It’s a routine familiar to anyone who has stepped into heels for the night: By the time you’re on your way home, the shoes become too uncomfortable to bear, and they end up in your hands instead of on your feet.

Now, a new study uncovers what causes those heels to be so painful that they just have to come off.

Conducted by researchers at the University of Jyväskylä in Finland, the study found that wearing high heels for extended periods of time entirely changes the mechanics of how women walk. Women who wore heels frequently had shorter, more forceful strides and put more strain on their muscles, caused in part by a shortening of the calf muscle fibers, according to the study.

When walking regularly, the muscles and tendons should work together to allow women to stretch each leg and stride out, Stephen Piazza, associate professor of kinesiology at Penn State U., said.

But as someone walks in high heels, the toe remains pointed downward with the heel up. The tendons are never given the opportunity to stretch out and the calf muscles remain short.

“If you walk all the time with your feet in a plantar flexed position, which is what you have to do in high heels, your muscle fibers are going to become shorter,” Piazza said. “As you’re always pointing your toes and you walk around that way for enough time the muscle learns to adapt, and it’ll become permanent.”

The tendons in the leg also store elastic energy as someone walks and stretches. As those springy tendons are doing their job it actually saves the walker metabolic energy, Piazza said. But when a person wearing high heels does not allow that tendon to stretch it becomes tight and doesn’t have the same capacity for energy storage. Instead, high heel walkers rely almost solely on their muscles, which can cause rapid muscle fatigue.

These tight tendons and shortened muscles can also cause other problems.

“If they become short and tight, they’re not as able to generate as much of contraction. There’s not much room to shorten since they’re already short,” Piazza said. “You can’t generate as much energy with your muscles when you’re walking and that’s bad because you need to generate energy when you walk and you need to be able to push off.”

To conduct the University of Jyväskylä experiment, researchers enlisted nine women who had worn high heels for 40 hours a week for at least two years and 10 women who wore high heels periodically for less than 10 hours a week.

The women were equipped with electrodes to track their muscle activity and various other attributes as they walked. According to the study, not only did strides appear shorter and choppier, and put more strain on the muscles when the women were in high heels, those who wore high heels frequently saw the same effects when walking barefoot.

With research available on the negative effects of high heels, Piazza poses a question.

“If high heels are so bad, why is there no change in usage? The reason is people think they look good in high-heels,” Piazza said. “How far are women willing to go to look good even though they’re doing damage?”

Several Penn State students came to the same general consensus — they’ll continue to wear high heels because they love how they look in them.

“It makes an outfit look better. You have to complete the look with shoes,” sophomore Danielle Weiss said.

And while they agree that high heels can be painful and potentially harmful, they’ll continue to slip their feet into them on a regular basis.

“You may pay for it later, but there’s worse stuff out there than high heels,” junior Lauren Applegate said.