Are chimpanzees Plantigrades or Digitigrades

BALANCING IS NOT THE NATURALLY PREFERRED WALK IN HUMANS

Ever since I came across the idea of ​​the so-called ball walk, I have been looking for evidence for this theory, as I too initially found the basic idea to be quite logically comprehensible. It is said to be the only natural way of walking. Walking over the heel is a harmful and unhealthy habit that stems from military marching and is caused by wearing poor shoes. However, there is no scientific evidence.

In my workshops, participants who have already dealt with ball walking and are trying to practice it are often relieved when I explain to them why it is probably not the "correct" gait of people and certainly not the only true one acts. Because many beginners have difficulties converting to the ball walk. While (estimated) 95 percent of my test subjects land reflexively over the forefoot when walking barefoot (running) on ​​hard ground, when walking it does not automatically adjust as soon as they move barefoot. This observation made me doubt the theory that the ball walk was the only natural way to walk.

During my in-depth research, I found that the findings on the gait of primitive peoples, the evolution of human movement patterns, biomechanics and child development, repeatedly led me to the opposite, and I did not come across any evidence that really supports the ball gait thesis. Indications that, for example, indigenous peoples go permanently over the ball, could not (until now) be found.


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What is the ball gait anyway?

With the ball of the foot or forefoot walking is meant the touchdown over the forefoot. According to the idea of Ball gang the foot should first touch the outside of the ball of the foot (little toe), then over the inside (big toe joint) and only at the end with the heel. The basic idea of ​​this type of footrest is to use the elastic elements of the arch of the foot and the lower leg as a suspension system, just like when running. This suspension should then put less stress on the joints and bones, since when the heel hits the ground the impulse hits the entire bony system without being dampened.

At first glance, this appears logical, and we will also see that a smoothing of the shock pulse can actually be measured. But does that also mean that the Ball gait is really healthier or prevents damage to the tissues?

Differentiation between running and walking

The most important point right at the beginning: Like many other terrestrial mammals, humans have developed certain movement strategies (gaits) in order to react to the different forces (gravitational force and the resulting ground reaction force) at different speeds of movement. The forces that arise when walking are still quite small and increase with the speed of movement to two to three times the body weight when jogging and ten times when sprinting. Through a movement behavior adapted to the speed, we have the ability to adequately disperse the rising forces.

Switching from walking to running is more efficient relative to the additional muscular effort (Carrier 1984) and also reduces the risk of overloading or injuries. (Lieberman 2010) A changed joint position and a different motor sequence of the limbs leads to a modulation in the myofascial tissues, which compensates for the extra work of the muscles through increased elasticity. (Biewener et al. 1998)

Man has three gaits: walking, running and sprinting. Walking and running are often incorrectly equated, although they are kinetically and kinematically very different. If a horse were to remain in its "step" gait despite increasing speed, it would at some point run the risk of being injured due to increased torque and shock loads. So it has to change its pace. In addition, a change of pace is always associated with the lowest possible energy consumption. A horse's trap is more economical and gentler than a gallop for lower speeds and vice versa for higher speeds.

The flight phase is typical for the sequence of movements when running. Both feet leave the ground at the same time. That is the jump portion of this locomotion. If you jump, you have to fall back towards the ground in accordance with the mass attraction. When we walk, we fall with every step at the moment when the foot sinks back to the ground after being deflected to the maximum forwards. The height of fall is between 0.5 and 2 cm, depending on the walking speed. Most studies indicate an increase in body weight strength when putting on heel (barefoot) of 1.1 times body weight. Compared to running, where we have to do with falling heights of 4 - 20 cm and an increase in weight of two to three times the body weight, so comparatively low. On the one hand, this is due to the low height of fall and, on the other hand, the fact that the standing leg is still in contact with the floor when the foot is raised and the effective mass that falls on the floor is reduced.


Kinematics walking and running

In each running and gait cycle there is a swing leg (no contact with the ground, swings forward) and a supporting leg (contact with the ground). The swing leg swings forwards when walking and swings around the pelvis (hip joint) in order to then come up in front of the body for the next step. From the lowest point, the pendulum is accelerated to the maximum and now moves away from the body.

