Abstract
BackgroundIndividual compliances of the foot-shoe interface have been suggested to store and release elastic strain energy via ligamentous and tendinous structures or by increased midsole bending stiffness (MBS), compression stiffness, and resilience of running shoes. It is unknown, however, how these compliances interact with each other when the MBS of a running shoe is increased. The purpose of this study was to investigate how structures of the foot-shoe interface are influenced during running by changes to the MBS of sport shoes.MethodsA randomised crossover trial was performed, where 13 male, recreational runners ran on an instrumented treadmill at 3.5 m·s−1 while motion capture was used to estimate foot arch, plantar muscle-tendon unit (pMTU), and shank muscle-tendon unit (sMTU) behaviour in two conditions: (1) control shoe and (2) the same shoe with carbon fibre plates inserted to increase the MBS.ResultsRunning in a shoe with increased MBS resulted in less deformation of the arch (mean ± SD; stiff, 7.26 ± 1.78°; control, 8.84 ± 2.87°; p ≤ 0.05), reduced pMTU shortening (stiff, 4.39 ± 1.59 mm; control, 6.46 ± 1.42 mm; p ≤ 0.01), and lower shortening velocities of the pMTU (stiff, − 0.21 ± 0.03 m·s−1; control, − 0.30 ± 0.05 m·s−1; p ≤ 0.01) and sMTU (stiff, − 0.35 ± 0.08 m·s−1; control, − 0.45 ± 0.11 m·s−1; p ≤ 0.001) compared to a control condition. The positive and net work performed at the arch and pMTU, and the net work at the sMTU were significantly lower in the stiff compared to the control condition.ConclusionThe findings of this study showed that if a compliance of the foot-shoe interface is altered during running (e.g. by increasing the MBS of a shoe), the mechanics of other structures change as well. This could potentially affect long-distance running performance.
Highlights
Individual compliances of the foot-shoe interface have been suggested to store and release elastic strain energy via ligamentous and tendinous structures or by increased midsole bending stiffness (MBS), compression stiffness, and resilience of running shoes
The results of this study showed significantly lower shortening velocities of the shank muscle-tendon unit (sMTU) in the stiff compared to the control condition
In support of this hypothesis, the contact times in this data set were significantly increased by ~ 13 ms per step when running in the stiff compared to the control condition, as described previously [5], which represents a 4.76% decrease in rate of force generation
Summary
Individual compliances of the foot-shoe interface have been suggested to store and release elastic strain energy via ligamentous and tendinous structures or by increased midsole bending stiffness (MBS), compression stiffness, and resilience of running shoes. In the stance phase of running, multiple structures (e.g. running shoe, foot arch, tendons, etc.) interact with each other to transmit forces produced by the lower limb muscles through the foot to the ground Some of these structures have been suggested to store and release elastic strain energy via ligamentous and tendinous elements [1,2,3] or by increased midsole bending stiffness (MBS) [4, 5], compression stiffness, or resilience [6] of a running shoe. Because this previous work compared barefoot versus shod running only, it remains unclear if these findings are related to wearing footwear, in general, or to systematic differences in specific footwear features such as the MBS
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