According to Benno Nigg, no one knows for sure. From 1981 until he retired recently, Nigg founded and was the Director of the Human Performance Laboratory (HPL) at the University of Calgary in Calgary, Alberta, Canada. The Human Performance Laboratory is a multi-disciplinary research centre concentrating on the study of the human body and its locomotion. From 1971 until 1981, Nigg was the Director of the Biomechanics Laboratory at ETH Zurich (Swiss Federal Institute of Technology).
For more than 30 years, Nigg studied the effects of insoles and orthotics on the lower limbs. What he found was that most of the time they didn’t do what was claimed. Often, the effect of the same insole or orthotic varied greatly from one subject to another even though they had the same condition. In some cases, Nigg found that orthotics had a large effect on muscles and joints, increasing muscle activity by as much as 50% for the same movement while increasing stress on joints by the same amount as the body fought to overcome the effect of the orthotic. Nigg also found that “corrective” orthotics do not correct so much as lead to a reduction in muscle strength. He details his findings in his book, Biomechanics of Sports Shoes. The book can be ordered from NiggShoeBook@kin.ucalgary.ca
If no one knows what insoles and orthotics in footwear affect the user, how is it possible for anyone to know insoles and orthotics in ski boots affect skiers? I am not taking about claims made for insoles and orthotics made for ski boots. I am talking about how they affect the skier during ski maneuvers as confirmed by on-snow studies. The pivotal issue is how the CNS manages, or isn’t able to manage, the forces across the inside edge of the outside ski in a turn. This is what any claims should focus on. But I have yet to find evidence that any studies to this effect have been done.
You’ve been to a ski boot-fitting shop or perhaps a foot professional and had custom insoles or orthotics made for your ski boots. You may have been told that these interventions will create a specific alignment of your knees with some aspect of your feet. You may have also been told that your feet pronate or over-pronate and that insoles or orthotics will correct these issues. In addition, you may have been told that you will ski better with the insoles or orthotics or an expectation was created that you would. This expectation may have been reinforced by the fact that you probably felt very different standing in your boots with the insoles or orthotics fit to them than you did without them.
Out on the ski hill with your boots and skis on you probably also felt different than you did without your new insoles or orthotics. But are you skiing better? You might think you are, especially after paying several hundred dollars or more. But how do you know for sure? You don’t. Unless the person who made your custom insoles or orthotics instrumented your ski boots and captured data during actual skiing both before and after the insoles or orthotics were installed and then compared the data sets to peer reviewed, independent studies that provided compelling evidence that the data captured during skiing conclusively demonstrated a positive effect of the insoles or orthotics on your skiing, any claims made were speculative and any conclusions, subjective. More important, claims tend to be biased because a product is associated with them.
You are probably thinking that none of this matters because there is an abundance of science in support of custom insoles and orthotics. But in a New York Times article, Close Look at Orthotics Raises a Welter of Doubts – January 17, 2011 (http://www.nytimes.com/2011/01/18/health/nutrition/18best.html?pagewanted=all), Benno Nigg looked critically at insoles and orthotics. His overall conclusion? Shoe inserts or orthotics may be helpful as a short-term solution, preventing injuries in some athletes. But it is not clear how to make inserts that work. The idea that they are supposed to correct mechanical-alignment problems does not hold up.”
In the same NY Times article, Scott D. Cummings, president of the American Academy of Orthotists and Prosthetists, acknowledged that the trade is only now moving toward becoming a science and that when it comes to science and rigorous studies, “comparatively, there isn’t a whole lot of evidence out there.” Dr. Nigg would agree. The proof that orthotics provide benefit? Some people feel better using them than not using them. So any evidence is in the form of highly individualized, subjective feel. What about skiing? Is claiming that the foot needs to be supported and/or especially that the foot functions best in skiing when its joints are immobilized in neutral, sufficient to claim a benefit or implied need for insoles or orthotics in skiing? Hardly.
The first thing to consider is that unless the load W from the central load-bearing axis is transferred to the inside turn aspect of the inside edge of the outside ski it is impossible for the foot to pronate. In addition, in this configuration, the outside foot cannot be ‘supported’ because there is no support in the form of a contiguous source of snow reaction force under the base of the outside ski.
When Lange introduced the world’s first all plastic ski boot in in 1962, biomechanical research on human locomotion was in its infancy. Biomechanical studies of sports shoes, including ski boots, were nonexistent. The first edition of Inman’s seminal work, The Joints of the Ankle, wasn’t published until 1976. What did it take for the new rigid plastic ski boot to be universally accepted? A few trips to the podium.
