A Behavioral Circuit Breathing Training Intervention on Smoking Cessation and Respiratory Function Among Youth Who Use E-cigarettes

Inclusion Criteria: * Male or female, aged 15-25 years. * Regular e-cigarette use for at least 6 months and current e-cigarette use, defined as using e-cigarettes at least 1 day per week or at least 10 puffs per day during the past 30 days. * No regular exercise during the 6 months prior to the study, defined as exercising fewer than 2 times per week. * Willing and able to cooperate, with no communication difficulties, and able to follow the instructor's instructions. * No history of heart disease or respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD). * No hypertension, or controlled hypertension with resting blood pressure not exceeding a systolic blood pressure of 140 mmHg and a diastolic blood pressure of 90 mmHg (Whelton et al., 2018). * Able to move independently without assistance from another person or the use of assistive devices. * Voluntarily agrees to participate in the study and is willing to sign the informed consent form. * For participants younger than 18 years, consent must also be obtained from a legally authorized representative or parent/guardian. Exclusion Criteria: * An unforeseen circumstance prevents them from continuing participation in the study, such as an accidental injury or illness. * Unable to participate consistently in the breathing training program as required, defined as attending fewer than 80% of all scheduled training sessions. Participants must attend at least 15 sessions. * No longer willing to continue participating in the study. * Concurrent use of illegal drugs or other tobacco or nicotine products, such as conventional cigarettes, waterpipe tobacco (hookah), hand-rolled tobacco, e-cigarette liquids, or other nicotine-containing products.