LEFT-RIGHT PRESSURE DIFFERENCES: THE BIG PICTURE


The University of Ottawa foot pressure studies, that used elite ski instructors, noted that the averaged maximal pressures were relatively similar for all types of turns ranging from 28 to 38 N/cm 2 (Table 2). The maximum pressures obtained during all types of turns reached up to 45 N/cm2 for one of the subjects while performing Short Radius turns. Of interest to the researchers was the apparent trend for peak forces to be higher under the left foot in three out of the four types of turns. While the researchers offered no explanation for this variance they noted:

“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.”

I was involved with foot pressure studies in 2001 using the same Novel Pedar system as the University of Ottawa researchers. In looking at their data, it appears as if the Novel Pedar system my team used had more sophisticated software.

The image below shows a screen image of Pedar data file from the skier in the right hand frame.

L-R Pressure Differences

(click on the image to enlarge)

As with the University of Ottawa studies, the Pedar pressure data was synced to video of the skier.

The lines radiating from the heel to the ball of the foot are what are called ‘excursions’ of center of pressure or COP. The red lines are the excursions from the heel to the head of the first metatarsal. The blue lines are excursions from the forefoot to the hindfoot. The red dot is the COP under the head of the first metatarsal. The blue dot is COP under the heel.

Note the dramatic differences in the pressure patterns between the left and right feet; the same pattern seen by University of Ottawa researchers. The pressure pattern, especially the excursions, is much tighter under the left foot than the right foot while the pressures on the right foot are literally ‘all over the pressure map’.

  • Note the position of the red dot representing COP in the left foot. COP is over the inside edge whereas it is more towards the outboard side of the turn in the right foot and less localized.
  • The pressures under the heel of the right foot are much higher than the pressures under the heel of the left foot; 6 N/cm2 vs 10 N/cm2, not good.
  • Note also that the excursions of COP radiate to the 1st, 2nd and 4th toes in the right foot whereas COP never exceeds the limits of the head of the first metatarsal in the left foot.

It should be obvious on which side the turns are better. The preceding data is an example of some of the best data captured from an elite skier. The skier is a former World Cup champion. The pressure pattern of the right foot indicates significant functional issues.

A starting point would be a comprehensive functional assessment of the skier.

 

10 comments

  1. I find all of these studies interesting, however, if we really want to help skiers be more efficient and effective, wouldn’t it make sense to share personal experiences on what problem/problems we were having, what we tried and what was the effect??? I’ve skied for over 60 years, since leather boots have had a “balance” problem. Tried many different boots. Some were better than others. Can’t tell you why. Have four pair of boots, Head B 3s, Lange sx 120 and K2 Spyne yeah, touring boots La Sportiv. On soft snow/powder I’ll take the La Sportiv really great feel and balance. Langes just dont’ feel right (I think it’s either lack of forward lean or flex point or ???) Heads allow no ankle articulation. Love the fit and flex of the K2’s but can’t figure out how to cant them ?? I’m naturally over canted 2.5 degrees on the left leg (speed wobble lower third of turn on harder snow) and 2 degrees under canted on the right side. I’ve also been told that my left foot is “locked”. My tech is a “master boot fitter”. Have foot beds in all but the sportiv boots. I’m not sure that the foot beds are a plus or maybe even a minus ???? I’m going to try my K2’s without the foot beds and see what happens. Any ideas are greatly appreciated

    1. I agree. I am about to start posting on my work with local Whistler-Blackcomb Ski Pro, Matt Williams. I decided to work with a few local skiers last fall because it would give me an opportunity to document changes made to their equipment and how it affected their technique. In many ways, this is far more useful to those such as yourself because the Shiffrins, Vonns and Ligetys of the ski world would not be where they are if they had the kind of boot problems you are having.

      I have very structured system for making changes to ski boots that makes it easy for the skier to determine whether a change is positive or negative. After my next post, I will be posting on Matt’s boot modifications.

    1. Assuming an actual limb length discrepancy, I concur that 1.2 cm will not cause a problem. External rotation of one or both legs of more than 10 degrees will cause problems.

  2. Among many of the PTs I know, asymmetry is considered normal not abnormal. This study is of a very small sample. Do you know if they were all R foot dominant? I’m also assuming that the slope the study was done on did not have a double fall line.

    1. Actually, this sort of garbage data was typical of what we got under ALL conditions. At least some of the problems were caused by the boots. But without putting the subjects through a comprehensive functional assessment and proceeding in a structured analytical manner, it is not possible to arrive at any meaningful conclusions as to what caused what. As far as I know, the Birdcage studies were the only studies I am aware of that were ever done that got reasonably clean data. So here’s a question for you Ellen. Why isn’t the ski industry spending hundreds of thousands of dollars or even a few hundred dollars, studying the effect of ski equipment on the user or looking for ways to make skiing easier and especially SAFER? Over to you Ellen.

  3. Not surprised there were right-left differences. Most people are right handed, and would choose to kick a ball with their right foot. Also, very few people are structurally symmetric, and about 25% of the male population have a 1.2cm or greater leg length discrepancy. I do, and I know that I turn more easily on skates when going around a corner to the left, so my longer leg is on the inside of the turn…when turning in the opposite direction I look like I have cerebral palsy. Same with skiing…when turning, and stopping, I know my two legs and feet behave differently.

    1. This is a good example of where a picture really is worth a thousand words. Raw pressure numbers reveal very little of the underlying dysfunction. It seems as if humans are naturally neurally asymmetric even when they are within reasonable functional tolerances (not many are). Perhaps someone will invent a technology that reformats the CNS or at least makes it more symmetrical.

Comments are closed.