The kinematics of running (jogging / running) is roughly the same as kicking a scooter. Unlike the scooter, it is a combination of jumping (vertical force development) and pulling (horizontal force development). The knee of the swing leg is raised in front of the body and the foot is pulled in front of the body. From there the foot is pulled back towards the ground and at the same time towards the body and ideally comes into contact with the ground under it. (See illustration) The two optimal contact points of the foot result from these different strategies. For walking in front of the body and for running under the body.


In order to swing the swing leg forward, the foot must be drawn into dorsiflexion, i.e. towards the body, as otherwise it would drag across the ground. If the foot swings past the ground and climbs higher again, it is at this moment the heel that is closest to the ground. In order to be able to put the forefoot on first, it would first have to be tilted downwards. For the Ball gait an additional movement action is required.

If you touch down with the heel, the ground reaction force applied at an angle to the calcaneus (heel bone), together with the gravitational force that pulls the forefoot to the ground via the calcaneus as a tipping point, causes a quasi-automatic plantar flexion of the foot without energetic expenditure. (Earls 2016) This mechanism is known as the calcaneus seesaw.



Due to the kinetic chains of the myofascial tissue (Myers 2004), the calcaneus rocker leads to increased tension on the lower leg, which as a lever with the ankle as the pivot point also lever the knee forward. If the knee is in front, the pelvis also follows it via the thigh lever and pushes the body's center of gravity forward. This process is called an inverted pendulum, in which the ankle is the pivot point and the pelvis is the mass point. (Cavagna 1977) The kinetic levers and the pendulum principle make walking so efficient.

Just as a person uses the pendulum as a basic physical principle of oscillation theory when walking, he uses a different one when running (jogging / running). Running is like jumping from one leg to the other. So that one does not have to generate too much force from the muscles with every jump, man developed a spring-mass system with special elastic structures in the lower extremities over millions of years. These spring elements can be tensioned on impact and the then stored elastic energy can be released again as recoil. (Cavagna 1977)

With a trained barefoot running technique, the human Achilles tendon can absorb around 35%, the transverse and longitudinal arches around 17% of the energy. (Ker et al. 1987) If you first touch the forefoot from the walking movement, then, as described above, the pull on the lower leg, which is caused by the plantar flexion, is overridden. The propulsion forwards must take place through active muscle contractions.

As the study by Cunningham et al. (2009) shows that walking over the ball of the foot requires up to 53% more energy. In particular, the hamstring muscles (rear thigh muscles) and triceps surae (calf muscles) are excessively challenged (up to 128% more). There is a simple explanation for this: If you put your foot first on the ball of the foot in front of the body and then with the heel, this is a movement that is opposite to the direction of the gait or is directed backwards. There is no tension on the lower leg lever that pulls the knee forward. So the pool stays in place. That's why you're at Ball gait has the feeling of not getting out of place and can only take very small steps.
The strength for locomotion must then come from the muscles, and the kinematic pattern changes from pendulum motion to horizontal and vertical pulling motion, for which mainly calf and hamstring muscles have to be activated concentrically.

Raichlen and Webber (2016) found a further energetic advantage: Landing on the heel increases the effective length of the lower extremities by more than 20% than when sitting on the ball of the foot. This results in a more effective lever arm for translating the pelvis over the ankle. (Raichlen & Webber 2016) Unfortunately, the energetic aspect has not yet been investigated in more detail, so it has to remain a hypothesis for the time being. Further research would be needed here.


anatomy

"Nothing in biology makes sense, except in the light of evolution." (Theodosius Dobzhansky)

Compared to other great apes and arboreal ape species, which primarily climb trees, it is noticeable that the more often and closer a species of monkey is to the ground, the larger its calcaneus (heel bone) becomes in relation to its body size. (Morton 1922) In all ape species, with the exception of the great apes, the calcaneus hovers in the air. (Gebo 1992) When these species walk on the ground, they only do so on the forefoot and toe area. Bonobos, chimpanzees and gorillas are pure heelshoots when it comes to their hind legs. Your calcaneus has a shape similar to that of humans. The massive form of the calcaneus in apes and humans speaks for its load-bearing and absorbent functionality. In the thesis of Ball gangthe heel should only land on the ground after the ball of the foot.

