Optimal Frequency of High-Intensity Interval Training for Centrally Obese Adults

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)