# High-Intensity Interval Training Improves Markers of Oxidative Metabolism in Skeletal Muscle of Individuals With Obesity and Insulin Resistance

PMID: 30429793
Journal: Frontiers in Physiology
Published: 2018-10-31
Authors: de Matos MA, Vieira DV, Pinhal KC, Lopes JF, Dias-Peixoto MF, Pauli JR, de Castro Magalhães F, Little JP, Rocha-Vieira E, Amorim FT

## Question

Does eight weeks of HIIT alter blood and skeletal-muscle markers related to insulin resistance, MAPK signaling, mitochondrial biogenesis, and oxidative metabolism in obese adults with and without insulin resistance?

## Summary

In obese adults with and without insulin resistance, eight weeks of supervised cycling HIIT increased VO2peak and peak power and improved several skeletal-muscle signaling and oxidative metabolism markers. Insulin resistance by HOMA-IR improved in the insulin-resistant obese group, while fat mass did not decrease.

## Population

- Physically inactive adults with obesity, with and without insulin resistance; lean controls measured at baseline only.
- Sample size: 26
- Age: About 29-32 years across groups
- Sex: 9 men and 17 women total; obese HIIT groups included 6 men and 11 women
- Fitness level: Sedentary
- Health status: Obesity with or without insulin resistance; diabetes and glucose intolerance excluded

## Methodology

- Nonrandomized pre-post intervention with baseline lean control comparison
- 8 weeks
- Supervised laboratory cycle-ergometer HIIT with blood testing and vastus lateralis biopsy
- Controlled study design.

## Protocol

- Obesity phenotype cycling HIIT.
- Modality: Cycle ergometer.
- Work intervals: 60 s.
- Recovery: 60 s active recovery at 30 W.
- Sets or repetitions: 8-12 bouts.
- Intensity: 80-110% peak power.
- Session duration: 16-28 min including 2-min warm-up and 2-min cooldown.
- Frequency: 3 sessions/week.
- Program length: 8 weeks.
- Progression: Bouts and intensity progressed; week-4 work-rate test adjusted intensity.
- Baseline lean controls.
- Program length: Baseline comparison only.

## Outcomes

### VO2peak
Status: improved
VO2peak and peak power increased in both obese groups.

VO2peak and peak power p<0.0001; OB 27.2 to 30.5 and OBR 24.8 to 27.4 ml/kg/min.

### HOMA-IR
Status: mixed
Insulin-resistant obese participants improved fasting insulin, HOMA-IR, and HOMA-beta; non-insulin-resistant obese participants did not.

OBR insulin p=0.004, HOMA-IR p=0.02, HOMA-beta p=0.01; HOMA-IR 4.4 to 3.5 in Table 3.

### Muscle signaling
Status: improved
IRS and Akt phosphorylation increased in both obese groups.

IRS Tyr612 p=0.04; Akt Ser473 p=0.03.

### Oxidative proteins
Status: improved
COX-IV and beta-HAD increased in skeletal muscle after HIIT.

COX-IV p=0.006; beta-HAD p=0.046.

### Body fat
Status: no clear change
Fat mass did not significantly decrease; body mass, BMI, and waist circumference did not change.

No significant effect on body mass, BMI, waist circumference, or fat mass; OB body fat percentage decreased p=0.001.

### Lipids
Status: mixed
Total cholesterol and LDL decreased overall, while HDL, VLDL, and triglycerides did not change.

Total cholesterol p=0.03; LDL p=0.03; HDL/VLDL/triglycerides p>0.05.

## Practical Insights

- Fitness and muscle oxidative adaptations may occur without fat loss.
- Sixty-second intervals with equal recovery are a practical structure, but exact replication requires cycle peak-power testing.
- Metabolic-health claims should specify screened obese adults and distinguish HOMA-IR from clamp-measured insulin sensitivity.

## Limitations

- Small sample
- Nonrandomized groups
- No non-exercising obese control over time
- Surrogate muscle protein outcomes
- No hyperinsulinemic euglycemic clamp
- Insulin signaling measured without insulin stimulation
- Menstrual-cycle phase not controlled
- Limited biopsy tissue for some western blots

## Safety And Adherence

- No explicit adverse-event results were reported.
- Participants were medically screened for diabetes, glucose intolerance, chronic disease, relevant medications, and smoking.
- HR and RPE were monitored during supervised sessions.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/30429793/) (pubmed)
- [DOI](https://doi.org/10.3389/fphys.2018.01451) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6220130/) (full text)

## Agent Guidance

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