# Comparing acute effects of HIIT and REHIT on salivary BDNF: a randomized controlled trial

PMID: 41184371
Journal: Scientific Reports
Published: 2025-11-03
Authors: Evelis K, Kolesovs A, Rostoka E, Plakane L

## Question

Do acute HIIT and REHIT sessions differ in their effects on salivary BDNF and lactate in young adults?

## Summary

In low-to-moderately active young adults, one acute cycling HIIT session raised blood lactate and increased salivary BDNF, while an all-out reduced-exertion HIIT session caused an even larger lactate response but did not increase salivary BDNF. Lactate changes did not correlate with BDNF changes.

## Population

- Low-to-moderately active young adults
- Sample size: 60
- Age: Mean 24 years, SD 3
- Sex: 37 female, 23 male
- Fitness level: Low to moderately active; exercise up to 3 times per week
- Health status: No medical condition limiting exercise; non-smokers

## Methodology

- Block-randomized controlled clinical trial with acute pre-post measures
- Single acute session
- Sports Physiology Laboratory, University of Latvia
- Randomized and controlled study design.

## Protocol

- Acute cycling HIIT.
- Modality: Cycle ergometer.
- Work intervals: 90 seconds.
- Recovery: 90 seconds complete rest.
- Sets or repetitions: 5 cycles.
- Intensity: 80-90% theoretical HRmax.
- Session duration: 15-minute main protocol plus 5-minute warm-up, 1-minute rest, and 5-minute cool-down.
- Frequency: Single session.
- Program length: Acute.
- REHIT and seated video control.
- Modality: Cycle ergometer for REHIT; seated video for control.
- Work intervals: REHIT: 15 seconds all-out.
- Recovery: REHIT: 200 seconds complete rest plus 10 seconds light cycling prep.
- Sets or repetitions: REHIT: 4 cycles.
- Intensity: REHIT all-out at resistance 3.75% body weight.
- Session duration: REHIT 15-minute main protocol plus warm-up/rest/cool-down; control 15-minute video.
- Frequency: Single session.
- Program length: Acute.

## Outcomes

### Lactate
Status: improved
Both exercise groups increased lactate; REHIT increased lactate more than HIIT.

Group x time F(2,56)=115.15, P < 0.001; HIIT 1.70 +/- 0.70 to 8.98 +/- 2.87 mmol/L; REHIT 1.66 +/- 0.60 to 12.87 +/- 2.27

### BDNF
Status: mixed
There was no significant group-by-time interaction, but within-group salivary BDNF increased only after HIIT.

Interaction chi-square(2)=2.80, P = 0.247; HIIT median 143 to 179 pg/mL, +25.2%, P = 0.025; REHIT P = 0.916; control P = 0.164

### Lactate-BDNF
Status: no clear change
Lactate and BDNF changes were not significantly correlated.

Correlations nonsignificant in all groups

### Glucose
Status: mixed
A time effect was observed, but post-hoc group changes were not significant.

No significant post-hoc group changes reported

## Practical Insights

- An acute 5 x 90-second HIIT cycling protocol may elicit salivary BDNF changes in young adults.
- A larger lactate response from all-out REHIT did not translate into higher salivary BDNF.
- This is biomarker evidence, not evidence for training adaptation or cognitive outcomes.

## Limitations

- Acute single-session design.
- Surrogate salivary biomarker outcome.
- Heart rate was not recorded for HIIT, limiting confirmation of intensity.
- Saliva collection length varied.
- Food abstinence was self-reported and not monitored.
- No blood BDNF samples.

## Safety And Adherence

- One participant discontinued due dizziness/discomfort from blood collection.
- No other adverse effects reported in extracted text.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/41184371/) (pubmed)
- [DOI](https://doi.org/10.1038/s41598-025-22209-6) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12583766/) (full text)

## Agent Guidance

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