# High-Intensity Interval Training Combined with Different Types of Exercises on Cardiac Autonomic Function. An Analytical Cross-Sectional Study in CrossFit(R) Athletes

PMID: 36612955
Journal: International journal of environmental research and public health
Published: 2022 Dec 30
Authors: Morlin MT, da Cruz CJG, Guimarães FER, da Silva RAS, Porto LGG, Molina GE

## Question

How do cardiac autonomic measures in CrossFit athletes compare with endurance athletes?

## Summary

This observational study compared male CrossFit athletes with male triathletes. CrossFit athletes had lower resting parasympathetic and higher sympathetic modulation, less autonomic reactivity to standing, and slower heart-rate recovery at 3 and 5 minutes after maximal exercise, but the design cannot prove CrossFit caused these differences.

## Population

- Healthy male CrossFit and triathlon athletes.
- Sample size: 34
- Age: 20-40 years; group means around 31-33 years
- Sex: Male
- Fitness level: Athletes
- Health status: Healthy after cardiologist evaluation

## Methodology

- Analytical cross-sectional observational study
- Single assessment visit after chronic training exposure
- Exercise physiology laboratory
- Controlled study design.

## Protocol

- Habitual CrossFit/HIITCE.
- Modality: Mixed high-intensity interval training with endurance, strength, and calisthenics.
- Intensity: High intensity; not directly prescribed by the study.
- Session duration: About 7 hours/week total training volume.
- Frequency: About 6 days/week.
- Program length: Average 3.3 years prior exposure.
- Progression: Not reported.
- Habitual triathlon/endurance training.
- Modality: Aerobic endurance training.
- Intensity: Mostly moderate intensity.
- Session duration: About 17 hours/week total volume.
- Frequency: About 7 days/week, often two sessions/day.
- Program length: Average about 4 years prior exposure.
- Progression: Not reported.

## Outcomes

### Resting HRV
Status: worse/safety concern
CrossFit athletes showed lower parasympathetic and higher sympathetic modulation than triathletes.

LF p=0.01; LFn, HFn, and LF/HF p<0.01.

### HRV reactivity
Status: worse/safety concern
CrossFit athletes showed lower reactivity after postural change.

Several LF/LFn/LF-HF measures p=0.01 to 0.02.

### HR recovery
Status: worse/safety concern
Heart-rate recovery was similar at 60 seconds but slower in CrossFit athletes at 180 and 300 seconds.

No 60-second difference; 180 and 300 seconds p<0.01.

## Practical Insights

- Autonomic recovery and training load may deserve attention in frequent high-intensity mixed-modality athletes.
- This paper should inform recovery caution, not causal claims about CrossFit.

## Limitations

- Cross-sectional observational design.
- No sedentary control.
- Male athlete-only convenience sample.
- Training volume differed strongly between groups.

## Safety And Adherence

- No adverse events during testing were reported.
- All athletes received cardiologist evaluation and ECG, and none reported recent overtraining symptoms; CrossFit injury and overtraining risks were discussed but not measured as incident events.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/36612955/) (pubmed)
- [DOI](https://doi.org/10.3390/ijerph20010634) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9819219/) (full text)

## Agent Guidance

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