U-TECH – the innovative technology
derived from biomechanical research, inspired by biological solutions
Biomechanical facts and truths
Studies conducted on more than 15.000 runners during prolonged running showed that the majority or more than 90 % of the observed runners hit the ground first with the heel or the rearfoot. Just 2 % of the runners under study were forefoot strikers, although 15 % were self-declared forefoot runners and 54 % self-declared midfoot runners. Therefore, the technology of the midsole and the outsole must meet the requirements of a rearfoot landing.
Most of the runners touch down with a slightly externally rotated foot. More than 90 % of the runners under study rotate the foot >8° outwards when landing. Thus, the construction of the posterior aspect of the sole must tolerate an outwardly rotated footstrike and the flex zones in the forefoot aspect of the sole has to meet the requirements of an outwardly rotated foot on the ground.
The activity of the dorsiflexor muscles of the ankle joint before landing affects a slightly supinated foot position at heel strike. Therefore, the foot lands first on the posterior lateral aspect of the shoe’s sole. The ground reaction forces during early landing act posterior outwards on the sole and on the rearfoot. Their line of action passes the ankle joint on the lateral side and – due to the laterally oriented tibia at first ground contact – the knee joint center on the medial side (see figure 1). Therefore, the acting forces, which have a lateral lever arm to the ankle joint, produce a torque to the ankle joint and cause the increasing pronation. The greater these frontal plane torques and the longer the duration of torque application are, the higher the pronation velocity and finally the maximum foot pronation will be.
On the knee, the ground reaction forces act medially from the joint center and produce an external adduction moment to the knee joint. This external adduction moment causes the adduction or the varus of the knee with increased loading on the medial compartment of the joint and an increased tensile stress on the lateral connective tissue and the lateral tendons and ligaments. The highest frontal plane moments and the highest compartment load occurs in mid-stance when the knee joint is maximally flexed.
With these dynamics at footstrike and during the initial stance, the rearfoot and the heel bone will be forced into an additional rotation around its vertical axis (rearfoot adduction). This rotation is immediately transferred to the talus, the bone between the calcaneus (heel bone) and the tibia. Finally the rotation is transmitted to the tibia and the shank. At the knee joint this movement initiated by the forces to the rearfoot occurs as the phenomena of internal knee rotation and internal torque.
Therefore, the cause of overpronation and increased knee adduction in running at footstrike and in early stance are the lateral torque and the rearfoot’s rotation around its vertical axis caused and forced by the dynamics during early stance.
The highest mechanical loading of the knee joint – especially while running –occurs in the middle of the stance phase when the knee has the maximum flexion of about 40 degrees. This is when the heel starts liftings from the ground and the entire load is transferred to the forefoot. In this phase of the stance the lateral external adduction moments at the knee reach their maximum and the internal knee rotation has its peak value (see figure 1, right).
Therefore, an innovative technology of the sole of a running shoe should not only consider the early stance with force application at the rearfoot but also the mid-stance, when the ground reaction force acts on the forefoot and the knee loading has maximum values.
Traditional and conventional sole constructions increase the lever arms of the acting ground forces to the ankle and knee joints through their wide-edged geometry and the everted rims, increase the external lateral torques to the ankle and knee joints and consequently enlarge knee adduction and internal rotation. It is to note that when running barefoot (which is not favorable at all for the majority of the population) the lateral lever arms of the forces acting from the ground to the leg are smaller at the ankle and the knee joints than when running in conventional running shoes. Hence pronation and knee adduction and internal rotation is smaller in running without shoe than in shod running. Conventional shoes causally increase the lateral instability and generally increase knee loading.
In barefoot running the force acting from the ground to the foot is centered under the hard and slim heel bone immediately after ground contact. The biomechanical solution comes from the fat pad around the heel bone which embeds the calcaneus in a ring-like or, more precisely, U-like manner. Figure 2 demonstrates MRI slices through the calcaneus and the surrounding fat tissue and gives an impressive picture of how the stiff and rigid bone is embedded into the soft and viscoelastic soft tissue.
The three-dimensional reconstruction (figure 3) of the fat pad of a healthy foot finds a ring-like organized structure with an ellipsoidal cross section and an anterior opening. With this structure the forces acting from the ground to the heel are centered in the center of the ring of the viscoelastic soft tissue around the heel and thus directly underneath the ankle joint. The anterior opening allows the controlled transfer of the point of force application to the forefoot in order to ensure the dynamic transition in walking and running. Therefore, the soft fat pad is not primarily a cushion element but acts, due to its deformability and its geometrical construction, ideally as a force centering system for forces acting from the ground when standing, walking and running. Like in a bowl or a spherical cap the acting force is forced to the center of the soft tissue ring, and the point of force application meets the calcaneus center and the vertical projection of the ankle joint.