That is, it would only serve as a support point for walking and standing. One could assume that the calcaneus, in its function as a pulley, has to be so massive that it can withstand the enormous tensile forces between the Achilles and the plantar fascia when running. The example of a kangoroo, in which similar forces act on the Achilles tendon, shows, however, that the deflection is also possible via a very small calcaneus. (Alexander, 1988) The sole existence as a guide pulley does not explain its size. The internal arch-like structure of the calcaneus is very similar to that of the femoral neck. Many small longitudinally and transversely tensioned tissues give it enormous resistance to vertically applied forces, which mainly occur when the person steps with his heel on the ground and then puts his body weight on the foot. This structure would not be needed as a pulley.

In addition, people have a lot of building fat, especially under their heel bone, which is well suited for an initial shock absorption. (Aerts et al 1995) In the case of the African Hadza, Musiba et al. 1997 saw a much more pronounced heel.

The Neanderthals had a longer calcaneus. He was an even better long-distance walker than the human. (Raichlen 2010) The length of the heel bone brought a longer lever arm to the load point of the ankle. This enabled him to lever his body's center of gravity forward more effectively with the plantar flexion.


evolution

From an evolutionary point of view, energy is one of the most important, if not the most important, selection factors. Most of the time, the daily struggle for survival in nature is about getting energy in the form of food or using little energy or being able to store it well. Since humans as hunters and gatherers, probably as a result of global climate change, had to cover ever greater distances in the course of evolution in order to get enough food, those individuals with the more efficient locomotion strategy were superior, were able to survive longer and reproduce more successfully. (Bramble et al. 2004, Zachos et al. 2001)

Assuming that hunters and gatherers cover about 10–30 km a day, it is very unlikely that they did so in a way that was much less economical for them. (Marlowe 2010)
If we assume a male hunter-gatherer who is 25 years old and weighs 70 kg, he has to work up around 1800 kcal at a relaxed pace of 3.5 h / km for 15 km in order to get enough food at all . Calculated over a week, it is then 12,600 kcal. Let us assume that he is trained in Ball gait and consumes not 53% but only 30% more energy through the other footrest. He would need about 3800 kcal more for the same workload. In times of strong selection pressure and the struggle for resources, that could have cost him his life.

Based on this fact, it can be assumed that the Ball gait is not the preferred gait of Homo sapiens. In the course of evolution, this strategy could only have prevailed in favor of a much more relevant factor than energy. Our cognitive abilities could be such. Since the growth of the brains of the first hominids only emerged from the development of the upright gait, this is at least questionable. (Forssberg, 1992)


Primitive peoples mostly walk on heels

Science agrees that Central Africa is the starting point of human evolution. One of the oldest hominid footprints is the Laetoli imprint found in Tanzania. (Bennett 2009) This was very likely left in a volcanic ash field by one of our ancestors, Australopithecus aferensis, about 3.5 million years ago. The special thing about the ridge is that it has a deeper depression towards the back of the heel area, which can only have been created by the initial attachment of the heel. Raichlen et al. (2007) found that the walking motion of the being responsible for these footprints is very similar to that of modern humans and Musiba et al. (1997) and Nicol et al. (1988) observe a great correspondence between this Laetoli imprint and those of the Tanzanian native people of the Hadza and the Peruvian Indians.

The studies by Kristiaan D’Août (2009) also show through foot pressure measurements and observations of the gait of 70 habitual Indian barefooters that they too put their feet on the heel first. Morton showed the same picture when measuring gait patterns of natives of Central Africa in 1935.

In 1905 Hoffman found no other foot posture when researching 180 pygmies and Filipinos living barefoot, and Wells did not observe any different gait in 74 Bantu people and 24 Bushmen in 1931. The latter even found that these African peoples have a calcaneus that is 3% longer on average than Europeans.

