Anatomy of the foot – or where to start?
The human foot is a unique structure in the animal world. The bipedal way of walking has triggered a series of adaptations that have led to its current shape. The characteristics that distinguish us from the great apes are the long toe and the lack of the ability to counter it. The presence of a longitudinal arch in the foot is also unique to humans. Despite these differences, humans and great apes share similarities, such as walking on the whole foot and the stiffness of the midfoot. The unique features of the human foot, including the springing of the longitudinal arch and short toes, are likely adaptations for long-distance running [1].
Fig. 1: The human and chimpanzee foot. (A) Bone skeleton (B) kinematics of the foot during the push-off phase – the longitudinal arch of the human foot stiffens the foot, allowing the heel and metatarsal to be pulled off the ground simultaneously during gait [1].
Heel walk, forefoot run
A characteristic feature of human gait is the initiation of foot contact with the ground by the heel. The heel bone has a structure that allows it to dissipate forces during impact. The human characteristic element is the large developed heel cusp and the lateral process of the heel cusp – it is believed that this bony protrusion increases the surface area of the heel to aid force dissipation during gait. In addition, underneath the heel there is fatty tissue with a characteristic lobular structure, which is responsible for even better cushioning. Walking from the heel is more energetically beneficial for bipedal gait. However, when running, the forces acting on the foot during ground contact are approximately two to four times higher than those experienced when walking barefoot [2]. This can be noticed by anyone who runs without shoes – automatically the feet start to land on the mid or forefoot, as the heels simply start to hurt.
The foot – our shock absorber
The foot, adapting to bipedal locomotion, had to undergo a number of adaptations. Loose bones had to be stiffened with ligaments and appropriate muscle activation. Effective rolling of the foot requires stiffening of the tarsal joints (between the heel bone and the metatarsal). This is achieved by the longitudinal arch, which is made up of 9 metatarsal bones: the calcaneus, ankle, scaphoid, glenoid, and the first 3 metatarsal bones. It is stabilised by ligaments, muscles and, most superficially, by the soleus tendon. This complex is located from the heel to the base of the toes. Due to this course, there is tension on the soleus tendon when the toe is pushed upwards, which is called the reel-to-reel mechanism [3].
Reel mechanism
The extension of the toe causes tissue tension that draws the heel towards the heads of the metatarsal bones, effectively raising the longitudinal arch and stiffening the metatarsal during the push-off phase. This effect described by Hicks is compared to a reel, because the soleus tendon wraps around the first head of the metatarsal bone precisely like the drum of a reel. This tension pulls on the heel bone, shortens the height of the arch and thus stiffens the foot so that an effective strike is possible.
Trigger mechanism
In addition to the recoil effect, the spring mechanism has also been described in the literature. During contact between the heel and the ground, a so-called pre-charge takes place by creating tension in the soleus and soft tissues. This tension is maintained and, through it, the so-called energy charging phase begins, as the tibia moves forward.
The activation of the so-called recoil effect (trigger mechanism) occurs when the heel pulls off the ground and the forefoot kicks out. This process of compression and recoil has been termed the ‘spring mechanism’ of the foot. It allows energy to be stored and then released during each foot contact, which can reduce energy expenditure during gait [4].
What do the cushioning mechanisms of the foot have to do with minimalist shoes?
The cushioning mechanisms described above are able to activate primarily when we are barefoot. Nothing then restricts the mobility and function of the foot. However, when shoes with a rigid sole are worn, the muscular and ligamentous structures are no longer responsible for carrying the load and are replaced by the cushioning materials of the footwear. In addition, we are also most often confronted with tapered toes in classic shoes, which restricts the correct positioning of the toe and thus its optimal function (and let us note how important its role is in the reel mechanism). The compressed toe at the front of the shoe completely prevents the involvement of the short muscles of the foot, which are responsible for shock absorption. As a consequence of years of stiffening the foot, its muscles weaken and stretch – which can lead to pain, foot defects (e.g. flat foot) or the occurrence of neuralgia.
