# Effects of aquatic high-intensity interval training and moderate-intensity continuous training on central hemodynamic parameters, endothelial function and aerobic fitness in inactive adults

PMID: 35646132
Journal: Journal of Exercise Science and Fitness
Published: 2022 Jul
Authors: Tang S, Huang W, Wang S, Wu Y, Guo L, Huang J, Hu M

## Question

How do 6 weeks of aquatic HIIT and moderate-intensity continuous swimming affect central hemodynamics, endothelial function, and aerobic fitness in inactive adults?

## Summary

In inactive adults, 6 weeks of aquatic HIIT and aquatic moderate continuous training both improved some body composition and vascular measures. HIIT used only 6 minutes of hard swimming per session and improved VO2max and flow-mediated dilation, while MICT produced stronger blood-pressure and resting heart-rate reductions.

## Population

- 31 inactive adults randomized; 26 analyzed after attendance exclusion.
- Sample size: 31
- Age: About 39-42 years by analyzed group mean
- Sex: Mixed
- Fitness level: Inactive
- Health status: No severe respiratory disease, kidney dysfunction, or cardiovascular disease

## Methodology

- Randomized controlled active-comparator trial
- 6 weeks
- Aquatic exercise training with land and water warm-up
- Randomized and controlled study design.

## Protocol

- Aquatic HIIT.
- Modality: Breaststroke swimming.
- Work intervals: 30 s.
- Recovery: 60 s rest.
- Sets or repetitions: 12 bouts.
- Intensity: 75-90% HRmax week 1; 95% HRmax and RPE 15-18/20 weeks 2-6.
- Session duration: 18-20 min training segment; about 53-55 min including warm-up/cool-down.
- Frequency: 3 sessions/week.
- Program length: 6 weeks.
- Progression: Intensity increased after week 1.
- Aquatic MICT.
- Modality: Breaststroke swimming.
- Work intervals: 30 min continuous.
- Sets or repetitions: One continuous bout.
- Intensity: 70-75% HRmax and RPE 12-14/20.
- Session duration: About 65 min including warm-up/cool-down.
- Frequency: 3 sessions/week.
- Program length: 6 weeks.
- Progression: Target intensity checked every 5 min.

## Outcomes

### VO2max
Status: improved
HIIT improved absolute and relative VO2max; MICT did not.

HIIT relative VO2/kg 30.9 +/- 6.2 to 33.5 +/- 6.4; group x time p<0.05.

### FMD
Status: improved
FMD improved after aquatic exercise, with clearer significance in HIIT.

HIIT FMD 3.56 +/- 1.67 to 4.94 +/- 2.10, p<0.05; MICT p=0.072.

### Blood pressure
Status: mixed
MICT reduced central and peripheral blood pressure more consistently than HIIT.

MICT reduced bSBP, bDBP, aSBP, aDBP, aMP, and HR; HIIT reduced aMP only.

### Body composition
Status: improved
Both groups reduced weight, BMI, and fat mass; HIIT also increased skeletal muscle and reduced fat percentage.

HIIT fat % p<0.001 and skeletal muscle p<0.01; MICT fat % not significant.

## Practical Insights

- Aquatic HIIT delivered 6 minutes of hard work per session with measurable aerobic and endothelial gains.
- MICT may be a better short-term aquatic option when blood-pressure reduction is the priority.
- Water-based HR targets may need validation for each user.

## Limitations

- Small sample.
- Short intervention.
- Five participants excluded for low attendance.
- Land-derived HRmax may not map cleanly to water exercise.
- No explicit adverse-event reporting.

## Safety And Adherence

- No explicit adverse-event report was found.
- Participants with severe respiratory disease, kidney dysfunction, or cardiovascular disease were excluded.
- Floats could be used to assist swimming.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/35646132/) (pubmed)
- [DOI](https://doi.org/10.1016/j.jesf.2022.04.004) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9123277/) (full text)

## Agent Guidance

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