The Effect of Water Temperature on Heart Rate Variability and Cognition

Effects of Water Temperature on Heart Rate Variability During Cognitive Testing in Healthy Adult Women: A Randomized Crossover Trial

Heart rate variability (HRV) is a key indicator of fitness, and stress resilience. Previous research has shown that HRV decreases under mental workload, including during tasks that require strict attention. Studies also show that temperature exposure affects attention: cold increases the stress response while warm water has a calming effect. Very few studies combine thermal exposure with cognitive testing, and no controlled trials have investigated whether water temperature modulates HRV responses specifically during cognitive demand.

Study Overview

• Status: Not yet recruiting
• Conditions: Mental Acuity
• Intervention / Treatment: Other: water

Detailed Description

Heart rate variability (HRV) is a widely recognized physiological marker that reflects the dynamic interaction between the cardiovascular and autonomic nervous systems. HRV represents millisecond-level fluctuations in time between consecutive heartbeats. It is a key indicator of autonomic nervous system balance, with higher values indicate better recovery, fitness, and stress resilience. Previous research has shown that HRV decreases under mental workload, including during tasks that require attention, inhibition, or executive function.1-3 Studies also show that temperature exposure affects autonomic regulation: cold increases sympathetic drive, while warm water supports parasympathetic activation.4-6 Very few studies combine thermal exposure with cognitive testing, and no controlled trials have investigated whether water temperature modulates HRV responses specifically during cognitive demand.

• Study Type: Interventional
• Enrollment (Estimated): 30
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Carol Johnston; Phone Number: 6024963463; Email: carol.johnston@asu.edu

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Healthy women free of chronic disease (by self-report)
• 18-30 years of age

Exclusion Criteria:

• medication/drug use that has not been consistent for the previous 3 months or will be discontinued during the trial
• any acute illness
• regular use of cigarettes or marijuana
• pregnant or lactating women
• not fluent in English
• not willing to attend two in-person lab visits in downtown Phoenix and follow study protocol (including abstaining from caffeine in the 12 hours prior to testing)
• not currently competing in sports or unusually high-intensity exercise protocols (e.g., high-intensity exercise greater than 30 minutes most days of the week)

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Warm water; Water will be heated to ~55º C (131 ºF)	Other: water; water temperature
Placebo Comparator: Cold water; Cold water: 4-6º C (41ºF)	Other: water; water temperature

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
heart rate variability	the measure of the variation in time between consecutive heartbeats	3 minutes
cognitive performance	Trail making test that measures cognitive flexibility, visual attention, and executive function, with interpretation based on completion times (in seconds)	3 minutes

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
cognitive performance	Stroop Color-Word Test which measures attention span, reaction time, and ability to resist distractions	3 minutes
cognitive performance	reaction time: measured by the elapsed time between stimulus onset and an individual's response	3 minutes

Collaborators and Investigators

• Sponsor: Arizona State University
• Investigators: Principal Investigator: Carol Johnston, Arizona State University

Study record dates

Study Major Dates

• Study Start (Estimated): July 13, 2026
• Primary Completion (Estimated): December 15, 2026
• Study Completion (Estimated): June 15, 2027

Study Registration Dates

• First Submitted: June 10, 2026
• First Submitted That Met QC Criteria: June 12, 2026
• First Posted (Actual): June 17, 2026

Study Record Updates

• Last Update Posted (Actual): June 17, 2026
• Last Update Submitted That Met QC Criteria: June 12, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: cognitive performance; heart rate variability; water temperature
• Additional Relevant MeSH Terms: Inorganic Chemicals; Anions; Ions; Electrolytes; Hydroxides; Alkalies; Oxides; Oxygen Compounds; Water
• Other Study ID Numbers: STUDY00024174

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No