The goal of this clinical trial is to examine the effect of a single 40-minute sauna session on glucose control in individuals at risk for metabolic impairments.

Research Questions:

• Can a single sauna session completed before a meal reduce the post-meal blood glucose response?
• Can a single sauna session improve 24-hour glucose control?

Study Design:

Participants will complete two lab visits: one involving a sauna session and one placebo visit (resting condition). Researchers will compare the effects on glucose control using a continuous glucose monitor (CGM).

What Participants Will Do:

Attend a sauna familiarization session Have a CGM sensor placed on the upper arm Visit the lab twice (once for sauna, once for placebo) Consume three standardized meals at home after each session

At least 72 hours prior to the first trial, participants will complete a familiarization session consisting of two 20-minute infrared sauna exposures. The study employs a randomized crossover design, with each participant completing both experimental conditions-infrared sauna (two 20-minute sessions at 175°F / 79°C, separated by a 5-minute break) and seated rest (two 20-minute periods of quiet sitting, separated by a 5-minute break)-separated by at least 72 hours. On each trial day, participants will arrive at the laboratory at 7:50 a.m. after an overnight fast from 8:00 p.m., with water permitted throughout. Participants will wear a continuous glucose monitor (CGM) during both trial days. Baseline measurements of blood pressure, heart rate, and oral body temperature will be recorded, and food logs reviewed. Following the condition session, a sedentary recovery period will occur until 9:45 a.m., with repeated physiological measurements. Final measurements of blood pressure, heart rate, and oral body temperature will be collected prior to a standardized breakfast provided from 9:45 to 10:10 a.m. Participants will depart thereafter by car or public transportation and remain sedentary for the remainder of the day. Meals for the rest of the day, i.e., breakfast, lunch, dinner, and a bedtime snack, will be provided and identical across trial days. Participants will fast again from 9:00 p.m. until 9:00 a.m. the following morning.

Inclusion Criteria:

Are 30-55 years old

Have a body mass index of ≥ 27 kg/m2

Have a waist size >102 cm (men) or >88 cm (women)

Have access to transportation for the 2 experimental visits (e.g., car, public transit, or drop-off).

Are cleared for participation based on the Physical Activity Readiness Questionnaire (PAR-Q+).

Exclusion Criteria:

Take medications that affect blood sugar

Exercise intensely 2+ times/week

Have diabetes, heart issues, low blood sugar or pressure

Are pregnant

Regularly use saunas or other heat therapy 1+ times/week