It has been demonstrated that, by varying the mechanical properties of footwear, the sprinting performance can be improved. It has been hypothesized that, for maximal performance, tuning the shoe stiffness to the requirements of the athlete is necessary. The aim of this study was to investigate the feasibility of using sprint shoes constructed with selective-laser-sintered Nylon 12 sole units for sprint-related jump tasks and to examine whether adaptations to the mechanical properties of the footwear were sufficient to elicit changes to lower-limb dynamics during athletic performance. An internationally competitive sprinter completed sprint-related jump metrics in various selective-laser-sintered shoes with bending stiffnesses of 9 N, 24.5 N, and 38 N in flexion and 7.4 N, 14.7 N, and 26.1 N in extension. The participant performed best in the medium-stiffness shoe for squat jumps and the maximum-stiffness shoe for bounce drop jumps. This investigation has demonstrated that selective laser sintering can produce high-integrity footwear with markedly different mechanical properties. Such footwear, coupled with an appropriate test method, has been shown to be suitable for investigating the relationship between lower-limb dynamics and shoe stiffness.

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A novel method for incorporating traction features within sprint shoe sole units using laser sintered nylon-12 was investigated. The design, manufacture, and mechanical testing of the sprint shoe sole units are detailed. Three proof-of-principle concept sole units, incorporating traction features typically embodied in commercially available sprint shoes, were developed and manufactured using laser sintered nylon-12 and assembled with standard sprint shoe uppers. The traction properties of both commercially available and laser sintered outsoled sprint shoes were tested on a bespoke rig. Under the prescribed testing conditions, the laser sintered outsoled sprint shoes compared favourably with the commercially available sprint shoes, with the laser sintered concept shoes generating mean peak traction forces to within 15 per cent of those exhibited by an individual commercially available sprint shoe. The results indicate the potential to create a fully functional sprint shoe sole unit using laser sintering technologies, and thereby to create one-off sprint shoes for athletes, is viable in terms of the shoe being able to provide traction levels close to conventional sprint shoes. However, as the strain rates encountered during sprinting are considerably higher than in the test methods implemented, further human performance testing is recommended.

This study could not detect any pronounced differences between the two accelerometer measurements during walking or running. There were, however, small differences in amplitude and phase which need to be quantitatively investigated as they may point at subtle differences between in-shoe and outshoe movement characteristics (Figures 1 and 2). This would be in line with Reinschmidt et al.'s study, which showed notable differences between measurements from inside and outside the shoe using markerbased measurements. However, these differences were found in inversion during side-cutting movements, measured with MoCap (Reinschmidt et al. 1992). In the present study only straight forward treadmill running was used.Further studies that include side-cutting and unrestrained movements are needed in order to determine whether there are differences between in-shoe and out-shoe accelerometry measurements of the rearfoot.