What is balance in skiing?
It depends on who you ask. The only limitations seem to be the imagination of the various authorities in skiing.
Typical explanations of balance don’t differentiate between balance associated with staying upright by any and every means and the sophisticated, subconsciously mediated, processes of balance responsible for the maintenance of upright postures and locomotion. The latter involves the management of forces in the feet or foot between the soles of the feet or foot and ground. The coordination and orchestration of these forces by the CNS, maintains the position of center of mass (COM) within the physiological limits of the base of the support in a state of dynamic equilibrium. In laboratory environments, where balance has been studied so throughly it can be analyzed and quantified, balance is expressed by the relationship of the center of pressure or COP (the point center of ground reaction force) with COM. The location and excursion of COP is indicative of the position of COM as expressed by the gravity line, G, or resultant force, R. No physical forces associated with balance activity are present in the sagittal (side-to-side) or coronal (front-to-back) planes. The balance process is mediated entirely by the central nervous system (CNS) at a subconscious level. Given the extreme sophistication of the hard-wired mechanisms of balance we were born with, there is no valid reason why balance in skiing should be any different.
Without knowing where the forces in the feet should be and how and where they should move, we have no idea how to balance perfectly on our outside ski as those such as Marc Giardelli and other world class racers and elite skiers have alluded to for decades; let alone have any idea of what balancing on the outside ski should feel like.
Two studies done in 1998 by a team from the University of Ottawa provide some insights.
ANALYSIS OF THE DISTRIBUTION OF PRESSURES UNDER THE FEET OF ELITE ALPINE SKI INSTRUCTORS: Dany Lafontaine, M.Sc.1,2,3, Mario Lamontagne, Ph.D.1,2,3, Daniel Dupuis, M.Sc.1,2, Binta Diallo, B.Sc.1,2,3. Faculty of Health Sciences1, School of Human Kinetics2, Department of Cellular and Molecular Medicine, Anatomy program3, University of Ottawa, Ottawa, Ontario, Canada.
“Thanks to recent developments in biomechanical instrumentation, research on alpine skiing can now be performed in on-piste situations. Therefore it would be of interest to determine what is happening under the feet of high level non-racers, such as ski instructors (my emphasis added).
“Three highly skilled ski instructors (CSIA level IV) consented to serve as subjects for this study. Their usual ski boots were fitted with pressure sensitive insoles linked to the PEDAR mobile system which they wore on their backs (Novel corporation, Munich). With their boots so equipped, the subjects performed a variety of turns of controlled radii on a groomed piste. The turn radii were controlled by markers on the snow surface, and were consistent with the guidelines of the Fédération Internationale de Ski, for turn size. Subjects skied on a groomed piste, while the PEDAR system recorded pressure data (sampling rate 50 Hz) onto a memory card. A video (60 Hz) recording of their ski runs was also made to facilitate analysis.
“What has come out of the results at this point of the study, is that the pressure recorded under the feet can be quite high. The highest pressures are measured on the medial parts of the heel, as well as the medial parts of the forefoot (under first metatarsal). The centre of pressure travels from under the first metatarsal joint down to under the medial part of the heel of the skiers, as they make their way through the turn (my emphasis added), These highest pressures reach up to 30 newtons per square centimetre. Force-time histories reveal that forces of up to 3 times body weight can be attained during high performance recreational skiing (my emphasis added).
“It is quite likely that the type of equipment (skis and boots) worn by the subjects had an effect on the values obtained (my emphasis added). The individual technical adjustments of the skiers may have also had an effect on the measurements. One thing is certain, the centre of pressure moves from the front medial part of the foot, back towards the medial side of the heel as the skiers progress through the turns.”
ANALYSIS OF THE DISTRIBUTION OF PRESSURE UNDER THE FEET OF ELITE ALPINE SKI INSTRUCTORS: Dany Lafontaine, Mario Lamontagne, Daniel Dupuis & Binta Diallo, Laboratory for Research on the Biomechanics of Hockey, University of Ottawa, Canada – Proceedings of the XVI International Symposium on Biomechanics in Sports (1998), Konstanz, Germany, p.485.
“In alpine skiing, the feet are used as both a steering device and an important source of sensory input (my emphasis added). It has become quite common for instructors and coaches to ask their pupils to feel pressure under certain parts of their feet in order to ski better. It has also been a trend in skiing to inform students to initiate turns through the application of pressure in the forefoot area and to progressively “roll” from the front to the back of their feet. All of these instructions rely on master instructors’ perceptions of what they feel while executing a ski turn. Historically, it has been quite complicated to perform biomechanics research on alpine skiing on-site. This fact is so because of the environment where the sport is practised which does not lend itself well to biomechanical measures using traditional equipment.
“The trajectory of COP was consistent between both feet for all turn types (my emphasis added). Results showed the COP following a near linear trajectory for the Dynamic Parallel, Short Radius and Basic Parallel turns. This trajectory had the COP move from the head of the first metatarsal at the beginning of the turns, and progressively migrate towards the medial aspect of the longitudinal arch near the end of the turns (my emphasis added). However, the COP travelled from the head of the first metatarsal to the medial aspect of the heel during Giant Slalom turns
“A factor that was not controlled during data collection was the equipment worn by the subjects. The skiers wore different boots, and used different skis, although two of them had the same brand and model of skis and boots. It still has yet to be determined if that factor had any effect on the results. A point that all the skis that the subjects used had in common is that the skis were all sharp side-cut skis (also called shaped skis). Another equipment variation which may have affected in-boot measurements, is that some subjects (n=5) wore custom designed footbeds, while the other did not (my emphasis added). As was stated for the skis and boots, it has yet to be determined if this piece of equipment affected results or not.”
- Every instructor in both studies, without exception, initiated their turns with high pressure under the head of the first metatarsal of their outside foot in the turn. This is a clear indication that not just pressure, but high pressure under the first metatarsal, is fundamental to the technique of elite skiers.
- These studies were published 17 years ago. Yet even though Shiffrin stresses the importance of ‘getting over it’ (the head of the first metatarsal) and Ligety talks about ‘creating pressure’, there is little or no mention in the technical narrative of skiing of the need to establish pressure under the head of the first metatarsal at the initiation of a turn.
- All the instructors in the two studies were elite skiers. Yet there were significant differences between the two groups of instructors in each study. In the first study, the data showed that COP at the beginning of a turn was under the head of the first metatarsal and moved to the medial (inner) aspect of the heel near the end of a turn whereas in the second study COP at the beginning of a turn was under the head of the first metatarsal and moved only slightly rearward to the medial aspect of the longitudinal arch near the end of the turn.
- The studies did not look for forces in other planes so did not confirm that the instructors were in ‘balance’.
- It was only in the GS turns that COP moved to the medial aspect of the heel. The question is why did COP move rearward at all towards the end of any turn types?
- The only way COP can act under the head of the first metatarsal is through pronation. This requires that the foot be flat on snow either between edge change at the end of the transition or from a flat landing on the outside foot/ski in the fall line. Even then, the boot must not interfere with the ability of the the foot to pronate.
In my next post, I will discuss the implications of the University of Ottawa studies.