Aerobic exercise improves a vascular marker without demonstrating fewer cardiovascular events

What the researchers measured

This systematic review brings together 72 randomized studies assessing the effect of aerobic exercise on endothelial function. The endothelium is the layer of cells lining the inside of blood vessels. The primary outcome was the change in brachial artery flow-mediated dilation, known as FMD.

This measurement provides information about the artery’s response to increased blood flow. It allows researchers to study one aspect of vascular function, but does not count heart attacks or strokes.

The researchers also examined blood markers, blood pressure, cardiorespiratory fitness, body composition, glucose metabolism and lipid profiles. The supplied abstract does not detail the populations, comparators or program durations.

A vascular improvement, not a measured clinical risk

The analysis reports a statistically significant mean difference in FMD of 2.35 percentage points. This finding supports a favorable effect of aerobic exercise on this marker. However, the abstract provides neither a confidence interval nor a measure of heterogeneity to assess the precision and variability of the effect.

The authors associate this improvement with an estimated 24% reduction in cardiovascular risk. This interpretation should not be read as a reduction directly demonstrated by the included trials. Nor does it allow us to calculate how many events would be prevented for a given person.

Possible explanations, without an established mechanism

The meta-regression identifies relationships between improvements in FMD and changes in weight, fat mass, blood pressure, maximal oxygen uptake and insulin.

These relationships between study results suggest avenues for understanding vascular adaptations. They do not demonstrate that each of these changes causes the improvement in FMD, or that together they explain the effect in every participant.

For your own training, this review mainly provides evidence concerning vascular function. The available abstract does not allow you to choose a training intensity, frequency or duration, or determine which groups benefit most.

What we can take away

Aerobic exercise improves a marker of vascular function in this review of randomized trials. The estimated reduction in cardiovascular risk remains distinct from a directly measured clinical benefit.