Postural control requires constant and subconscious postural sway to manage balance and achieve postural stability. These movements of regulation are based in particular on cutaneous plantar information. The foot constitutes a functional whole that participates in the mechanisms of postural control and regulation.
It represents the direct interface between the body and the ground during quiet standing, and plantar cutaneous information contributes to postural control. Upright balance mechanically depends on the gravitational torque produced by the forces of gravity and reaction of the ground. In this context, the foot behaves like a sensory system for postural regulation whose objective is to maintain a state of stability within a changing and constraining environment.
There is a relation between balance improvement and the facilitation of sensory feedback related to the activation of the plantar cutaneous mechanoreceptors. From a clinical point of view, the application of additional tactile cues may have therapeutic benefits in relation to fall prevention, or to improve specific types of chronic pain.
There are a lot more studies on the benefits of proprioception improving insoles on older patient populations or people suffering from disease than on healthy adults or athletes. Times are changing though, and a 2016 study published in the Journal of Biomechanics tested the effect of vibratory proprioception and balance improving insoles on the agility of athletes. It found that athletes wearing insoles could complete the agility task more quickly than those not wearing the insoles. While our proprioceptive insoles do not vibrate to the physical touch, they do emit frequency which stimulates the mechanoreceptors in the skin of the foot in the same way vibration would. They improve many factors contributing to sports performance: joint stability, reaction time, movement efficiency, speed, etc.
Miranda, D.L. et al (2016). Sensory enhancing insoles improve athletic performance during a hexagonal agility task. Journal of Biomechanics, 49 (7), pp. 1058-1063. Doi: 10.1016/j.jbiomech.2016.02.022.
Hyperpronation of the feet is very common. Due to weakened arches the foot collapses inwards. Over pronation can affect the areas around the foot, but a recent study has shown that it also affects muscle function and activation.
Researches showed that hyperpronation of the feet can change the timing and intensity of lumbopelvic muscle activation and may predispose people to develop secondary dysfunctions.
Since altered muscular control of the lumbopelvic region is one of the main risk factors for the development of low back pain and dysfunction, this article helps link hyperpronation to back pain.
Yazdani, F. et al. 2019. Foot hyperpronation alters lumbopelvic muscle function during the stance phase of gait. Gait & Posture, 74, pp. 102-107. doi: https://doi.org/10.1016/j.gaitpost.2019.08.022
Fibromyalgia is a chronic pain syndrome. Patients with fibromyalgia also frequently suffer from balance impairment. Scientists found that adding 0.8 mm of additional thickness under the great toe improves body balance in patients with fibromyalgia. This is because there is an increased distribution of cutaneous afferents in the toes compared to other parts of the foot like the heel. Targeting this specific spot on the foot can greatly improve proprioceptive information going to the brain.
Viseux, F.J.F. et al. (2020). Effect of sensory stimulation applied under the great toe on postural ability in patients with fibromyalgia. Sensory & Motor Research, 37, doi: https://doi.org/10.1080/08990220.2020.1765767
Our feet are our point of contact with the ground. They allow us to sense and interact with our environment. Muscle spindles and mechanoreceptors in the foot send information to the brain about postural sway, balance, and gait. To understand more about the different types of somatosensory feedback coming from the feet, check out this article by Frederic J.F. Viseux. It goes into great detail describing the different ways the feet can capture information and send it to the brain. It’s a great resource for explaining the role feet play for good posture.
Viseux, F.J.J. (2020). The sensory role of the sole of the foot: Review and update on clinical perspectives. Neurophysiologie Clinique. doi:10.1016/j.neucli.2019.12.003
It doesn’t take much to affect the sensory input going to the brain. Scientists tried putting just 1mm of additional thickness under the big toes of female handball athletes. This infinitely small thickness changed the Centre of Pressure in the athletes. This study helps prove that there is so much potential in stimulating the bottom of the feet.
Viseux, F. (2019). Less than one millimeter under the great toe is enough to change balance ability in elite women handball players. Journal of Human Kinetics, 69, pp. 69-77.
Ankle sprains are one of the most common injuries, but they don’t just affect the one ankle.
Researches have found that the unaffected ankle is also affected. In one study, postural stability and neuromuscular control were significantly decreased in the unaffected ankles in those with recurrent ankle sprains.
As we know, when one joint or part of the body is compromised, the rest of the body compensates.
Lee, J.H., et al. (2008) Individuals with recurrent ankle sprain demonstrate postural instability and neuromuscular control deficits in unaffected side. Knee Surgery, Sports Traumatology, Arthroscopy. Doi: doi:10.1007/s00167-018-5190-1.
Collins, K.A. 2017. The immediate effects of plantar massage and textured insoles on gait in patients following ACL recontruction. Doctoral thesis, The University of North Carolina at Charlotte. https://search.proquest.com/openview/6d96b6ede4bfcceb3f1e7a9caa9e30a3/1?pq-origsite=gscholar&cbl=18750&diss=y
Steinberg, N. et al. 2015. Does wearing textured insoles during non-class time improve proprioception in professional dancers? International Journal of Sports Medicine, 36, pp. 1093-1099. http://dx.doi.org/ 10.1055/s-0035-1554633
Steinberg, N. et al. 2015. Use of a textured insole to improve the association between postural balance and ankle discrimination in young male and female dancers. Science & Medicine, www.sciandmed.com/mppa.
Steinberg, N. et al. 2016. Can textured insoles improve ankle proprioception and performance in dancers? Journal of Sports Sciences, 34:15, pp. 1430-1437. https://doi.org/10.1080/02640414.2015.1117120
Steinberg, N. et al 2016. The effect of textured ballet shoe insoles on ankle proprioception in dancers. Physical Therapy in Sport, 17, pp. 38-44. http://dx.doi.org/10.1016/j.ptsp.2015.04.001