So what happens in minimalist shoes? By design, they imitate barefoot walking as closely as possible. So they have a very thin and flexible sole, a wide, toe-fitting front and no cushioning. If we have been walking in such shoes since birth, our feet have the opportunity to train their muscles every day, they do not atrophy and they control the alignment of the foot independently. However, when we have walked for many years in ‘classic’ shoes with a hard, cushioned sole – the transition to minimalist shoes can involve a risk of injury. A rapid transfer without strengthening, the foot, stretching contracted muscles and adapting the sole to new stimuli can end in injury and frustration. When buying your first pair of minimalist shoes, it is worth being patient, as the destructive effects of previously worn shoes can take time and work to restore the foot’s natural cushioning function. But it is worth the time, as it is an investment in all our joints.
Barefoot cushioning in barefoot shoes
If we make the effort to train the foot so that the muscles are able to maintain its stability, this brings a number of benefits – reversing the negative effects of wearing compressive and rigid footwear. Strengthening the muscles of the foot corrects faulty alignment (e.g. heel valgus and lowering of the longitudinal arch), which automatically leads to correct knee alignment (in the case of a flat foot, valgus knees may also co-occur). Misalignment of the knees can cause them to wear out more quickly, overloading the muscles, but it also affects the hip joints – generating overloading in them. Some of the existing disorders in the body have their root cause in the feet, and correcting their alignment gives an improvement in the functioning of the upper levels.
From the point of view of cushioning and the sole – the heel, or any other position of the heel higher than the toes, automatically changes the arrangement of the whole body, the curvature of the spine and the position of the centre of gravity. It shifts forward, causing an abnormal distribution of muscle tone (the muscular balance between the front of the body and the back is disturbed). Walking barefoot or on flat soles ensures neutral alignment of the pelvis and the entire spine.
The aspect of the stimuli coming from the sole of the foot itself is also important – the nerve endings of nerves from all over the body are located there. Alternating pressure on the various reflex points on the foot can have a beneficial effect on our entire body, including our internal organs.
Can minimalist shoes be used occasionally?
There are times when, for a variety of reasons, we do not want or cannot give up our classic shoes with a rigid sole and cushioning. This does not mean that it is not worth taking the time to even occasionally go barefoot or use shoes that imitate this. Runners can significantly improve their running technique and performance if they introduce barefoot running or minimalist shoes into their training units. Similarly, those who train team games by also working on foot strengthening reduce the risk of injury, e.g. ankle sprains [5].
How do you start walking in barefoot shoes?
The transition to walking in minimalist shoes involves some work (correcting a foot defect, stretching contracted muscles, strengthening weakened ones). A transfer done abruptly can involve the risk of injury, especially if you have used footwear that weakens and deforms the foot for many years. However, the benefits for the whole body are so great that the topic is worth considering. If someone is struggling with problems, defects or pain in the foot or higher joints, it is worth consulting a physiotherapist who works with the foot – he or she will be able to examine, assess deformities, loosen up strained tissues and select exercises so that walking in minimalist shoes is a pleasure and has beneficial effects on the entire body.
Literature:
1. Holowka N. B., Lieberman D. E., Rethinking the evolution of the human foot: insights from experimental research, Journal of Experimental Biology 2018, 221.
2. Gill C. M., Taneja A. K., Bredella M. A., Torriani M., DeSilva J.M., Osteogenic relationship between the lateral plantar process and the peroneal tubercle in the human calcaneus, J Anat. 2014, 224(2), s. 173–179.
3. Welte L., Kelly L. A., Lichtwark G. A., Rainbow M. J., Influence of the windlass mechanism on arch-spring mechanics during dynamic foot arch deformation, Royal Society, 2018.
4. Kelly L. A., Lichtwark G., Cresswell A. G., Active regulation of longitudinal arch compression and recoil during walking and running, J R Soc Interface. 2015, 12(102).
5. Hryvniak D., Dicharry J., Wilder R., Barefoot running survey: Evidence from the field, Journal of Sport and Health Science 2014, 3, s. 131-136.
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