# Heart Rate Variability Monitoring During Strength and High-Intensity Interval Training Overload Microcycles

PMID: 31178746
Journal: Frontiers in Physiology
Published: 2019 May 22
Authors: Schneider C, Wiewelhove T, Raeder C, Flatt AA, Hoos O, Hottenrott L, Schumbera O, Kellmann M, Meyer T, Pfeiffer M, Ferrauti A

## Question

Can daily HRV monitoring identify fatigue and recovery during strength and HIIT overload microcycles in trained athletes?

## Summary

This athlete overload study tracked daily heart-rate variability during short periods of strength or HIIT overload. In the HIIT arm, performance dipped after overload and rebounded after recovery, while standing HR and HRV changed, but HRV markers were not consistent individual performance predictors.

## Population

- Trained strength athletes and team-sport athletes; HIIT arm was team-sport trained
- Sample size: 37
- Age: HIIT mean 27.1 +/- 2.8 years
- Sex: HIIT 9 women/9 men; strength 7 women/12 men
- Fitness level: Trained athletes
- Health status: Screened healthy

## Methodology

- Repeated-measures overload microcycle study with separate strength and HIIT arms
- 14 days including baseline, 6-day overload, and 4-day recovery
- Sports science laboratory and outdoor track

## Protocol

- HIIT overload microcycle.
- Modality: Track running, shuttle runs, and sprints.
- Work intervals: 4 min, 2 min, 5 sec, or 30 sec depending on session.
- Recovery: 25 sec to 5 min depending on session.
- Sets or repetitions: 11 sessions over 6 days.
- Intensity: 80-90% VIFT or all-out sprints.
- Session duration: About 35 minutes.
- Frequency: Up to two sessions/day over 6 days.
- Program length: 6-day overload plus 4-day recovery.
- Progression: Overload by frequency and density.
- Strength overload arm.
- Modality: Strength training overload.
- Program length: Same study window.

## Outcomes

### RSA
Status: mixed
HIIT RSA performance decreased immediately after overload and increased after recovery.

Mean peak velocity Post1 -0.18 m/s; Post4 +0.18 m/s.

### Standing HRV
Status: mixed
Standing HR decreased and standing Ln RMSSD increased during overload/recovery, then reversed.

Standing HR dpre about -0.50 to -0.59; Ln RMSSD dpre about 0.38 to 0.47.

### Supine HRV
Status: no clear change
Supine measures were less responsive than standing measures.

### HRV prediction
Status: unclear
Associations between HR/HRV and performance were weak or inconsistent.

## Practical Insights

- Short overload blocks can transiently depress performance and require recovery.
- Standing HRV may be more informative than supine HRV in this context, but not deterministic for individuals.

## Limitations

- Athlete-only overload design.
- No no-overload control group.
- Short study window.
- HRV-influencing behaviors not fully controlled.
- Adverse-event reporting limited.

## Safety And Adherence

- Adverse events were not systematically reported.
- One participant dropped out due to injury among eligible participants; the text available did not clearly attribute this to the HIIT arm.
- Participants had preliminary health exams including resting and exercise ECG to exclude cardiovascular, pulmonary, and orthopedic disease.
- The protocol was a dense supervised overload microcycle for trained athletes.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/31178746/) (pubmed)
- [DOI](https://doi.org/10.3389/fphys.2019.00582) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6538885/) (full text)

## Agent Guidance

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