# Effect of high-intensity interval training in young heart transplant recipients: results from two randomized controlled trials

PMID: 32518655
Journal: BMC Sports Science, Medicine and Rehabilitation
Published: 2020
Authors: Nytrøen K, Rolid K, Yardley M, Gullestad L

## Question

Do young heart transplant recipients show greater improvements in aerobic capacity and strength after HIT than with moderate-intensity training or no structured exercise?

## Summary

This hypothesis-generating analysis combined young adult heart transplant recipients from two randomized trials. Supervised treadmill HIT was associated with larger gains in peak oxygen consumption and maximal strength than moderate training or usual activity, but the sample was very small and highly clinical.

## Population

- Young adult heart transplant recipients from two RCTs.
- Sample size: 28
- Age: 18-39 years
- Sex: Mixed; group-specific distributions reported.
- Fitness level: Clinical rehabilitation/maintenance transplant population.
- Health status: De novo or maintenance heart transplant recipients.

## Methodology

- Hypothesis-generating young-subgroup analysis from two randomized controlled trials.
- 9 months in de novo recipients and 1 year in maintenance recipients
- Heart transplant follow-up with supervised community-based exercise.
- Randomized and controlled study design.

## Protocol

- Clinical treadmill HIT.
- Modality: Treadmill.
- Sets or repetitions: Not fully restated in this substudy.
- Intensity: 85-95% peak effort.
- Session duration: Not fully restated in this substudy.
- Frequency: TEX: 3 sessions/week during three 8-week periods; HITTS not fully restated.
- Program length: 9 months in HITTS; 1 year in TEX.
- Progression: Individualized and supervised clinically.
- MICT or usual activity.
- Modality: Treadmill MICT in HITTS; regular activities in TEX control.
- Work intervals: Continuous for MICT.
- Intensity: MICT 60-80% peak effort; TEX control no prescribed training.
- Frequency: HITTS MICT same session amount as HIT; TEX control no prescribed exercise.
- Program length: 9 months or 1 year.

## Outcomes

### Peak oxygen consumption in HITTS young recipients
Status: improved
HIT improved peak oxygen consumption more than MICT.

Difference 4.7 ml/kg/min, 95% CI 0.4 to 9.1, p=0.034.

### Peak oxygen consumption in TEX young recipients
Status: improved
HIT improved peak oxygen consumption more than no specific intervention.

Difference 7.0 ml/kg/min, 95% CI 2.6 to 11.3, p=0.005.

### Maximal strength
Status: improved
Young HIT participants had greater maximal strength gains than comparators in both parent-trial subsets.

HITTS difference 45 Nm p=0.004; TEX difference 41 Nm p=0.031.

### Muscular exercise capacity
Status: no clear change
Muscular exercise capacity differences were not significant.

## Practical Insights

- Clinical high-risk HIIT evidence should be used to define guardrails, not consumer programming.
- Heart transplant status should route users to clinician-led exercise advice.
- Individualized intensity and supervision are central in this population.

## Limitations

- Very small young subgroup
- Combines two different parent RCTs
- Not pediatric despite discussion of young recipients
- Adherence and safety details not separately reported for the subgroup
- Clinical population limits generalizability

## Safety And Adherence

- No young-subgroup adverse-event counts were reported.
- Exercise was professionally supervised or closely monitored in a clinical transplant context.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/32518655/) (pubmed)
- [DOI](https://doi.org/10.1186/s13102-020-00180-1) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7271535/) (full text)

## Agent Guidance

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