The aim of this study is to examine the therapeutic effectiveness of two different exercise frequencies of high-intensity interval training (HIIT; once versus thrice weekly, with matched weekly exercise volume) on improving cardiometabolic risk factors in centrally obese adults.

HIIT is an emerging, popular, promising, cost-effective, and time-efficient exercise modality for managing obesity. Although lower-frequency HIIT is favorable for intervention adherence, the optimal exercise frequency of HIIT for alleviating obesity is unknown.

This study is a three-arm randomized controlled trial. Centrally obese adults will be randomly allocated to three groups: the usual care control, once and thrice-weekly HIIT groups. Led by research personnel, the usual care group will receive obesity-related health education. Led by athletic coaches, the HIIT intervention groups will receive 16 weeks of once or thrice weekly HIIT (with matched weekly exercise volume). Outcome measures of this study will be examined at baseline, 4 months (post-intervention), and 8 months (follow-up), by assessors blinded to group allocation.

Inclusion Criteria:

• Aged above 18 years
• Ethnic Chinese
• Overweight (BMI ≥23 for Asian)
• Centrally obese according to IDF and NCEP with Asian-specific cut-off (waist circumference ≥90 cm for males; ≥80 cm for females)
• Males and females

Exclusion Criteria:

• Medical and somatic conditions that prevent brisk walking
• Chronic diseases affecting mobility and motor function (e.g., neurological disease, musculoskeletal disorder, spinal cord injury, autoimmune, arthritis, Parkinson's Disease)
• Chronic diseases affecting cardiorespiratory and metabolic health (e.g., cancers, cardio-/cerebrovascular diseases, heart disease, diabetes mellitus, pneumonia, chronic pulmonary diseases, nephritis, nephrosis)
• Signs of cardiac arrhythmia indicated by aberrant electrocardiography during incremental VO2max test
• Regular moderate-to-vigorous intensity exercise (≥150 min weekly) in the past 3 months, as screened by a specially designed questionnaire
• Daily smoking habit
• Excess alcohol consumption (daily ≥30g for men, ≥20g for women) in the past six months
• Claustrophobia
• Surgery, therapy or medication for obesity or weight loss in the past six months (e.g., gastric bypass, gastric band, sleeve gastrectomy, gastric reduction duodenal switch, and dietitian-prescribed dietary program)

The data of individual participants that underlie the results reported in this trial, after de-identification including text, tables, figures, and appendices, as well as study protocol and statistical analysis plan, will be shared after 3 months of study publication. Data will be shared with researchers who provide a methodologically sound proposal for academic purposes. Proposals should be directed to pmsiu@hku.hk to gain access and for data request, a data-access agreement needs to be signed.

Beginning 3 months and ending 3 years following the publication of the article.

Data will be shared with researchers who provide a methodologically sound proposal for academic purposes. Proposals should be directed to pmsiu@hku.hk to gain access and for data request, a data-access agreement needs to be signed.