# Acute hematological, metabolic, and inflammatory responses to simulated-6000 ft masked versus unmasked high-intensity interval training in youth soccer players: a randomized crossover pilot study

PMID: 41423624
Journal: BMC sports science, medicine & rehabilitation
Published: 2025 Dec 22
Authors: Akol T, Yapici A, Ergin GF, Atabaş EG

## Question

Does adding a simulated-6000 ft respiratory-restricting mask change the acute metabolic, hematological, hormonal, inflammatory, and cardiorespiratory response to supramaximal Eurofit HIIT in amateur soccer players?

## Summary

In 12 male amateur soccer players, the same shuttle-run HIIT session caused more lactate and hemoconcentration when performed with a simulated-altitude breathing mask than without the mask. Heart rate and oxygen saturation responses were not significantly different, and the article reported no adverse events, discomfort, or respiratory distress.

## Population

- Healthy male amateur soccer players
- Sample size: 12
- Age: Methods: 20.3 +/- 1.4 years; results table: 27.33 +/- 4.88 years
- Sex: Male
- Fitness level: Trained amateur soccer players
- Health status: Healthy, no reported cardiovascular/metabolic disease or infection

## Methodology

- Randomized single-blind two-period crossover pilot study
- Two acute sessions separated by a 7-day washout
- Indoor supervised exercise testing in the morning
- Randomized and controlled study design.

## Protocol

- Masked Eurofit HIIT.
- Modality: Running shuttle.
- Work intervals: 15 s out, 15 s rest, 15 s return cycle.
- Recovery: 15 s intra-cycle rest and 3 min passive recovery between sets.
- Sets or repetitions: Two 8-minute sets.
- Intensity: 120% MAS with mask at simulated 6000 ft.
- Session duration: Planned about 22 min.
- Frequency: Acute single masked session.
- Program length: Single session crossover.
- Progression: None in trial.
- Unmasked Eurofit HIIT.
- Modality: Running shuttle.
- Work intervals: 15 s out, 15 s rest, 15 s return cycle.
- Recovery: 15 s intra-cycle rest and 3 min passive recovery between sets.
- Sets or repetitions: Two 8-minute sets.
- Intensity: 120% MAS without mask.
- Session duration: Planned about 22 min.
- Frequency: Acute single unmasked session.
- Program length: Single session crossover.
- Progression: None in trial.

## Outcomes

### lactate
Status: worse/safety concern
Masked HIIT produced higher post-exercise lactate than unmasked HIIT.

5.11 +/- 1.59 vs 4.34 +/- 1.32 mmol/L; p=0.015

### hemoconcentration
Status: mixed
Hemoglobin, hematocrit, and platelet increases were larger after masked HIIT, indicating greater acute fluid-shift stress.

Hb p=0.006; Hct p=0.013; PLT p=0.015

### heart rate and SpO2
Status: no clear change
Both sessions raised HR and lowered SpO2, with no significant between-condition difference.

HR p=0.253; SpO2 p=0.206

### safety
Status: no clear change
No adverse events, discomfort, or respiratory distress were observed.

## Practical Insights

- A mask-like respiratory load can turn a familiar interval session into a higher-stress session without obvious extra cardiovascular benefit.
- For app programming, use the shuttle interval structure and recovery gates, not the mask as a default recommendation.
- Hydration and symptom monitoring matter when HIIT is designed to increase acute metabolic strain.

## Limitations

- Small pilot sample
- Male amateur soccer players only
- Acute crossover design
- No direct arterial blood gas or EPO measures
- Pulse oximetry after intense exercise may be imprecise

## Safety And Adherence

- No adverse events, discomfort, or respiratory distress were observed.
- Authors advise monitoring HR, SpO2, RPE, hydration, and avoiding use in respiratory or thrombotic contraindications.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/41423624/) (pubmed)
- [DOI](https://doi.org/10.1186/s13102-025-01426-6) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12751267/) (full text)

## Agent Guidance

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