It is well-accepted that an exaggerated blood pressure (BP) response to physical stress has a prognostic value, indicating a higher cardiovascular risk (e.g., sudden cardiac death, myocardial infarction, future hypertension, and left ventricular hypertrophy). However, there is a limited understanding of the underlying mechanisms and therapuetic strategies modulating this response. Therefore, this pilot project aims to explore whether one session of low-volume high-intensity interval training (low-volume HIIT) or combined intermittent heat and cold bath (sauna+cold bath) can decrease BP responses to physical stress. Furthermore, the secondary goal is to investigate whether one brief session learning about positive stress expectations magnifies the decrease in BP following low-volume HIIT and sauna+ cold bath.

Inclusion Criteria:

• Male or female between 18 to 50 years
• Non-smoker.
• Non-obese (<30 kg/m2).
• Able to walk on a treadmill and cycle on a stationary bike without problems.
• No or little (frequency < 2 times per month) experience swimming with sauna and cold water.
• Proficient in Norwegian and able to provide informed consent.

Exclusion Criteria:

• Current or previous regular smoker
• Addictions to alcohol or illegal drugs
• Diagnosed with cardiovascular, respiratory, metabolic, or autoimmune diseases
• Taking prescription medication with known cardiovascular effects
• Judgment by a medical provider that exercise, heat therapy, or hydrotherapy poses an undue burden or risk.
• Cognitive or psychiatric impairment
• Lack of proficiency in Norwegian language oral or writing skills that will hamper the ability to participate in the interventions and fill out questionnaires.