# Six weeks of high-intensity interval training enhances contractile activity induced vascular reactivity and skeletal muscle perfusion in older adults

PMID: 34562202
Journal: GeroScience
Published: 2021 Dec
Authors: Herrod PJJ, Atherton PJ, Smith K, Williams JP, Lund JN, Phillips BE

## Question

Does 6 weeks of time-efficient HIIT improve skeletal muscle microvascular responsiveness to acute contractile activity in healthy older adults?

## Summary

This randomized controlled trial tested 6 weeks of fully supervised cycle-ergometer HIIT in healthy older adults aged 65-85 years. HIIT improved anaerobic threshold, dynamic exercise capacity, systolic blood pressure, and microvascular blood-volume response to a bout of knee-extension exercise, while the no-intervention control group did not change. The study had 100% HIIT session compliance but used a small, carefully screened healthy sample.

## Population

- Twenty-five healthy older adults aged 65-85 years randomized to HIIT or no-intervention control; 23 included in final analysis.
- Sample size: 25
- Age: HIIT 70 +/- 3 years; control 72 +/- 6 years
- Sex: HIIT 5 men/8 women; control 7 men/5 women
- Fitness level: Not currently in a formal exercise regime.
- Health status: Healthy older adults with BMI 18-30 and no active CVD, uncontrolled hypertension, diabetes, early family CVD death, or Sonovue sensitivity.

## Methodology

- Randomized controlled trial comparing 6-week fully supervised HIIT with a no-intervention control period.
- 6 weeks.
- Laboratory-based supervised cycle-ergometer HIIT with clinical safety monitoring and vascular imaging.
- Randomized and controlled study design.

## Protocol

- Supervised cycle HIIT.
- Modality: Cycle ergometer.
- Work intervals: 5 x 1-minute high-intensity cycling efforts.
- Recovery: Recovery period included but not specified in the text read.
- Sets or repetitions: 5 efforts per session.
- Intensity: High intensity; 10% increase after 3 weeks if modified Borg RPE <=8.
- Session duration: Approximately 15 minutes.
- Frequency: 3 sessions per week.
- Program length: 6 weeks.
- Progression: RPE-guided 10% intensity increase after session 9 when indicated.
- No-intervention control.
- Modality: No exercise intervention.
- Program length: 6-week control period.

## Outcomes

### Microvascular responsiveness
Status: improved
HIIT increased microvascular blood-volume response to acute knee-extension exercise; control did not change.

HIIT 1.8 +/- 0.6 to 2.3 +/- 0.8, p < 0.01; control p = 0.94; interaction p < 0.01.

### Anaerobic threshold
Status: improved
HIIT increased anaerobic threshold.

13.2 +/- 3.4 to 15.3 +/- 3.8 mL/kg/min, p < 0.01.

### Dynamic exercise capacity
Status: improved
HIIT increased peak wattage during CPET.

145 +/- 60 to 159 +/- 59 W, p < 0.01.

### Blood pressure
Status: mixed
HIIT reduced systolic blood pressure but did not significantly change diastolic blood pressure.

SBP 142 +/- 16 to 133 +/- 11 mmHg, p < 0.01; DBP time p = 0.27 and interaction p = 0.76.

## Practical Insights

- Short cycling HIIT can improve fitness and vascular responsiveness in carefully screened older adults.
- Clinical safety monitoring in this study was much higher than typical consumer settings.
- Microvascular benefits are mechanistic and need clinical outcome confirmation.

## Limitations

- Small sample.
- Healthy older adults only.
- Strict exclusions for diabetes, active CVD, uncontrolled hypertension, and high BMI.
- CEUS chronic baseline comparisons need validation.
- Clinical significance of MBV response change is unknown.

## Safety And Adherence

- All HIIT sessions were supervised with 12-lead ECG, BP, and pulse oximetry.
- One MBF measurement failed because of cannula failure causing contrast extravasation.
- No exercise adverse events were reported in the read text.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/34562202/) (pubmed)
- [DOI](https://doi.org/10.1007/s11357-021-00463-6) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8602610/) (full text)

## Agent Guidance

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