37 Studies Compared Workouts — This Exercise Stood Out For Heart Health
Most people think about cardio in terms of calories, endurance, or heart rate zones. You go for a run, take a cycling class, spend 45 minutes on the elliptical, and assume your heart is getting what it needs. And to some extent, it is. But there’s another part of cardiovascular health that rarely enters the conversation: the health of your blood vessels themselves.
Your arteries are not passive plumbing. They’re living tissue that constantly responds to stress, movement, inflammation, sleep, blood sugar, and blood flow. Healthy vessels expand easily when blood needs to move through them. Less healthy vessels become stiffer, less responsive, and more inflamed over time, long before a heart attack or diagnosis ever happens.
One of the clearest ways researchers measure this is through something called endothelial function, which reflects how well the inner lining of blood vessels can dilate and regulate circulation. And according to a large new analysis published in the European Heart Journal, the type of exercise that seems to improve it most may not be the steady-state cardio many people default to.
The large exercise analysis that compared multiple workout styles
Researchers analyzed data from 37 studies involving nearly 7,000 adults with cardiovascular disease, including coronary artery disease and chronic heart failure. Instead of comparing just one type of exercise to another, they used a network meta-analysis, which allowed them to evaluate several training styles simultaneously.
The studies looked at different forms of exercise: moderate-intensity aerobic exercise like brisk walking or continuous cycling, high-intensity interval exercise (HIIE), resistance training, and combined aerobic-plus-strength programs. Researchers then compared how each affected flow-mediated dilation (FMD), a widely used marker of endothelial function and vascular flexibility.
In simple terms, FMD measures how effectively an artery expands when blood flow increases. Better dilation generally signals healthier blood vessels and better nitric oxide production, both of which matter for long-term cardiovascular health.
Moderate continuous cardio improved vascular function. Combined training helped too. But high-intensity interval exercise consistently produced the strongest and most reliable improvements overall.
Why high-intensity intervals affect blood vessels differently
The interesting part of this research is not just that intervals worked well, but why they may work differently from standard cardio.
During interval training, blood flow repeatedly surges and recovers as intensity rises and falls. That creates large bursts of shear stress, essentially friction against the walls of blood vessels. While that might sound negative, it’s actually one of the key signals that tells blood vessels to adapt, become more flexible, and produce more nitric oxide.
Nitric oxide is one of the body’s most important compounds for vascular health. It helps blood vessels relax, improves circulation, lowers vascular resistance, and supports healthier blood pressure regulation.
Researchers found that high-intensity interval exercise improved endothelial function significantly more than moderate continuous cardio. Resistance training alone showed far less consistent benefit, though the authors noted many of those studies were shorter and may not have lasted long enough to show meaningful vascular changes.
What this means for your workout routine
This study does not mean everyone needs to sprint through brutal workouts six days a week. The researchers themselves point out that moderate cardio still meaningfully improved vascular health compared to doing nothing.
But it does challenge the idea that all cardio produces identical effects inside the body.
A few intentional high-intensity intervals may create a stronger signal for cardiovascular adaptation than simply staying in the same comfortable zone for 45 minutes straight. That could look like cycling hard for one minute followed by recovery periods, brisk uphill walking intervals, rowing intervals, or alternating faster and slower jogging efforts.
And while headlines often reduce heart health to cholesterol numbers or resting heart rate, vascular function may be one of the earliest places where exercise changes the trajectory of long-term disease risk. Your arteries respond to how you move long before symptoms appear.
The takeaway
One of the most compelling ideas in this study is that blood vessels seem to thrive on variation, not just volume. Periods of challenge followed by recovery appear to send a stronger message to the cardiovascular system than steady effort alone.
That doesn’t mean longer walks, bike rides, or moderate cardio suddenly stop mattering. They absolutely do. But if your current routine has become entirely predictable, your arteries may benefit from the brief moments when your body has to rapidly adjust, recover, and become more resilient in real time.