# High intensity interval training is associated with greater impact on physical fitness, insulin sensitivity and muscle mitochondrial content in males with overweight/obesity, as opposed to continuous endurance training: a randomized controlled trial

PMID: 29855444
Journal: Journal of Musculoskeletal & Neuronal Interactions
Published: 2018-06-01
Authors: De Strijcker D, Lapauw B, Ouwens DM, Van de Velde D, Hansen D, Petrovic M, Cuvelier C, Tonoli C, Calders P

## Question

Does 10 weeks of low-volume high-intensity interval training produce stronger metabolic and mitochondrial adaptations than continuous aerobic training in overweight/obese men at risk for type 2 diabetes?

## Summary

In sedentary middle-aged men with overweight or obesity and diabetes risk, 10 weeks of twice-weekly high-intensity cycling improved peak fitness, insulin-sensitivity measures, basal respiratory exchange ratio, and muscle mitochondrial content more than a matched-duration continuous aerobic program. The trial was very small and the two exercise modes were not calorie-matched.

## Population

- Sedentary males aged 42-57 years with BMI 28-36 kg/m2 and HbA1c below diabetes threshold.
- Sample size: 16
- Age: 42-57 years
- Sex: Male
- Fitness level: Sedentary
- Health status: Overweight/obesity; at risk for type 2 diabetes

## Methodology

- Randomized controlled two-arm exercise trial
- 10 weeks
- University hospital physiotherapy department
- Randomized and controlled study design.

## Protocol

- High-intensity interval training.
- Modality: Cycling intervals with continuous aerobic segment.
- Work intervals: 15 s.
- Recovery: 45 s.
- Sets or repetitions: 20 sprint bouts per session split into two 10-min blocks.
- Intensity: 100% ventilatory-threshold resistance for weeks 1-5, 110% weeks 6-10; HR >85% peak HR.
- Session duration: 40 min.
- Frequency: 2 sessions/week.
- Program length: 10 weeks.
- Progression: High-intensity bouts increased by 10% from week 6.
- Continuous aerobic training.
- Modality: Continuous cycling and stepping.
- Work intervals: Continuous 10-min blocks.
- Sets or repetitions: Three 10-min continuous blocks.
- Intensity: Heart rate at ventilatory threshold in weeks 1-5, 110% in weeks 6-10.
- Session duration: 40 min.
- Frequency: 2 sessions/week.
- Program length: 10 weeks.
- Progression: Intensity increased 10% from week 6.

## Outcomes

### Peak VO2
Status: improved
Peak VO2 improved after HIT but not continuous aerobic training.

HIT p=0.023; time x group p=0.004.

### Insulin sensitivity
Status: improved
Glucose AUC, insulin AUC, and OGTT composite score improved more after HIT.

AUC glucose and insulin time x group p<0.001; OGTT composite time x group p=0.005.

### Basal RER
Status: improved
Basal RER decreased after HIT, consistent with greater fasting fat oxidation.

HIT p=0.001; CAT p=0.37; time x group p<0.001.

### Mitochondria
Status: improved
Mitochondrial number and surface area increased after HIT at intermyofibrillar and subsarcolemmal sites.

Intermyofibrillar number p<0.001 and surface p=0.001; subsarcolemmal number p=0.004 and surface p=0.001.

### Safety
Status: no clear change
No adverse events were reported during training sessions.

## Practical Insights

- Short 15/45 cycling intervals can produce metabolic adaptations with only two sessions per week when intensity is individualized.
- Clinical-risk users need screening and supervision before high-intensity cycling.
- Claims about insulin sensitivity should acknowledge this was a small all-male trial.

## Limitations

- Very small sample
- All participants were male
- Protocols were not eucaloric
- Baseline insulin sensitivity differed between groups
- OGTT insulin was not measured immediately after the test

## Safety And Adherence

- No adverse events were reported during training sessions.
- One HIT participant attended 18 of 20 sessions because of injury, without detail tying it to training.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/29855444/) (pubmed)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6016496/) (full text)

## Agent Guidance

Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.