HIIT beats steady cardio for artery flexibility, but only by a whisker

Arterial stiffness is regarded as an independent predictor of cardiovascular events and death from any cause, which makes it one of the more consequential things exercise can change. Physical activity is known to help keep arteries compliant, but the practical question for anyone planning their cardio is whether the style of training matters. High-intensity interval training and moderate-intensity continuous training are the two dominant approaches, and head-to-head evidence on arterial stiffness has been scattered across many small trials. This meta-analysis set out to compare them directly on one pooled estimate.

The authors searched five electronic databases from their inception to January 10, 2025 for randomised controlled trials comparing high-intensity interval training against moderate-intensity continuous training in adults. The outcome was pulse wave velocity, the standard measure of arterial stiffness, which gauges how fast the pressure wave travels along the arteries; stiffer vessels transmit it faster. Twenty-two studies with a combined 619 participants met the criteria, and changes before and after the training interventions were pooled and compared between the two exercise styles.

HIIT came out ahead: compared with moderate continuous training, it produced a greater reduction in pulse wave velocity of 0.10 m/s. The advantage also held for carotid-femoral pulse wave velocity, again by 0.10 m/s. Both differences reached statistical significance. The margin is modest in absolute terms, and the analysis speaks to the gap between the two training styles rather than to the total improvement either style delivers on its own, which this comparison was not designed to size.

The direction of the result fits the broader picture that vigorous exercise drives strong cardiovascular adaptations, and it extends earlier work by pooling 22 randomised comparisons into a single estimate. What it adds is a size: the edge for intervals over steady work is real but small. Open questions remain, including how long the advantage persists after training stops, whether particular ages or fitness levels benefit more, and how much interval work is needed, none of which this analysis answers.

If you already favour interval sessions, this is evidence they are doing slightly more for your arteries than the same commitment to steady cardio would. If intervals are not for you, the finding is no reason to abandon moderate continuous training: the comparison concerns the gap between two effective approaches, not a verdict that one is useless. Arterial stiffness predicts cardiovascular events and mortality, so any training that improves it is working on something that genuinely matters.