Walking, Running, and Gliding: The Biomechanics and Energetics of Diagonal Stride Skiing

Diagonal stride is the classic style of cross-­‐country skiing involving alternating arm and leg movements that appear similar to both walking and running, but is it truly biomechanically and energetically similar to walking and running? To better understand the fundamental biomechanics of diagonal stride skiing, we compared its ground reaction forces, mechanical energy fluctuations of the center of mass and metabolic energy consumption to walking and running. We hypothesized that diagonal stride skiing would be biomechanically more similar to running, but with a lesser energetic cost. I recorded ground reaction forces of nine subjects roller skiing on a force-­‐measuring treadmill, a method that catalyzed the study of walking and running but had never been utilized in cross-­‐country skiing studies. I analyzed the changes in the perpendicular and parallel forces with increasing speed (1.25 and 3 m/s) and incline (Level, 3°, and 6°). Force recordings were similar to those previously recorded with other devices, thus validating our method. From the forces, we calculated the mechanical energy fluctuations of the center of mass of level walking, running, and diagonal stride skiing (with and without poles). Diagonal stride skiing had almost in-­‐phase fluctuations of kinetic and gravitational potential energies, similar to running. In-­‐phase fluctuations of the center of mass allow runners to store and recover elastic energy, so that less mechanical energy input is required with each step. However, in diagonal stride skiing, almost all of the kinetic energy losses were due to the rolling resistance of the skis and could not be stored elastically. I also compared the energy expenditure of each locomotion form using open-­‐circuit expired gas analysis. Diagonal skiing had a metabolic rate greater than walking and lower than running at the same speeds. Also, I found no significant metabolic advantage of using poles during level roller skiing. Overall, by successfully using a force-­‐measuring treadmill, I found that diagonal skiing is a unique form of locomotion that does not utilize elastic energy storage like running, but has a lower energeti