What Heel-to-Toe Drop Is, and Why It Matters

When you read about a running shoe's details you'll often see the phrase "heel-to-toe drop" (HTT drop) and a measurement in millimeters. (HTT drop is listed under "differential" here on Zappos.) Just like determining whether you like a narrower or wider shoe, one with more cushioning or less, finding the HTT drop that works best for you can take a little sleuthing. But, experts agree, doing so can help lower your injury risk and make running more enjoyable. Here's what you need to know about HTT drop:

What is heel-to-toe drop?

Heel-to-Toe Drop Explained: The heel-to-toe drop, also known as 'drop' or 'offset,' is the precise millimetric difference between the height of a shoe's heel and its forefoot. For instance, a popular running shoe like the women's Brooks Launch boasts a 10 millimeter heel-to-toe drop. This implies that your heel will be positioned 10 millimeters higher than your forefoot when wearing the shoe. Although 10 millimeters is a common measurement, the range of heel-to-toe drop in running shoes can vary significantly (from 0–14 millimeters), as we'll explore further. This measure plays a critical role in your running posture and overall comfort.

HTT drop is different from stack height, which is the distance between your foot and the ground when you have a shoe on. The two measurements are related, however, as stack height, which is stated for the heel and forefoot, is used to determine the HTT drop.

Why Does HTT Drop Exist?

Running shoes of 50 years ago didn't really have a HTT drop. Almost all shoes were flat or almost flat (and had a low stack height). That started to change during the first running boom of the 1970s, thanks to two related developments: First, a broader cross section of the population, including many previously non-athletic individuals, took up running. Second, in an effort to make running more comfortable for more people, shoe companies developed more cushioned midsoles.

Putting additional cushioning in the heel compared to the forefoot was done to reduce stress on calf muscles and Achilles tendons, says Jonathan Beverly, author of Your Best Stride and former shoe editor for Runner's World.

A HTT drop of 10 to 12 millimeters remained standard until the best-selling book Born to Run helped spark the barefoot running and minimalism movement almost a decade ago. Advocates said that a small or nonexistent drop encourages more natural foot and ankle motion and more evenly distributes running's impact forces.

Although minimalism is no longer a widespread phenomenon, its impact can be seen in many current running shoes. Hoka One One offers a 4-millimeter drop throughout its line. Altra takes things even further, coining the term “zero-drop" to describe the completely flat construction it incorporates into all of its models.

Beverly says that a drop of 8 to 10 millimeters is the new normal (with higher and lower drops also available).

“This range seems to work for a broad range of runners," he says, "particularly for the casual runner who wants her running shoe to be simple and versatile, equally comfortable on the run, in a gym, or at the office."

Does Drop Matter?

What's a runner to make of all this? For starters, know that there's no evidence that a shoe's drop affects overall injury rates. A study published in 2016 in the American Journal of Sports Medicine followed three groups of runners for six months. The shoes they ran in were identical except for having a 0-, 6-, or 10-millimeter drop. About 25 percent of each group suffered a running injury during the study.

That said, a shoe's drop can be important if you have a history of injury to certain sites or some key bodily characteristics.

“Runners with tight calves and an aggressive heel strike should probably stay in a slightly higher-drop shoe, 10 to 12 millimeters," says Abby Douek, a physical therapist and owner of Run Raleigh Physical Therapy and Performance Lab in Raleigh, North Carolina. “Also, runners with Achilles tendonitis may need to briefly go into a higher drop to relieve tension on the tendon.

"Those who naturally run more towards mid- and forefoot can typically be in a 4-millimeter drop without a problem," she continues. "The lower the drop, the more calf flexibility and ankle mobility you need."

Most experts agree that runners with chronic knee issues could benefit from a lower-drop shoe, which will move some impact forces off the knee to the lower leg. But, remember, those impact forces have to go somewhere.

“In general, a shoe with a higher drop will be easier on the lower leg—foot, ankle, Achilles, calf—while directing more stress to the knees and hips," Beverly says. “A lower-drop shoe will typically spare the knees but put more stress on the lower leg."

If you're not seeking a solution to a chronic injury spot, let comfort, not variations of a few millimeters, be your guide when considering drop. Beverly advises picking running shoes that feel like an extension of your feet once you're running in them. What that means in terms of drop will vary greatly from runner to runner, depending not only on injury history, but also speed, foot strike pattern, flexibility, strength, and more.

Know your current shoes' drop when it's time to shop, Douek advises.

“If you're not experiencing any difficulty in your current shoe and just need a new pair, stick to the same drop that you're in," she says. If you decide to try shoes with a lower drop, Douek recommends transitioning slowly, by no more than 2 millimeters at a time.