Background: The relationship between the frequency of high-intensity interval training (HIIT) and the resultant adaptations is largely unclear. Purpose: This study examined the effects of different frequencies of HIIT compared to moderate-intensity continuous training (MICT) on body composition and cardiovascular biomarkers in overweight or obese adults. Methods: This study was a randomized, controlled, single-blinded trial. Fifty-six overweight or obese men aged between 18 and 30 years were randomly assigned to no-intervention control (CON; n=14), MICT performed thrice weekly (MICT×3/wk; n=9), HIIT performed thrice weekly (HIIT×3/wk; n=14), HIIT performed twice weekly (HIIT×2/wk; n=10), and HIIT performed once weekly (HIIT×1/wk; n=9). Each HIIT session consisted of 12 × 1-min bouts at 90% heart rate reserve (HRR), interspersed with 11 × 1-min bouts at 70% HRR (HIIT×3/wk: 69 min/wk; HIIT×2/wk: 46 min/wk; HIIT×1/wk: 23 min/wk). Aerobic capacity, resting heart rate, body composition, waist circumference, blood pressure, endothelial function, fasting blood glucose and lipids, circulatory adipokines and inflammatory biomarkers were examined at baseline, after 4 weeks and 8 weeks of intervention.

Individuals who fulfilled the following inclusion criteria were invited to participate in the present study: 1) Chinese male; 2) aged 18-30 years; and 3) overweight or obesity, defined as BMI ≥23 kg/m2 (classification of overweight for Hong Kong adults according to Department of Health, Hong Kong SAR Government) (13). Subjects were excluded if they had: 1) chronic medical and health condition such as cardiovascular diseases, diabetes, neurological disease, musculoskeletal disorder, cancers, and autoimmune diseases; 2) hypertension (blood pressure >140/90 mmHg); 3) contraindications to participating in physical exercise; 4) any pre-existing medical or physical issues that affected the experimental test; 5) physically active (i.e., >3 hours of moderate-intensity exercise weekly) or 6) lean overweight population (BMI ≥23 kg/m2, but percent body fat ≤20%) according to the BMI data corresponding to bioelectrical impedance estimated percent body fat cut-off value among Hong Kong Chinese adults.

Of those who were screened, 103 Chinese young adults were eligible to participate in this study. They were provided with written and verbal information on the study protocol and the possible associated discomforts and risks followed by obtaining their written informed consent to participate in this study. The study protocol and consent form were approved by the Human Subjects Ethics Sub-Committee of The Hong Kong Polytechnic University (ethics approval reference number: HSEARS20160927005-01).

This study was a single-blind, randomized, controlled trial. Subjects were randomly assigned to 1) no-intervention control (CON), 2) MICT performed thrice weekly (MICTx3/wk), 3) HIIT performed thrice weekly (HIITx3/wk), 4) twice weekly (HIITx2/wk), and 5) once weekly (HIITx1/wk). All subjects were instructed to maintain their usual daily activities. Outcome measures including aerobic capacity, body composition, blood pressure, resting heart rate, endothelial function, arterial stiffness, fasting glucose, lipids markers, adipokine marker, and inflammatory marker were assessed at baseline, 4 weeks and 8 weeks after the intervention.

Inclusion Criteria:

1. Chinese male
2. Aged 18-30 years
3. Overweight or obesity, defined as BMI ≥23 kg/m2 (classification of overweight for Hong Kong adults according to Department of Health, Hong Kong SAR Government)

Exclusion Criteria:

1. Chronic medical and health condition such as cardiovascular diseases, diabetes, neurological disease, musculoskeletal disorder, cancers, and autoimmune diseases
2. Hypertension (blood pressure >140/90 mmHg)
3. Contraindications to participating in physical exercise
4. Any pre-existing medical or physical issues that affected the experimental test
5. Physically active (i.e., >3 hours of moderate-intensity exercise weekly)
6. Lean overweight population (BMI ≥23 kg/m2, but percent body fat ≤20%) according to the BMI data corresponding to bioelectrical impedance estimated percent body fat cut-off value among Hong Kong Chinese adults.