To investigate the influence of the 'kyBoot' and 'Joya' shoes designed by Karl Müller Sr and Jr on gait when walking and running, and on the forces affecting the feet, the Biomechanics Institute at ETH Zurich (the Swiss Federal Institute of Technology) carried out a study including gait analysis. The study involved 12 test subjects (barefoot, kyBoot, Joya, MBT and 3 test subjects with Joyssy), high-speed videos of the heel strike, kinetic measurements of the ground reaction force and kinematic measurements of the body position and movement.
Summary of conclusions:
1. kyBoot/Joya trigger greater movement. This is a predictable result, as the soft, supple design of the sole makes it extremely yielding. When we walk barefoot on an uneven, natural surface (in sand, uphill, downhill, etc.) the angles of movement are naturally greater, of course. With the soft, supple design it can be assumed that more effort is required, more energy is used and the muscles get more exercise.
2. With Karl Müller (kyBoot) shoes the movement curves are generally smoother (less jerky).
3. In the initial heel-strike phase the force acting on the body is considerably lower (by a factor of 2–5) than during barefoot walking/running due to the shock-absorbing properties of the Karl Müller shoe soles.
4. No differences were established between the Karl Müller shoes and those with rounded soles regarding upper body posture.