# Effect of aquatic high-intensity interval training on exercise capacity in people with chronic conditions: a systematic review and meta-analysis

PMID: 38022764
Journal: BMJ Open Sport & Exercise Medicine
Published: 2023
Authors: Bunæs-Næss H, Kvæl LAH, Nilsson BB, Heywood S, Heiberg KE

## Question

Does aquatic HIIT improve exercise capacity in adults with chronic conditions compared with control, land-based HIIT, or aquatic moderate-intensity continuous training?

## Summary

This review found that aquatic HIIT improved exercise capacity compared with non-exercise controls and had similar effects to land-based HIIT, with a small benefit over aquatic moderate continuous training. Adherence was generally high, but adverse-event reporting was sparse.

## Population

- Adults with chronic musculoskeletal, respiratory, cardiovascular, metabolic, or neurological conditions
- Sample size: 868
- Age: Adults 18 years and older
- Sex: Mostly female; 640 of 868 participants female
- Fitness level: Clinical populations with varied baseline capacity
- Health status: Chronic conditions including low back pain, knee osteoarthritis, fibromyalgia, COPD/asthma, hypertension/PAD, dyslipidemia, type 2 diabetes, PCOS, obesity, spinal cord injury, multiple sclerosis, and stroke

## Methodology

- Systematic review and meta-analysis of randomized and nonrandomized clinical trials
- Included trials lasted at least 6 weeks
- Aquatic exercise trials in chronic conditions
- Controlled study design.

## Protocol

- Aquatic HIIT.
- Modality: Water-based interval exercise.
- Work intervals: Varied by trial; examples included 30-second all-out swimming, 2-minute intense bouts, 3-4-minute deep-water running intervals, and 4-minute rounds.
- Recovery: Varied by trial.
- Sets or repetitions: Varied by trial.
- Intensity: Defined by RPE >=14, HRmax >=77%, VO2 >64% VO2peak/max capacity, or study-defined HIIT with monitored intensity.
- Session duration: Often 45-60 minutes.
- Frequency: Often 2-3 sessions per week.
- Program length: 8-16 weeks in many trials; minimum 6 weeks.
- Progression: Varied by trial.
- Control, land-based HIIT, or aquatic MICT.
- Modality: Non-exercise control, land-based HIIT, or aquatic continuous training depending on trial.
- Work intervals: Varied or continuous.
- Recovery: Varied.
- Sets or repetitions: Varied.
- Intensity: Comparator-specific.
- Session duration: Varied.
- Frequency: Varied.
- Program length: At least 6 weeks.
- Progression: Varied.

## Outcomes

### Capacity vs control
Status: improved
Aquatic HIIT improved exercise capacity compared with non-exercise control.

10 RCTs; SMD 0.78, 95% CI 0.48 to 1.08, P < 0.00001, I2 = 52%, moderate certainty

### Capacity vs LBHIIT
Status: no clear change
Aquatic HIIT did not significantly differ from land-based HIIT.

4 RCTs; SMD 0.28, 95% CI -0.04 to 0.60, P = 0.08, I2 = 0%, moderate certainty

### Capacity vs AMICT
Status: improved
Aquatic HIIT produced a small benefit over aquatic moderate-intensity continuous training.

4 RCTs; SMD 0.45, 95% CI 0.10 to 0.80, P = 0.01, I2 = 0%, moderate certainty

### Adherence
Status: improved
Reported aquatic HIIT adherence was high across trials that reported it.

12 trials reported adherence; AHIIT 84-100%, LBHIIT 85-100%

### Safety
Status: unclear
Adverse events were sparsely reported; reported events did not show a clear excess versus comparators.

4 trials reported adverse events; examples included asthmatic attacks of unclear group, medical consultations, muscle/joint pain, fatigue withdrawal, and two trials with no AEs

## Practical Insights

- Aquatic HIIT may be useful for chronic-condition populations who benefit from buoyancy or reduced joint load.
- Most protocols were supervised and group-based, limiting direct app-only translation.
- Sparse adverse-event reporting means safety claims should be cautious.

## Limitations

- Heterogeneity in AHIIT versus control comparisons.
- Methodological concerns and limited blinding.
- Adverse-event reporting was sparse.
- Follow-up periods were limited.
- Functional and quality-of-life persistence was not fully explored.

## Safety And Adherence

- Only 4 trials reported adverse events.
- Reported events included asthmatic attacks, knee pain/dyspnoea consultations, muscle/joint pain, one fatigue withdrawal in control, and two trials with no adverse events.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/38022764/) (pubmed)
- [DOI](https://doi.org/10.1136/bmjsem-2023-001639) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10649609/) (full text)

## Agent Guidance

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