A similar biological solution is shown in the knee joint. A flattened joint partner (the tibia plateau) meets a twofold convex joint partner (the femur condyles) and builds the knee joint. In order to stabilize and centralize this unstable construction, deformable and movable menisci surround the joint center and allow for a perfect centering of the joint force and the point of force application.
Inspired by these biological paradigms, the U-TECH technology was consequently derived and developed with the aim to center the forces acting from the ground to the foot and the leg in the center of the rearfoot and along the middle axis of the foot. With this technical solution lateral lever arms to ankle and knee joints are minimized and the cause of excessive pronation, knee adduction and internal rotation are counteracted sustainably.
U-TECH – the innovative technology
The U-shaped geometry of the circular and/or ellipsoidal TPU element in the posterior part of the sole (figure 4) ensures – like the fat pad under the bony heel bone – an immediate centering of the force acting from the ground to the foot at heel strike and during the early stance phase. Thus, the centered forces from the ground in the posterior part of the sole are underneath the centers of the ankle and knee joints. Frontal plane torques, which cause the rearfoot eversion, pronation, and adduction of the rearfoot and the adduction and internal rotation of the knee are reduced, minimized or even eliminated. Therefore, U-TECH acts on the cause of twisting and adducting the ankle and the knee joints and does not have to counteract the symptoms of foot pronation and knee adduction and internal rotation. Because the rearfoot sinks about 10 mm into the posterior U-TECH element within the first 50 ms, it is fully surrounded by the ring-like structure, movements of the rearfoot around the vertical axis are controlled and smoothly cushioned. With this technical solution rearfoot adduction and finally internal tibia rotation and twisting of the knee joint are limited or even eliminated.
Figure 4: U-TECH technology in the posterior (left in the picture) and anterior part of the sole (right in the picture).During the following phase of the stance, U-TECH centers the forces under the joint via guiding the point of force application through the anterior opening along the midline of the foot to the anterior U-TECH element of the front part of the sole. U-TECH has the potential to minimize the cause of detrimental and performance-decreasing adduction, rotation, and twisting of the joints throughout the entire transition from heel to toes, and especially during the highest loading phase at maximum knee joint flexion, in every step and during the entire run.
The consequence is a reduction of lateral torques at the ankle and knee joints during the entire stance. Figure 5 demonstrates the – in comparison to figure 1 – changed dynamics at ankle and knee joints with U-TECH technology. The decreased lateral lever arms of the forces acting from the ground on the runner reduce the lateral torques and in consequence the detrimental lateral tilting and twisting of the ankle and especial the knee.
Complementary the technical solution reduces the muscle forces inefficient for the locomotion and finally the entire muscle work through the decreased lateral torques. Running at the same speed should requires less muscle work and locomotion should be more efficient. U-TECH offers the runner an unusually light transition from heel to toes and a unique experience of a dynamic ride.
Figure 5. U-TECH: Acting forces at heel strike (left), at load acceptance (middle) and at maximum knee joint loading at mid-stance (right) when running in Nevos with U-TECH technology. Left: The ground reaction force (force acting from the ground on the runner) (red arrow) is located on the backend of the sole and shows a smaller lateral lever arm to the ankle joint through the ring-like circular U-TECH element (red circle). Center: The result of this force application is a clearly reduced counter-clockwisely acting lateral torque (black arrow), which causes significantly less pronation and pronation velocity. Right: During mid-stance the ground reaction force (red arrow), which passes the knee less medially than in conventional shoes, causes a clearly decreased external adduction moment (lateral torque) to the knee joint followed by less adduction or varus of the joint with minor medial compartment compression load and decreased tension on the lateral side.
- U-TECH is strictly derived from scientific research and biomechanical knowledge and uses biological solutions as technical paradigms.
- U-TECH therefore has the potential to reduce and even to avoid unneeded and harmful loading and unnecessary joint motion in secondary planes of motion.
- U-TECH combines as the first functional midsole technology the biomechanical paradigms of injury prevention, performance enhancement and improvement of comfort.
- U-TECH offers the prerequisites for low-risk, enjoyable runs and generally a unique lightness of locomotion.