The Australian Aborigenies and individual Amazon peoples are said to Ball gait practice. Another picture is found on video material from 1950.


Ball walk in primitive peoples

The video shows three indigenous peoples (1. Hadza People, Tanzania, 2. Amazonas people, 3. Aborigines, Australia) who, according to the authors, have not yet come into contact with our western culture, or only peripherally. All show a primary heel gait. Every now and then, the forefoot comes first on the ground, probably as a lunge or to compensate for unevenness in the ground. You can also see that the movements, especially the dorsiflexion, are usually quite small and the gait of these people appears light and soft. This is of course no empirical scientific evidence, but rather shows the opposite of the ball walk thesis.



The audible impact

Anyone who sticks their fingers in their ears and then walks a few meters barefoot over their heels will immediately hear the impact. If you then touch down with the ball of the foot first, it becomes quiet. This phenomenon is the argument for the ball walkers to declare the essay on the heel as wrong.However, it is questionable whether the acoustic perception in the ear is really an indication of the harmfulness of this way of walking. Just the fact that I hear something doesn't say much.

Anyone who thinks audible bumps are dangerous should cover their ears the next time they eat a carrot or biscuit. Despite the enormous amount of noise, very few people get osteoarthritis in the temporomandibular joint and nobody starts to eat anything but liquid food for fear of overload.

The impact is audible above all because there is a more or less direct sound conduction in the body from the foot to the head, from the heel via the reverberant structures. In acoustics, this is called structure-borne noise. Put simply, hard, high-density materials can transmit sound better than soft and flexible ones. You know that z. E.g. from a heating system in an apartment building: if you knock on a heating pipe in the basement with an equally hard object (e.g. pliers), you will most likely hear the sound signal just as loud, if not louder, on the fourth floor.
Two factors are “to blame” for this: the reverberant material properties and the resonance chambers of the metal pipes. This system works like a large flute that starts to vibrate. The propagation of sound in solid bodies even creates additional vibrations, the so-called transverse waves, which do not exist in the propagation of sound through the air (longitudinal waves). This additional vibration can amplify the sound when a body starts to resonate. Everyone has probably already experienced how the barely perceptible sound of a tuning fork suddenly becomes clearly audible as soon as it is placed on a wooden table or when we hold it to the top of our skull. Our skull is ideal for making structure-borne sound audible. The skull bones themselves can vibrate well. In addition, there are the sinus cavities (frontal sinus, maxillary sinus, sphenoid sinus and ethmoid sinus), which, like a wind instrument, can make the air they contain vibrate.

The conduction of a sound event that is generated by placing the heel on a hard surface works in a similar way. Our rather reverberant bones can pass the signal on quite directly, and the sound is made clearly audible in the skull area. But there are certainly many sound-absorbing structures such as joints, intervertebral discs, organs and myofascial tissue between the heel and inner ear.

The mere fact that the impact is audible does not mean that it has to be harmful to the body in some way, not even if, as in the case of walking, it is a highly repetitive sequence of movements in humans. In addition, a quiet heel attachment can be learned. The impact that can be heard even without the ears closed is usually the result of steps that are too large with straight knees and a contact point in the heel area that is too far back. With the appropriate practice, however, you can also move quietly barefoot on hard surfaces.


Application of the "ball walk"

There are also a number of natural applications for the digitigrade foot posture (forefoot touches down first).

