# Alternating high-intensity interval training and continuous training is efficacious in improving cardiometabolic health in obese middle-aged men PMID: 34987589 Journal: Journal of Science and Medicine in Sport Published: 2022-04 Authors: Poon ET, Siu PM, Wongpipit W, Gibala M, Wong SH ## Question Do HIIT alone, MICT alone, or alternating HIIT-MICT produce different cardiometabolic, body-composition, fitness, enjoyment, self-efficacy, and adherence responses in inactive obese middle-aged men? ## Summary This randomized trial compared HIIT, MICT, alternating HIIT/MICT, and no exercise for 16 weeks in inactive obese middle-aged Asian men. All exercise groups improved VO2max by about 15% and reduced weight, BMI, body fat percentage, and waist circumference compared with control. HIIT, MICT, and alternating HIIT/MICT had similar enjoyment, self-efficacy, and adherence above 80%, with one minor knee-pain incident in the HIIT group that resolved after brief rest. ## Population - Inactive obese Asian middle-aged men. - Sample size: 42 - Age: Mean 42 +/- 5 years; recruited ages 40-59 years. - Sex: Male - Fitness level: Inactive, baseline VO2max about mid-30s mL/kg/min. - Health status: Obese by Asian BMI criterion, without severe uncontrolled medical contraindications. ## Methodology - Four-arm randomized controlled trial with three exercise arms and a non-exercise control group. - 16 weeks - First two sessions supervised in a laboratory, then mostly unsupervised free-living treadmill or outdoor running/walking with HR monitoring. - Randomized and controlled study design. ## Protocol - HIIT. - Modality: Running, jogging, or brisk walking on treadmill or outdoors. - Work intervals: 1 minute. - Recovery: 1 minute walking at 50% HRmax. - Sets or repetitions: 12 bouts at full protocol. - Intensity: 80-90% HRmax during work bouts. - Session duration: About 29 minutes at full protocol including 3-minute warm-up and cool-down. - Frequency: 3 days/week. - Program length: 16 weeks. - Progression: 50% protocol duration weeks 1-2, 75% weeks 3-4, full protocol afterward. - MICT, alternating HIIT-MICT, control. - Modality: Brisk walking/running or no exercise. - Work intervals: MICT continuous 40 minutes at 65-70% HRmax; alternating group switched HIIT and MICT by session. - Sets or repetitions: One continuous MICT bout or alternating protocol by session. - Intensity: MICT 65-70% HRmax; control no exercise. - Session duration: MICT about 46 minutes at full duration including warm-up/cool-down. - Frequency: 3 days/week for exercise groups. - Program length: 16 weeks. - Progression: Same 50%, 75%, then full duration progression for exercise protocols. ## Outcomes ### VO2max Status: improved All exercise groups improved VO2max by about 15% compared with baseline and control. HIIT 34.3 to 39.1; MICT 34.9 to 39.4; HIIT-MICT 34.4 to 40.3 mL/kg/min; ANCOVA p=0.009. ### Body composition Status: improved All exercise groups reduced weight, BMI, body fat percentage, and waist circumference compared with control. Between-group effects for weight/BMI/fat/waist p<0.05, partial eta squared 0.06-0.09. ### Blood markers Status: mixed No significant post-intervention group differences for blood markers; HIIT-MICT improved cholesterol/LDL from baseline and HIIT improved fasting insulin/HOMA-IR from baseline. ANCOVA for all blood markers p>0.05; within-group total cholesterol and LDL decreased after HIIT-MICT; fasting insulin and HOMA-IR improved after HIIT. ### Adherence, enjoyment, safety Status: mixed Adherence exceeded 80% and enjoyment/self-efficacy did not differ; one minor knee pain episode occurred in HIIT. Enjoyment p=0.789, self-efficacy p=0.345, adherence p=0.576. ## Practical Insights - Alternating HIIT and MICT can be presented as an evidence-backed option for users who want variety without sacrificing likely fitness/body-composition benefits. - For inactive users, ramping from half volume to full volume over four weeks is a practical progression pattern. - When calorie expenditure is matched, HIIT may save time but should not be marketed as clearly superior for fat loss. ## Limitations - Small sample size. - Male-only, middle-aged Asian sample. - No direct insulin sensitivity measure such as clamp or OGTT. - Mostly free-living training may create uncontrolled variation. ## Safety And Adherence - One minor knee-pain incident occurred in the HIIT group and resolved after a few days of rest. - No other training-related adverse events were reported. - Severe hypertension and unstable cardiovascular disease were excluded. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/34987589/) (pubmed) - [DOI](https://doi.org/10.1016/j.jsams.2021.11.010) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8689221/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.