When the tiny blood vessels in muscles don't respond well to insulin, it's linked to being overweight, having insulin resistance, and getting older — and this might actually happen before the muscle cells themselves become resistant to insulin.

In rats, eating a diet that's a bit high in fat or salt messes up blood vessel function in muscles before the muscle cells themselves become resistant to insulin — and that blood vessel problem alone can slow down how much sugar the muscles take in.

In male rats, insulin helps blood flow to leg muscles pretty quickly—but only if they're eating regular food. If they're on a high-fat diet, insulin doesn't do this job well anymore.

When mice have a broken insulin signal in their blood vessel lining, their muscles don’t get enough sugar—even if the muscle cells themselves work fine—because the blood flow to the muscles drops.

People with mild high blood pressure who have trouble using insulin well also tend to have muscles that don’t take in sugar properly and don’t get as much blood flow — suggesting their metabolism and blood vessels might be struggling together.

In male rats, a hormone called GIP can block insulin’s ability to increase blood flow to leg muscles, even when insulin levels stay the same — suggesting GIP directly interferes with how insulin works in the blood vessels of muscle.