Some common sneaker or elderly walking shoes will have a feature-with toe tilt. This kind of shoes will make it easier to walk, but scientists at Harvard University noticed that such a toe design does not conform to the evolution of human feet. In a recent study published in Scientific Reports, they said that the shoes make people feel light to walk or transfer the force to other parts of the foot, and this change may be the cause of some foot diseases.

Suspicious Lightness

According to archaeological evidence, shoes entered human society about 40000 years ago. By now, shoes have evolved into various styles. A pair of excellent shoes can alleviate the impact of walking and exercise on the feet and knees, prevent foot skin and bone damage, and play a proper warm effect. In addition, some shoes will be through a special sole design, people walk very light or very comfortable soles.

When walking, especially when exercising, the effects of shoes on the feet and body are more complex than they seem. Professor Emeritus of Biomechanics at the University of Calgary, BennoNigg has long studied the effects of sneaker on the human body during exercise. He found that compared to wearing some specially designed shoes to achieve the effect of shock absorption and cushioning, runners intuitively choose the shoes that they think are comfortable and the running style that suits them, and the damage to their feet is small.

Daniel E.Lieberman (DanielE.Lieberman), a Harvard anthropologist who has long run marathons, is also interested in the effects of barefoot and footwear on your feet during running. In 2010 and 2019, his research team published two separate studies in Nature on barefoot running. They found that running barefoot produced better cushioning than running in shoes. Although walking and running with light running can cause thick cocoons to grow on the feet, this does not reduce the sensitivity of the feet.

sneaker with toe tilt. (Photo source: Sichtingetal, 2020)

Recently, Lieberman and his former doctoral student Freddie Sichtin (FreddySichting, currently a professor of human kinesiology at Chemnitz University of Technology in Germany) studied the effects of a characteristic that Benno Nig ignored but is common in sneaker-shoe tip-on feet. Shoes with toe tilt are very common in life, such as some common sneaker or elderly walking shoes. In the design, the toe of these shoes is raised at a certain angle, which makes it easier for people to walk or run in these shoes. And this kind of shoes are often recommend by some businesses as suitable for running, climbing and travel and other sports. Recently, Lieberman and Sichting published a study in Scientific Reports, saying that from the perspective of human evolution, this feeling of ease may not be simple.

The state of the foot when walking

The metatarsophalangeal joint (metatarsophalangealjoints,MTP) plays a key role in human upright walking. It connects the toes of the person to the rest of the foot, making the feet more stable and faster in walking and running. A study published in 1954 concluded that when the metatarsophalangeal joint flexes upward, the plantar aponeurosis (plantaraponeurosis) that connects the toe bone to the calcaneus becomes tighter, creating an upward force to counteract some of the pressure on the longitudinal arch of the foot, thus making the feet more stable as they move forward.

When people wear a pair of sneaker with the tips of the shoes tilted upward, the metatarsophalangeal joint will rise upward along the arc of the toe, which will produce a similar effect. The feeling of walking more lightly is caused by the reduction of pressure on the longitudinal arch of the foot. Sichting said, "From an evolutionary chemistry point of view, it's still a very short-term phenomenon for humans to wear these modern shoes with arch support, cushioning and other support." In the process of evolution, people's feet are mainly suitable for walking on parallel ground, and this way of walking with toes tilted upward may be harmful.

The plantar aponeurosis tightens when wearing shoes with a raised toe (Image: Sichtingetal, 2020)

In the new study, Lieberman and Sitchin used a small experiment to test the effects of such shoes on people's feet while walking. They asked 13 participants to go barefoot or wear sandals with toe tilt of 10 °, 20 °, 30 ° and 40 °, respectively. The angle of the toe bend and the hardness of the sole mimic the shoes available on the market. When the participants walked on the treadmill, they recorded the force they needed to walk and the changes in the joints of the feet through devices such as pressure plates and infrared instruments.

The researchers found that in the initial stage of walking, that is, in the process of exerting force with the foot, the tip of the shoe will significantly affect the bending range of the metatarsophalangeal joint and limit its range of motion. Compared with the sandals with the smallest (10 °) of barefoot and toe tilt, when the tilt of the shoes increases, the negative work done by the human feet when walking will be significantly reduced. At this time, the movement of the muscles around the metatarsophalangeal joint and the longitudinal arch of the foot is significantly reduced. These muscles need to be active to maintain the balance of these structures and make the feet more stable during walking and running.

Although the changes in the activity of these muscles in the study were only slight, when we wear these shoes and walk thousands of steps a day, as the amount accumulates, the activity of these muscles will be significantly reduced, which will lead to their strength and even loss of function. Lieberman said that this further reduces the tolerance of the foot, which in turn leads to a series of injuries and an increased risk of foot diseases such as plantar fasciitis (plantarfasciitis) when the foot is overused.

Causes of disease

Plantar fasciitis is a common foot disease in runners who exercise heavily or in the elderly. The plantar aponeurosis can develop micro-damage and some small inflammation due to long-term activity. When this condition gradually accumulates, plantar fasciitis can form. At the onset of symptoms, there is often a sharp pain in the soles of the feet. Why long-term wear toe upturned sneaker, suffering from plantar fasciitis risk will increase it?

Lieberman explained, "We think the reason for this is that when people exercise, what they need to rely on the muscles in the foot to do is transferred to the plantar fascia. As the muscles in the foot become weaker, the plantar fascia will need to do more work. However, the plantar fascia has not really evolved this part of the function, so it becomes inflamed." With the accumulation of this process, will further lead to a variety of foot injury, and even the formation of plantar fasciitis.

They also said more research in this direction is needed, given the small sample size of the study. The current study is not enough to confirm that shoe tip tilt is directly related to plantar fasciitis and other foot problems. In addition, they will further study how the toe tilt affects the hardness of the shoe and the effect of the cushion on the feet. Of course, out of caution, we may be able to wear shoes with no toe tilt or small angles, especially for special foot-consuming activities such as running and basketball.