  1. increased height of fall
    If you walk at a moderate speed, the heel is raised a maximum of 2 cm. If the height of fall increases, for example by jumping slightly on the spot, the impulse is used reflexively for damping by including the elastic elements of the arch of the foot and the Achilles tendon. This also applies to climbing stairs and moving sideways.
  2. unstable movement
    Slow crawling is hardly possible with a plantigrader foot position (heel touches down first). Due to the small footprint of the heel, one becomes unstable and threatens to fall over. Walking with a plantigrade footrest therefore requires a certain dynamic and speed so that the lateral centrifugal forces, similar to cycling, can apply to stabilize the body.
  1. bent knee
    If the knee has to be bent or raised more for the required movement (e.g. climbing stairs), we usually use digitigrad. Possible reasons for this are, first, that the inverted pendulum system no longer works and we have to push ourselves upwards as the thigh muscles increase. And second, that dorsiflexion of the foot is caused by the increased tension in the posterior kinetic chain of the leg, the superficial backline. (Myers, 2004) is prevented by the angled posture. As a result, with the knee bent, the foot can hardly be drawn in.
  1. Foot as a tactile organ
    Most of the mechano and chemoreceptors in the skin are in the toe area of ​​the foot, similar to our fingertips. (Laube, 2009) If we are dealing with a surface that is difficult to assess and want to check its condition, we usually use the front foot for this. Feeling forward with the heel would be mechanically difficult, as we would bring our body weight directly onto the front foot using the lever function or would have to bend the knee of the supporting leg. If we use the forefoot, the center of gravity can stay above the supporting leg and we can feel before the foot is loaded.

However, it is a fallacy that the foot can better adapt to the ground with a digitigrade posture.
In fact, the opposite is more the case. The array of metatarsal and cubic bones in connection with the lower ankle joint (calcaneocuboid and calcaneotarsal joint) leads to a compression of the bone structure when the forefoot is attached and, as a result, to a stiffening of the arch of the foot, which is required above all for running, to absorb energy. (Earls 2016) If the foot touches the heel first, the position of the calcaneotarsal joint causes the talus to incline medially, which leads to an opening of the midfoot bones over two further steps. (Earls 2016) The result is a soft, adaptable forefoot that only stiffens under the weight of the body. This can be tested by placing one foot slightly in front of the body on the heel and letting the forefoot “splash” on the floor. This splashing is nothing other than the open joint position of the foot bones and is not possible with a digitigrade position (with the ball of the foot first).

The scream reflex

The so-called walking reflex is part of the second examination in newborns (U2). The child is held under the arms, above the floor. The toes make contact with the ground, the foot hangs down. As soon as one foot touches the ground, the other leg is drawn in. This alternating leg movement is reminiscent of a walking movement.

However, unborn babies already have the reflex from the first trimester of pregnancy. This enables them to move in the uterus on the one hand (Forssberg, 1986) on the other hand, the movements support neural and muscular growth. (Adolph et al. 2013) About two months after the birth, this reflex disappears again. (Peiper, 1996) So it is more of a prenatal reflex than the first stage of development of walking.

Even if the newborn's toes touch the ground, it is unlikely that they will relate to an adult's footplate. Children learn to walk over the years and in many stages of development (hyperextending, rolling, sealing, crawling, squatting, standing, etc.). It seems logical that a child with untrained neuromuscular connections and untrained foot muscles, held by the arms and first touched the floor with the toes, in its first few weeks. Even an adult would not try to make initial contact with the ground from this position, heel first.


The childlike gait

A widespread argument is that toddlers are naturally predisposed walkers and that their development is disturbed by imitating false role models and wearing bad shoes. Children's anatomy is very different from that of an adult. Only around the age of 15 do the values ​​for balance, motor skills and muscular strength equal those of an adult. (Malina et al. 2004)

Most children start taking their first steps around the age of one. They start with a forefoot strategy and then switch more and more to heel attachment over the course of three years.

Three important factors make it anatomically impossible for an adult to walk at this age.

