# Longer Work/Rest Intervals During High-Intensity Interval Training (HIIT) Lead to Elevated Levels of miR-222 and miR-29c

PMID: 29719514
Journal: Frontiers in physiology
Published: 2018
Authors: Schmitz B, Rolfes F, Schelleckes K, Mewes M, Thorwesten L, Krüger M, Klose A, Brand SM

## Question

Do workload-matched 4 x 30-second and 8 x 15-second all-out running HIIT protocols differ in their effects on circulating miR-222/miR-29c and performance adaptations?

## Summary

In healthy moderately trained young adults, two workload-matched running HIIT formats both improved maximal speed and heart-rate recovery over 4 weeks. The longer 4 x 30-second format, but not the 8 x 15-second format, improved speed at individual anaerobic threshold and produced acute elevations in miR-222 and miR-29c, suggesting work-rest structure may affect molecular and performance responses.

## Population

- Healthy moderately trained young adult physical education students
- Sample size: 63
- Age: 22.0 +/- 1.7 years
- Sex: Females and males; analyzed baseline table included 39 women and 14 men
- Fitness level: Moderately trained
- Health status: Healthy with required health certificate

## Methodology

- Randomized controlled intervention comparing two active HIIT protocols
- 4 weeks
- Indoor 200-m running track and supervised training
- Randomized and controlled study design.

## Protocol

- 4 x 30 all-out running HIIT.
- Modality: Running.
- Work intervals: 30 seconds all-out.
- Recovery: 30 seconds active recovery at warm-up speed.
- Sets or repetitions: 4 bouts.
- Intensity: All-out.
- Session duration: About 14 minutes including warm-up.
- Frequency: 2 sessions/week.
- Program length: 4 weeks.
- Progression: None.
- 8 x 15 all-out running HIIT.
- Modality: Running.
- Work intervals: 15 seconds all-out.
- Recovery: 15 seconds active recovery at warm-up speed.
- Sets or repetitions: 8 bouts.
- Intensity: All-out.
- Session duration: About 14 minutes including warm-up.
- Frequency: 2 sessions/week.
- Program length: 4 weeks.
- Progression: None.

## Outcomes

### miRNA acute response
Status: mixed
Acute miR-222 and miR-29c increased after 4 x 30 HIIT but not after 8 x 15 HIIT.

Both p<0.01 in 4 x 30

### resting miRNAs
Status: improved
Both groups had increased resting miR-222 and miR-29c after training.

All p<0.001

### speed at IAT
Status: improved
Speed at individual anaerobic threshold improved only in the 4 x 30 group.

+3.6%; p<0.0132

### HR recovery
Status: improved
Heart-rate recovery improved by more than 24% in both HIIT groups.

Both p<=0.0002

## Practical Insights

- Equal total work can produce different adaptations depending on whether reps are 30 seconds or 15 seconds.
- 4 x 30 all-out can be a compact threshold-focused template for prepared users.
- Use miRNA findings internally as mechanistic context, not frontend promise.

## Limitations

- Moderately trained young adults only
- Molecular surrogate outcomes
- Injury/illness dropouts not detailed
- No control without HIIT
- Outside training and diet not fully controlled

## Safety And Adherence

- Injury/illness during training was an exclusion/dropout reason, but details and relatedness were not reported.
- All-out running in moderately trained students should not be generalized to unscreened beginners.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/29719514/) (pubmed)
- [DOI](https://doi.org/10.3389/fphys.2018.00395) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5913345/) (full text)

## Agent Guidance

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