Standardized procedure to measure ankle range of motion of ski mountaineering boots

The interest in ski mountaineering is growing a lot in recent years both as a hiking activity and as a sports activity. Skiers moving uphill require equipment that is ever lighter and that does not impede the stride while walking. Manufacturers do not use the same procedure to measure the flex-extension angle of the ankle allowed by the boot, hindering the comparison between different boots with respect to this parameter. The present study seeks to define a procedure that can be adopted by all manufacturers and that is based on data that are plausible as they are derived from tests performed under real conditions. To identify the trends of the angles between the leg and the boot the tests were carried out in the laboratory. Boot leg angle ranges between 29.97±1.71° and 21.06±0.79° respectively for wider boot and lower boot in flat conditions, and between 26.6S±0.54° and 19.73±0.64° in steep conditions. To have more realistic data the subsequent tests were therefore conducted on snow. Seven male athletes performed on three different slopes wearing seven different ski boots. Different from the treadmill, on flat, the leg is more upright and strains more on the rear part of the boot, while, more similar to the lab, at the maximum slope, the leg remains more inclined, loading the front part of the boot. Cycle time and minimal leg inclination increase with the slope while maximal leg inclination is reduced. The angular range of the ankle and the maximum forward effort depend on the slope and the boot model, while no effect of the boot was found on the effort on the rear of the boot. The data of the flexion-extension torque during walking, calculated starting from pressure data, allowed to define a standardized limit torque for the displacement of a leg section with defined geometry based on 3D scans of the limbs of the participants. The value of the angle of flexion and extension of the leg with respect to the shell is acquired by an accelerometer placed on the center of rotation of the ankle joint. A tool has been developed to implement the procedure and obtain the forward and backward inclination of the leg allowed by the boot, at the standardized torques, to warranty skiers to have an extra element of comparison to consciously choose the boot that best suits their needs.