Trouble begins when clots form inside blood vessels without a clear reason. Picture traffic on a busy highway suddenly coming to a complete stop for no apparent cause—that’s similar to what happens when a clot disrupts the normal flow of blood through your veins or arteries. If a clot breaks loose and travels, it can become lodged in the lungs (causing a pulmonary embolism), the brain (leading to a stroke), or the heart (triggering a heart attack), resulting in potentially life-threatening consequences.

So Why Is Sitting Such a Big Deal?

It turns out that sitting for long stretches—whether during a 12-hour Netflix binge, a cross-country flight, or a regular day at a desk job—can cause blood to pool, especially in the lower legs. As blood isn’t moving, it becomes more likely to clot.

As per Dr. Danielle Belardo, a preventive cardiologist, regular movement encourages healthy blood circulation. “Your muscles help push blood through your veins. When they aren’t being used, blood flow slows down—and that’s where the danger begins,” she explains.