Barefoot-shod running differences: shoe or mass effect?

The higher oxygen consumption reported when shod running is compared to barefoot running has been attributed to the additional mass of the shoe. However, it has been reported that wearing shoes also modified the running pattern. The aim of this study was to distinguish the mass and shoe effects on the mechanics and energetics when shod running. Twelve trained subjects ran on a 3-D treadmill ergometer at 3.61 m . s (-1) in six conditions: barefoot, using ultra thin diving socks unloaded, loaded with 150 g, loaded with 350 g, and two shoe conditions, one weighing 150 g and another 350 g. The results show that there was a significant mass effect but no shoe effect for oxygen consumption. Stride frequency, anterior-posterior impulse, vertical stiffness, leg stiffness, and mechanical work were significantly higher in barefoot condition compared to shod. Net efficiency, which has metabolic and mechanical components, decreased in the shod condition. The mechanical modifications of running showed that the main role of the shoe was to attenuate the foot-ground impact by adding damping material. However, these changes may lead to a decrease of the storage and restitution of elastic energy capacity which could explain the lower net efficiency reported in shod running.

Mechanical comparison of barefoot and shod running.

In order to further compare shod versus barefoot running, 35 subjects ran two bouts of 4 minutes at 3.33 m x s(-1) on a treadmill dynamometer. Parameters were measured on about 60 consecutive steps. Barefoot showed mainly lower contact and flight time (p < 0.05), lower passive peak (1.48 versus 1.70 body weight, p < 0.05), higher braking and pushing impulses (p < 0.05), and higher pre-activation of triceps surae muscles (p < 0.05) than shod. It was concluded that when performed on a sufficient number of steps, barefoot running leads to a reduction of impact peak in order to reduce the high mechanical stress occurring during repetitive steps. This neural-mechanical adaptation could also enhance the storage and restitution of elastic energy at ankle extensors level.