BackgroundAchilles tendon injuries are known to commonly occur in runners. During running repeated impacts are transferred in axial direction along the lower leg, therefore possibly affecting the oscillation behavior of the Achilles tendon. The purpose of the present study was to explore the effects of different footwear modifications and different ground conditions (over ground versus treadmill) on oscillations at the Achilles tendon.MethodsOscillations were measured in 20 male runners using two tri-axial accelerometers. Participants ran in three different shoe types on a treadmill and over ground. Data analysis was limited to stance phase and performed in time and frequency space. Statistical comparison was conducted between oscillations in vertical and horizontal direction, between running shoes and between ground conditions (treadmill versus over ground running).ResultsDifferences in the oscillation behavior could be detected between measurement directions with peak accelerations in the vertical being lower than those in the horizontal direction, p < 0.01. Peak accelerations occurred earlier at the distal accelerometer than at the proximal one, p < 0.01. Average normalized power differed between running shoes (p < 0.01) with harder damping material resulting in higher power values. Little to no power attenuation was found between the two accelerometers. Oscillation behavior of the Achilles tendon is not influenced by ground condition.ConclusionDifferences in shoe configurations may lead to variations in running technique and impact forces and therefore result in alterations of the vibration behavior at the Achilles tendon. The absence of power attenuation may have been caused by either a short distance between the two accelerometers or high stiffness of the tendon. High stiffness of the tendon will lead to complete transmission of the signal along the Achilles tendon and therefore no attenuation occurs.

may be different for female players. Research should investigate, whether these differences in foot placement have performance or injury-prevention related consequences, which could be influenced by footwear design. Playing behaviourThe playing behaviour of men and women during a soccer game differs. For instance: men perform more high intensity runs (2.43 km) compared to women (1.32 km). However, total distance, covered during a game, varies only little (men 10-14 km; women 10.3-10.4 km) (Mohr et al. 2003, Krustrup et al. 2005.Due to the lower muscle mass and strength women use more frequently the full instep and instep kick for distances where men can still use more accurate inside kicks . For soccer shoe design the different frequency of used kicking techniques between women and men are of special interest. Player preferencesA questionnaire was distributed to 105 male and 200 female soccer players to find out which characteristics of soccer shoes are most important for them and to identify which parts of their shoes should be modified. Both sexes ranked injury protection very low with even less importance for the men. For both genders comfort, ball sensing, traction and stability are the most desirable shoe features. Thirty-five per cent of the female and 18% of the male players want a narrower midfoot region. Nearly 40% of the women against 25% of the men prefer a more flexible outsole and 37% against 26% want a softer upper material (Althoff and Hennig 2012). ConclusionLower muscle strength of women, different movement patterns, and a higher injury risk should influence stud configuration and design of female soccer shoes.Questionnaires showed that many female soccer players are not satisfied with their shoes. They want a better fit, a more flexible outsole, and a softer upper material.

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