  1. Human children are born with a C-shaped spine.
    This saves space in the womb and the children get better through the birth canal. The familiar double S-shape of an adult only develops through the movement patterns of the newborn. The overstretching of the neck and the lower back are largely responsible for the characteristics of the two lordoses in the spine. Due to the still existing C-shape, the center of gravity of the child when standing and walking is further forward than that of a healthy adult. This leads to an increased tendency to fall, which in turn can be better absorbed by the forefoot.
  1. The ratio of the width of the pelvis to the span of the ankle on the Frontal plane.
    The legs of a one-year-old child are far out. If the child stands on both legs, the supporting area under the body's center of gravity is 70% of the width of the pelvis. With increasing age, the feet come down below the center of the body and at the age of 3.5 the area is only 45% of the width of the pelvis. (Sutherland et al., 1980) So children initially use the broad and more stable leg position and, with advanced motor skills, reduce it further and further towards the center of the body up to the age of seven.
    The wide-legged position requires a forefoot attachment, as a heel attachment would lever the pelvis too far forward and the child would become too unstable. The ball attachment makes it possible that the foot can stay close to the body's center of gravity under load.
  1. The length ratio of the upper body and head to the lower extremities.
    Newborns have shorter legs in relation to their overall height. In an adult, the pelvis is approximately half the total length. In a newborn, the trunk and head make up more than 65%. The lower extremities of a two-year-old child are only 40% of their body length. (Timiras 1972). In the first few years of a child's life, the head in particular has a much larger share of the total body size than in an adult. As the head, trunk and lower limbs grow at different speeds, the proportions become relative in the course of development. From birth to adulthood, the size of the head doubles. However, those of the torso and legs triple (Abernethy et al. 2013)
    The center of gravity of small children is thus further in the torso (above the pelvis), which means that they are less able to oppose the force of gravity due to the "poor" lever and there is an increased tendency to fall. Another sign that children have to cope with a high level of instability in their locomotion development and therefore use the more stable forefoot attachment. The shorter legs mean that children have to change their pace faster if they want to increase their speed. The transition speed from walking to running is much slower than that of an adult. Therefore, you often see them running (running). In doing so, they also land reflexively on the forefoot.


discussion

At first it seems sensible to say goodbye to the terminology of the distinctive gaits of the ball of the foot and heel gait. It's not about walking, it's about the fact that we can use our feet in different ways while walking. A dogmatic restriction to one of the two possibilities does not seem sensible. Both have their application and the body usually decides itself reflexively which one to use.

In view of the results listed, the strategy of the dynamic, economical, plantigrade footrest seems to be the preferred, if not the only possible one for humans. People probably use the digitigrade strategy primarily in cases of instability, insecurity, uneven floors, ascents (stairs), and increased height of fall, and then put their body stability before efficiency.

However, we must also be aware that in the course of evolution, neither the gait pattern nor the anatomy of Homo sapiens have been adapted to either asphalt inner cities or lush forest floors. The cradle of mankind is in Central East Africa, today's Tanzania. The soils there mostly consist of sandy loam. Walking barefoot on rock-hard surfaces requires an experienced footing, which is often disturbed by years of wearing shoes. There is nothing wrong with making the floor a little softer again by lacing a bit of rubber or other cushioning under the soles of your feet in the form of simple sandals or barefoot shoes. To retrain your gait to the so-called ball gait, I think it is extremely tedious and unnecessary. Many people often fall back on the heel strike when attempting re-education. It does not seem to be a natural reflex that sets in as soon as you take off your shoes and socks and go barefoot. According to my own observations, however, people end up immediately on the forefoot even if they only walk barefoot on hard ground for a few meters (jog / run). This is purely reflective behavior that does not require any explicit instruction. In my work with runners, therefore, it is seldom about the footrest, as it adjusts automatically as soon as the supporting footwear is removed. However, most of them practice the ball gait over weeks or months. The justification that a change takes so long because you went wrong for many years is more of a further indication for me that this is not really a natural movement. And yet there are people who feel more comfortable with this strategy, which in my opinion does not speak against it.

Whether a consistently executed Ball gait can have negative consequences, is beyond my knowledge, as there are no studies on this. In my own, non-empirical observation, it is noticeable that experienced ball walkers often have an increased tone of the calf and foot muscles, tend to have hollow feet and the plantar pressure image when standing shows a primary load on the feet in the ball area, which can lead to symptoms of overload.

To reduce your foot in a certain way or even to force yourself to sit down in a certain way is simply wrong. The foot or the sensorimotor system reacts reflexively to different surfaces or conditions just as differently and usually exactly "correctly". The basic requirement, however, is that you go barefoot for this. Only then can a body-appropriate reaction take place. If you do not focus on consciously controlling the footrest, you will find that both the forefoot and the heel are "used". Therefore, the following always applies in this context: Trust the foot and let it do it.