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EpicSki › Gear Articles › The Birdcage Boot Experiment By David Macphail

The Birdcage Boot Experiment By David Macphail

The Birdcage Experiments

by David MacPhail

In the summer of 1991 a science team that Steve Podborski and I had assembled to develop a new ski boot conducted pioneering experiments on the Blackcomb Glacier with a device we affectionately named the “Birdcage.” The Birdcage connected a rigid structure to the foot at very specific points while leaving the remaining areas of the foot free of any constraint. The object of the experiments was to study the effects on balance of specific forms of constraint applied to the mechanical points of the foot we had previously identified. The experiments were designed according to a scientific protocol that standardised conditions from test to test while varying one component at a time.

For example, to study the effects of cuff forward lean angle on specific muscles, the range of rotation of the cuff was kept the same from test to test while the initial angle at which the cuff was set was varied from test to test. The cuff was fit tightly about the leg so as to reduce to a minimum any effects of movement of the leg within the cuff. Other aspects of the test such as position of the heel and ball of the foot in relation to the centreline and inside edge of the ski were kept the same.

By using such test protocols we could study the firing order and pattern of specific muscles. This data could then be used to determine the order of events such as balancing, steering and edging. It was discovered that by varying the conditions that affected the firing and effectiveness of the soleus muscle, it could be played like a musical instrument. For example, if the cuff angle were set so it was too erect the soleus would make multiple attempts at the start of each turn to try and get CM over top of and in front of the ankle.

Our primary tester for the experiments was Olympic bronze medallist and World Cup downhill champion Steve Podborski. Steve is shown to the left trying on the Birdcage. The cable coming out of the rear of the device is connected to a Toshiba optical drive computer (remember, this is 1991) that Toshiba loaned us in support of our program. Since telemetry was too costly and less positive we used a 1200 ft cable that linked the Birdcage to a computer that was set up in a tent. Although the technician could not see the skier, he could easily assess their technical competence within a short period of time by assessing the data generated. This was even more remarkable considering that the technician had no background in skiing or ski teaching.

The testers wore a harness to keep the cable from interfering with their movements. A chase skier ensured that the cable remained behind the testers and did not pull on them.

Of interest is the fact that this work was universally regarded within the ski industry as completely irrelevant to skiing.


Comments (4)

This is fantastic..... what were the findings??
Real Science! More, More, More.......
Was this published?
Don't tease us with the experiment without reporting the findings!
Those interested in more information on the Birdcage Experiments and the mechanics, biomechanics and physics of World Cup Ski Technique please check out my blog - skimoves.me
EpicSki › Gear Articles › The Birdcage Boot Experiment By David Macphail