Despite the way our species evolved away from climbing trees to walking on flat ground, some people are still walking around with monkey-like feet. In fact, you may be surprised to learn that about eight percent of the population, or 1 in 13 humans, may have a midtarsal break in their foot characteristic of non-human primates. These are also referred to as prehensile feet.
What is a Midtarsal Break?
The midtarsal break is a medial shift in the center of the pressure trajectory with dorsiflexion of the midtarsal joint (the joint between the talus and the navicular bone as well as the joint between the calcaneus and the cuboid bone), occurring during the gait of an unstable foot, when the body transfers weight from rearfoot to forefoot.
A midtarsal break, also known as floppy feet, tend to occur in people with flatter feet and higher body mass indexes than people with stiffer feet. They also tend to roll their feet more, causing a motion called hyperpronation (they land on the outside of their feet and roll dramatically inward). This allows for the foot to relax its joints and ligaments, creating a midtarsal break.
What are Prehensile Feet?
Prehensile feet are lower limbs that possess prehensility (the ability to grasp like a hand). They are most commonly observed in monkeys. Due to the development of bipedalism in humans, the hands became the focus of prehensility and the feet adjusted to more of a stabilizing role. It may be possible, however, that the foot does not reach its limits of dexterity due to the constant muscle tension needed in stabilizing and balancing the foot to hold up the legs and the rest of the frame.
People with prehensile feet can grasp small objects between their toes, manipulating them as with a hand with the ankle functioning like the wrist. As toes are much shorter than fingers, and since the ball of the foot is so large and obtrusive, grasping does not function as in a normal hand and the foot is not able to hold very large or heavy objects.
Chimpanzee Feet vs. Human Feet
Conventional wisdom has always claimed that the human mid-foot is rigid, which allows for more efficient walking while chimpanzees and other apes have flexible feet better suited to grasping branches as they move through the trees.
Human feet are both rigid and pliable depending on the need. The human foot is a spring arch that should be able to drop and lift with every step. Human legs angle in from the hip to the knee, allowing our feet to fall directly under the pelvis and our pelvic muscles are much stronger, as well, allowing for a stable upright environment.
Chimpanzees are often referred to as knuckle-walkers because they only walk on two legs for short distances due to the differences of our legs and spine. Chimpanzees can’t straighten their legs like humans and they don’t have a lumbar curve, which makes weight bearing and walking more difficult. Chimpanzee legs are also set wide apart and weak pelvic muscles force their whole body to transfer weight from side to side during each step.
Yet, while chimp feet and bodies can’t do what humans can, it doesn’t appear to be a problem if our feet work like chimpanzee feet. In fact, two studies (one from Boston University and the other from Dartmouth) have proven that about eight percent of the population have the mobility of chimpanzee feet, which allows some societies to functionally adapt their feet and calf muscles to allow them to climb trees like chimps do.
While eight percent of the population exhibits a flexible midtarsal break in their feet, people with midtarsal break rarely realize that they have one, as it doesn’t affect their gait.
The Walking Test
So how do you know if your feet might have a midtarsal break? Take a stroll on sand. Here are a couple of tips:
- If you have high arches, you probably have stiff muscles and ligaments, which means that you don’t have a midtarsal break.
- If you have a midtarsal break, the fold in your foot will pinch the sand upward. Look for a small ridge in the upper-mid portion of your footprint.
Talk to Dr. Vikki and Dr. Connie
If you have any questions or concerns about whether or not you have prehensile feet with a midtarsal break, and if there are any unique factors you have to account for regarding your foot health, feel free to book an appointment with Dr. Vikki and Dr. Connie today.