# Effects of different HIIT protocols on exercise performance, metabolic adaptation, and fat loss in middle-aged and older adults with overweight PMID: 39006847 Journal: International journal of medical sciences Published: 2024-06-24 Authors: Lee MC, Chung YC, Thenaka PC, Wang YW, Lin YL, Kan NW ## Question Which of two equal-duration cycling HIIT prescriptions, long intervals or medium intervals, is more effective for reducing fat accumulation and inflammation and improving metabolic adaptation and exercise performance in sedentary middle-aged and older adults with overweight? ## Summary This controlled full-text study compared two cycling HIIT formats in sedentary middle-aged adults with overweight: 4 x 4-minute intervals versus 8 x 2-minute intervals, both using equal 1:1 work-recovery structure, equal 32-minute interval-session duration, and 3 sessions per week for 8 weeks. Both HIIT formats improved VO2peak, but neither significantly improved body composition, glucose, blood lipids, or inflammatory markers. The longer-interval format produced a larger acute heart-rate response, post-exercise blood pressure reductions, and a signal for anaerobic power and adiponectin. ## Population - Sedentary adults aged 45-65 years with BMI 24-35 kg/m2; exclusion criteria removed smoking, alcohol use, diabetes, major cardiopulmonary, neuromuscular, metabolic, arrhythmic, vascular, thrombotic, orthopedic/surgical, neurologic, and medication-related risks. - Sample size: 36 - Age: L-HIIT 48.42 +/- 15.48 years; M-HIIT 46.33 +/- 12.40 years; control 47.58 +/- 15.44 years; eligibility stated age 45-65 years - Sex: L-HIIT 1 male/11 female; M-HIIT 3 male/9 female; control 3 male/9 female - Fitness level: Sedentary - Health status: Overweight; BMI approximately 25.88-26.92 kg/m2 by group mean ## Methodology - Controlled counterbalanced exercise intervention with three groups: long-interval HIIT, medium-interval HIIT, and no-exercise control; included 8 weeks of training plus 4 weeks of detraining follow-up. - 8-week training stage followed by 4-week detraining stage - Supervised exercise testing and training with certified athletic trainers; stationary spin-bike protocol - Controlled study design. ## Protocol - L-HIIT and M-HIIT cycling protocols. - Modality: Stationary spin bike. - Work intervals: L-HIIT: 4 min; M-HIIT: 2 min. - Recovery: L-HIIT: 4 min; M-HIIT: 2 min. - Sets or repetitions: L-HIIT: 4 repetitions; M-HIIT: 8 repetitions. - Intensity: Exercise 85-90% VO2peak; recovery 65-70% VO2peak. - Session duration: 32 min interval block plus 5 min warmup. - Frequency: 3 sessions/week. - Program length: 8 weeks, followed by 4-week detraining observation. - Progression: Fixed protocols; no progression described. - No-exercise control. - Program length: 8-week control period plus 4-week follow-up measurement. ## Outcomes ### VO2peak Status: improved Both L-HIIT and M-HIIT significantly increased VO2peak after 8 weeks; change rates were +27.93 +/- 16.79% for L-HIIT and +18.39 +/- 8.12% for M-HIIT compared with control, then declined after detraining. L-HIIT p<0.001, ES=0.785; M-HIIT p<0.001, ES=0.718; change-rate comparisons versus control p<0.001 and p=0.002 respectively. ### Body composition Status: no clear change Weight, body fat percentage, subcutaneous fat thickness, waist circumference, and hip circumference did not significantly change within or between groups, despite small nonsignificant downward trends in the HIIT groups. No significant differences reported at week 0, 8, or 12 or in change rates. ### Metabolic markers Status: no clear change Fasting glucose, total cholesterol, triglycerides, LDL, HDL, resting SBP, and resting DBP showed no significant group changes during the training or detraining stages. No significant within- or between-group differences in Table 6. ### Acute physiological response Status: mixed During a single week-4 HIIT session, L-HIIT produced a greater HR increase than M-HIIT and significant post-exercise reductions in SBP and DBP; both groups increased RPE and lactate. Delta HR +49.66 +/- 16.09% vs +33.22 +/- 14.37%, p=0.020; L-HIIT post-exercise SBP p=0.016 and DBP p=0.006 versus pre. ### Adiponectin Status: mixed Adiponectin was not significantly different between groups immediately after 8 weeks, but after 4 weeks detraining the L-HIIT group remained 1.78-fold higher than control. Week-12 L-HIIT vs control p=0.033, ES=0.157. ## Practical Insights - For overweight middle-aged adults, both 4-minute and 2-minute cycling intervals at 85-90% VO2peak, performed 3 times weekly for 8 weeks, can improve aerobic fitness. - Equal total hard-work time does not guarantee equal acute cardiovascular response; longer 4-minute intervals produced a larger HR response and acute post-exercise hypotension signal. - This protocol should not be used as evidence that 8 weeks of HIIT reliably reduces body fat or improves lipids/glucose in this population. - Benefits declined after 4 weeks of detraining, so maintenance programming matters. ## Limitations - Small sample size and sex imbalance across groups. - Participants were counterbalanced rather than clearly randomized. - No diet control beyond instructions to maintain usual dietary habits. - Both HIIT protocols were cycling-based and supervised, limiting translation to unsupervised bodyweight workouts. - Study may have been too short or under-dosed for body composition and metabolic biomarker changes. ## Safety And Adherence - No adverse events occurred during the experiment. - Training was postponed or rescheduled for low blood pressure, alcohol intoxication, severe lack of sleep, recent meals, or other discomfort. - Long-interval HIIT produced a greater acute heart-rate response than medium-interval HIIT. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/39006847/) (pubmed) - [DOI](https://doi.org/10.7150/ijms.96073) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11241097/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.