This study aims to investigate the differences in cardiovascular stress response patterns among individuals with various physical activity levels (sedentary controls and different types of athletes). By synchronously monitoring ECG, heart rate, skin sympathetic nerve activity (SKNA), blood pressure, and cardiac output, the study will characterize physiological dynamics during resting, orthostatic challenge, cold pressor stress, and maximal exercise.

Participants will be categorized into five groups based on their training background: sedentary, endurance, strength, technical, and traditional ethnic sports. The experimental protocol includes baseline measurements in lying, standing, and sitting positions, followed by a series of acute stress tests: a lie-to-stand orthostatic test, a slow breathing test, and a cold pressor test. Finally, participants will perform a ramp incremental exercise test on a cycle ergometer. Synchronous physiological data including HRV and SKNA will be collected to evaluate the dynamic regulation of the autonomic nervous system.

Inclusion Criteria:

Healthy young adults aged 18-25 years

Body Mass Index (BMI) within the range of 18.5-23.9 kg/m 2

No history of systematic professional athletic training (for sedentary group) or confirmed training background (for athlete groups)

No exercise contraindications or history of cardiovascular, respiratory, or metabolic diseases

No family history of sudden cardiac death

Ability to understand the study protocol and sign the informed consent form

Exclusion Criteria:

History of limb sports injury within the past 6 months or unhealed fractures

Habits of smoking or chronic alcohol consumption

Presence of implanted electronic devices (e.g., pacemakers)

Clinical diagnosis of psychiatric disorders such as anxiety or depression

Recent use of medications affecting autonomic or cardiovascular function

Regular practice of meditation or ongoing psychotherapy

Irregular menstrual cycles (for female participants)

Peripheral neuropathy or other autonomic nervous system disorders

The study population consists of 60-80 healthy adult volunteers (college students). Participants are categorized into five distinct groups based on their habitual physical activity levels and training backgrounds: 1) Sedentary controls, 2) Endurance athletes, 3) Strength athletes, 4) Technical athletes, and 5) Traditional ethnic sports practitioners (e.g., Tai Chi). Gender balance is maintained across all groups.