Wednesday, February 10, 2016

"The Foot’s Arch and the Energetics of Human Locomotion"

A weak arch, especially in my weaker foot, has been the main cause of my running woes.  And no, minimalist/barefoot running alone did not fix it.
"...Since the initial study by Ker et al.5 the hypothesis that the foot is an energy-saving spring has never been tested directly during locomotion and it is unknown to what extent the compression, and subsequent storage and return of elastic energy in the foot’s longitudinal arch affects the metabolic cost of locomotion. Here we propose that the metabolic energy saved by the arch spring is a function of the amount of positive mechanical work it supplies passively (non-metabolically) and the cost of performing that work had it instead been done by active muscle requiring metabolic energy.

"We test this hypothesis experimentally using custom-manufactured orthotic insoles designed to restrict arch compression and thus reduce arch elastic work. To test our predictions about the effect of arch strain on locomotor cost, we used orthotic insoles to vary arch strain during walking and running at different inclines and foot strike types (rearfoot strike [RFS] vs forefoot strike [FFS])....

"...Our analyses and model generally support the hypothesis that the arch spring saves metabolic energy by reducing the mechanical work that would otherwise need to be generated by active muscle (Fig. 2). Indeed, the elevated metabolic cost of level running after restricting arch compression near-maximally (~80%, FAI) and by ~60% (HAI) was predicted within 1% and 2.5%, respectively, of the measured values based on the cost of replacing lost elastic arch work with muscular work. The agreement between the modelled and experimental effect on the metabolic cost of level running was remarkably robust across a nearly two-fold difference in arch compression (FAI 10 mm reduction in compression vs HAI 6.5 mm reduction; Fig. 1a), strengthening the interpretation that the elevated metabolic cost results specifically from lost arch elastic energy...."

"...Despite confirming that arch compression is greater in FFS compared with RFS runners in the minimal shoe only level run (p = 0.022; Table 1), our hypothesis that forefoot runners would be more affected by restricting arch compression was not supported....
Really interesting stuff.

via Ben Greenfield