# High-Intensity Interval Training Improves Cardiac Autonomic Function in Patients with Type 2 Diabetes: A Randomized Controlled Trial

PMID: 35053064
Journal: Biology
Published: 2022-01-02
Authors: Silva LRB, Gentil P, Seguro CS, de Oliveira JCM, Silva MS, Marques VA, Beltrame T, Rebelo ACS

## Question

Do two HIIT formats improve heart-rate variability and heart-rate recovery more than moderate continuous training in adults with type 2 diabetes?

## Summary

In adults with long-standing type 2 diabetes, 8 weeks of supervised HIIT improved cardiac autonomic markers more than moderate continuous training. The 30-second interval format showed the clearest improvements, but the trial was short and used clinical screening and monitoring.

## Population

- Adults with type 2 diabetes for at least 5 years.
- Sample size: 44
- Age: Group means 58.5-61.2 years
- Sex: Not clearly summarized in extracted text
- Fitness level: Not regularly active in prior 6 months
- Health status: Type 2 diabetes, clinically screened

## Methodology

- Randomized clinical trial
- 8 weeks
- Supervised clinical exercise training with CPET and HRV testing
- Randomized and controlled study design.

## Protocol

- HIIT-30:30 and HIIT-2:2.
- Modality: Aerobic exercise from CPET workload.
- Work intervals: 30 seconds or 2 minutes.
- Recovery: Passive recovery; 30 seconds for HIIT-30:30.
- Sets or repetitions: 20 x 30 seconds or 5 x 2 minutes.
- Intensity: 100% workload at VO2max.
- Session duration: Varied by protocol.
- Frequency: 2 sessions/week.
- Program length: 8 weeks.
- Progression: No clear progression described.
- MICT.
- Modality: Aerobic exercise from CPET workload.
- Work intervals: Continuous.
- Sets or repetitions: 14 minutes continuous.
- Intensity: 70% WLVO2max.
- Session duration: 18 minutes including warm-up/cooldown.
- Frequency: 2 sessions/week.
- Program length: 8 weeks.
- Progression: No clear progression described.

## Outcomes

### HRV
Status: improved
HIIT-30:30 improved R-R interval, pNN50, SDNN, and 2UV% markers more consistently than MICT.

Reported interactions included R-Ri p=.015, SDNN p=.036, and 2UV% p=.029.

### HR recovery
Status: improved
HIIT groups showed faster post-exercise heart-rate recovery kinetics than MICT.

offTAU/offTMR interactions reported; MICT was higher/slower than HIIT groups.

### Resting HR
Status: improved
Resting HR decreased more in HIIT-30:30 than MICT.

Group x time HRrest p=.031; HIIT-30:30 greater reduction than MICT p=.038.

## Practical Insights

- Short-interval 30:30 HIIT may be promising for autonomic function in screened T2D adults.
- Clinical HIIT should include cardiac and glycemic safety workflows.
- Equating distance does not make protocols equivalent in autonomic response.

## Limitations

- Short 8-week intervention.
- No longer HRV monitoring 12 or 24 hours after sessions.
- No nutritional control.
- Higher-risk patients were excluded during CPET screening.
- Attendance-based exclusions may bias toward adherent participants.

## Safety And Adherence

- Exercise screening excluded participants with unstable angina, uncontrolled arrhythmias, low exercise capacity, or abnormal blood pressure response.
- Session monitoring included blood pressure, heart rate, and glycemia.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/35053064/) (pubmed)
- [DOI](https://doi.org/10.3390/biology11010066) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8773290/) (full text)

## Agent Guidance

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