When running and jogging took off in the early 1970s, insoles and orthotics and were widely promoted in response to injuries that were erroneously assumed to be caused by excessive (over) pronation. Were there any studies to support this conclusion? No. Nor, was there any evidence that I am aware to support the position of the proponents of insoles and orthotics that the foot needed or would benefit from support in ski boots. As far as I have been able to determine, the need to support the foot in a ski boot was and still is based on a widely accepted assumption. If pronation was a problem in running, then it had to be a problem in skiing. That made sense. Except that it didn’t. In the late 1980s and early 1990s, studies were showing that there was only minimal correlation between high pronation and high impact loading and typical running injuries. Nigg and other researchers suggested that no evidence was found because there was no evidence. Researcher had been trying to prove pronation was the cause of running injuries instead of trying to find the cause.
Two recent studies question the validity of the premise of supporting the longitudinal arch of the foot, especially in ski boots.
Dynamic loading of the plantar aponeurosis in walking http://www.ncbi.nlm.nih.gov/pubmed/14996881
BACKGROUND: The plantar aponeurosis is known to be a major contributor to arch support, but its role in transferring Achilles tendon loads to the forefoot remains poorly understood. The goal of this study was to increase our understanding of the function of the plantar aponeurosis during gait. We specifically examined the plantar aponeurosis force pattern and its relationship to Achilles tendon forces during simulations of the stance phase of gait in a cadaver model.
RESULTS: Plantar aponeurosis forces gradually increased during stance and peaked in late stance. Maximum tension averaged 96% +/- 36% of body weight. There was a good correlation between plantar aponeurosis tension and Achilles tendon force (r = 0.76).
CONCLUSIONS: The plantar aponeurosis transmits large forces between the hindfoot and forefoot during the stance phase of gait. The varying pattern of plantar aponeurosis force and its relationship to Achilles tendon force demonstrates the importance of analyzing the function of the plantar aponeurosis throughout the stance phase of the gait cycle rather than in a static standing position.
For years, experts have claimed that skiing is done in the mid phase of stance in what is called the gait cycle. What the preceding study clearly shows is that the strongest stance in skiing in terms of the ability to transfer force to the head of the first metatarsal and functional stability of the structures of the foot occurs in the late phase of stance, not the mid phase. The graphic below provides a simulated representation of the sequence by which Achilles tendon force tensions the plantar aponeurosis and transfers large forces to the forefoot, especially to the head of the first metatarsal.
New studies are questioning the premise of supporting the arch of the foot with anything because neural activity in the arch of the foot appears to be potentiated by tension in the plantar aponeurosis and surrounding soft tissue. Rather than being a passive static entity in its role as a support structure for the superincumbent body, the arch is a dynamic, neurally charged system whose height changes in response to changes in perturbations in GRF that challenge the balance system.
Foot anatomy specialization for postural sensation and control http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3311689/
These findings show that rather than serving as a rigid base of support, the foot is compliant, in an active state, and sensitive to minute deformations. In conclusion, the architecture and physiology of the foot appear to contribute to the task of bipedal postural control with great sensitivity. Here, we show that the foot, rather than serving as rigid base of support, is in an active, flexible state and is sensitive to minute perturbations even if the entire hind and midfoot is stably supported and the ankle joint is unperturbed.
However, support of the body weight in the erect posture involves not only the counterbalancing of the gravitational load, but also equilibrium maintenance, which is dynamic in nature. Accordingly, somatosensory information on local foot deformations can be provided from numerous receptors in the foot arch ligaments, joint capsules, intrinsic foot muscles, and cutaneous mechanoreceptors on the plantar soles (Fallon et al. 2005; Gimmon et al. 2011; Kavounoudias et al. 1998; Magnusson et al. 1990; Meyer et al. 2004; Schieppati et al. 1995).
During standing, the foot arch probe and shin sway revealed a significant correlation, which shows that as the tibia tilts forward, the foot arch flattens and vice versa.
It is worth stressing that the foot represents an important receptive field, formed by numerous skin, joint, tendon, and muscular receptors (including intrinsic foot muscles), and it has long been recognized that damage to the foot, be it either by sensorineural loss or physical damage to the muscles, bones, or supporting tissues, changes posture and gait stability.
A number of cutaneous and load-related reflexes may participate in the fine control of posture or foot positioning during walking.
Almost any structure that provides even minimal support for the arches of the foot will prevent the arch from lowering and transferring force to the MTs and will interfere with the function of the arch as an active, dynamic neuro-sensory mechanism.
Claims made for insoles and orthotics create a reasonable expectation in the consumer that what is experienced in an off hill controlled environment will also happen on the ski slopes. Terms of disclosure require that any claims be qualified with statements like, “These claims have not been confirmed during actual ski maneuvers”.