoregulatory failure and heat-related illness occur. More crucially, the researchers observed a significant reduction in heart rate during and following immersion, indicating alleviated cardiovascular strain. Since cardiovascular events are the predominant cause of heat-related fatalities in older adults, mitigating this burden has important clinical and public health implications.
Despite the promising findings, senior author Larry Kenney, professor of physiology and kinesiology at Penn State, emphasized that this cooling method should complement, rather than replace, primary heat management strategies. Ideally, individuals should first seek cooler environments equipped with air conditioning or access communal cooling centers. Maintaining adequate hydration and minimizing heat exposure remain foundational recommendations during heat waves. However, when such measures are impractical, hand and forearm immersion offers a low-cost, scalable alternative with demonstrable physiological benefits.
The researchers also highlighted the limitations of electric fans during heat crises. Fans require operational electricity and may exacerbate thermal strain in environments where air temperature exceeds body temperature by blowing hot air onto the skin. Thus, fans may paradoxically elevate core temperature under certain extreme conditions. This underscores the urgency for alternative cooling strategies that can function independently of electricity and adapt to the physiologic vulnerabilities of at-risk populations.
Heat waves are growing in frequency, duration, and intensity worldwide due to climate change, posing unprecedented challenges to public health infrastructure. Concurrently, increased energy demand during heat events strains power grids and contributes to outages, which amplify risks for older adults who lack air conditioning. As reported by the research team, roughly one in eight Americans live without air conditioning, and almost none retain cooling capabilities during power failures. Innovative, accessible interventions like intermittent limb immersion can provide critical margin of safety for these individuals.
The study also reflects a multidisciplinary research collaboration involving graduate students and faculty from Penn State as well as experts from the University of Michigan. Their collective work advances understanding of thermoregulation in aging populations and offers practical guidance to reduce morbidity and mortality during heat emergencies. These findings enrich the field of environmental physiology by demonstrating the real-world applicability of targeted cooling strategies tailored to older adults’ unique physiological needs.
Rachel Cottle, now a postdoctoral fellow at the University of Texas Southwestern Medical Center, underscored the broader significance of the research in public health preparedness. She pointed to the importance of community vigilance, urging people to support vulnerable neighbors, friends, and family during heat waves. As extreme weather events escalate globally, adapting cooling approaches and reinforcing social networks are vital components of heat resilience.
This study marks a pivotal step in expanding the toolkit for thermal strain mitigation among older adults, a demographic disproportionately affected by climate-driven health risks. By quantifying the physiological benefits of a straightforward, no-cost intervention, it paves the way for practical recommendations that can be widely implemented to save lives. Future research may explore optimizing immersion protocols, investigating long-term outcomes, and extending findings to other susceptible groups.
Adaptation to a warming world requires innovative, evidence-based strategies that transcend technological and economic barriers. The Penn State team’s findings highlight how physiological insights can translate into accessible solutions that promote health equity. Hand and forearm water immersion offers a promising, scientifically grounded approach to buffering older adults against the growing threat of extreme heat, especially in resource-limited scenarios.
Subject of Research: People
Article Title: Intermittent hand and forearm immersion in 20°C water attenuates thermal, cardiovascular, and perceptual strain in older adults during heat stress
News Publication Date: 7-Jul-2025
Web References:
- Penn State Department of Kinesiology: https://hhd.psu.edu/kines
- Experimental Physiology Article: https://physoc.onlinelibrary.wiley.com/doi/10.1113/EP092789
- Humans’ Core Temperature Response Study: https://www.psu.edu/news/research/story/humans-cant-endure-temperatures-and-humidities-high-previously-thought
- Heat Waves and Power Failures: https://pubs.acs.org/doi/10.1021/acs.est.1c00024
References:
Cottle, R., Kenney, W.L., Fisher, K., Leach, O., Alexander, L., Conroy, D. (2025). Intermittent hand and forearm immersion in 20°C water attenuates thermal, cardiovascular, and perceptual strain in older adults during heat stress. Experimental Physiology. DOI: 10.1113/EP092789
Keywords: Heat waves, Environmental stresses, Physiological stress, Heat, Older adults, Public health, Extreme weather events, Relative humidity, Weather
