# HIIT Models in Addition to Training Load and Heart Rate Variability Are Related With Physiological and Performance Adaptations After 10-Weeks of Training in Young Futsal Players

PMID: 33551944
Journal: Frontiers in psychology
Published: 2021
Authors: Campos FS, Borszcz FK, Flores LJF, Barazetti LK, Teixeira AS, Hartmann Nunes RF, Guglielmo LGA

## Question

How do two shuttle HIIT models added to regular futsal training relate to physiological, autonomic, and performance adaptations over 10 weeks?

## Summary

In a small group of under-20 male futsal players, two once-weekly shuttle HIIT models added to regular team training improved aerobic and performance markers. The 86% FIET-speed model appeared more favorable for several running and jump outcomes.

## Population

- Under-20 first division male futsal players from Parana, Brazil.
- Sample size: 11
- Age: 18.5 +/- 1.1 years
- Sex: male only
- Fitness level: competitive youth futsal players
- Health status: not injured and not taking medication affecting outcomes

## Methodology

- parallel two-group longitudinal training study within a team season
- 10 weeks
- under-20 first division futsal team training environment
- Controlled study design.

## Protocol

- HIIT86 shuttle model.
- Modality: shuttle running.
- Work intervals: 15 s running efforts inside 4 min bouts.
- Recovery: 15 s passive rest within bouts; 3 min passive rest between sets.
- Sets or repetitions: 4 sets of 4 min; 8 x 15 s runs per set.
- Intensity: 86% peak speed from FIET.
- Session duration: 16 min set time plus 9 min between-set recovery.
- Frequency: once weekly.
- Program length: 8 HIIT sessions across weeks 2-9 of a 10-week period.
- Progression: intensity individualized by PS_FIET; no volume progression reported.
- HIIT100 shuttle model.
- Modality: shuttle running.
- Work intervals: 15 s running efforts inside 60 s bouts.
- Recovery: 15 s passive rest within bouts; 45 s passive rest between sets.
- Sets or repetitions: 8 sets of 60 s; 2 x 15 s runs per set.
- Intensity: 100% peak speed from FIET.
- Session duration: 8 min set time plus 5.25 min between-set recovery.
- Frequency: once weekly.
- Program length: 8 HIIT sessions across weeks 2-9.
- Progression: intensity individualized by PS_FIET; no volume progression reported.

## Outcomes

### Aerobic fitness
Status: improved
Both models improved VO2peak and treadmill peak speed; HIIT86 was clearer for threshold measures.

HIIT86 had clear improvements in VO2peak, PS_TREADMILL, VT2, and VT1; HIIT100 clearly improved VO2peak and PS_TREADMILL

### RSA and jumps
Status: mixed
Both models showed benefits, with HIIT86 more favorable for RSA_best and squat jump.

HIIT86 more favorable for RSA_best and SJ with >96% probability; discussion reported HIIT86 RSA_best -3.5% and SJ +13.7%

### HRV
Status: improved
Heart-rate variability improved in both groups without clear superiority.

Both groups improved with >98.1% probability

## Practical Insights

- For court-sport athletes, shuttle HIIT can manipulate total hard-running time and change-of-direction load even with the same 15 s effort unit.
- Lower relative speed with more volume may support broader aerobic and neuromuscular adaptations than a shorter 100% FIET model.
- The results are not a stand-alone HIIT prescription for general users because HIIT was embedded in 105 team sessions.

## Limitations

- Very small sample from one male youth team.
- Randomization was not clearly reported.
- No objective external load measures.
- HRV was measured on a single pre/post day.
- Concurrent team training and matches limit attribution.

## Safety And Adherence

- No injuries were reported; inclusion required no injuries and at least 75% attendance.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/33551944/) (pubmed)
- [DOI](https://doi.org/10.3389/fpsyg.2021.636153) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7862135/) (full text)

## Agent Guidance

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