Forefoot stiffness. It’s all in the supination…

Remember a month ago when we talked about the basics of gait? If not, please see posts the week of 6/27 for a in depth discussion

Suffice it to say, in stance phase (about 60% of the walking and 40% of the running gait cycles) we have 2 motions occurring: pronation and supination. In pronation (which begins as soon as the foot hits the ground and should end at midstance) the foot is becoming a mobile adaptor, so it can adapt to irregular surfaces and act as a shock absorber. 

In supination (which begins at midstance and ends at preswing) the foot is becoming a rigid lever, to assist in transferring muscular forces to the lower limb to propel us forward.

The picture above shows supination nicely. Remember that when one foot is in midstance, the opposite leg (in swing phase) assists in supination.

This study (IOHO) demonstrates the principle of supination nicely and demonstrates the (major) role the foot plays in forefoot stiffness.

J Biomech. 2005 Sep;38(9):1886-94. A comparison of forefoot stiffness in running and running shoe bending stiffness. Oleson M, Adler D, Goldsmith P. Source http://www.ncbi.nlm.nih.gov/pubmed/16023477

Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Drive, N.W. Calgary, Alberta, Canada T2N 1N4.

Abstract

This study characterizes the stiffness of the human forefoot during running. The forefoot stiffness, defined as the ratio of ground reaction moment to angular deflection of the metatarsophalangeal joint, is measured for subjects running barefoot. The joint deflection is obtained from video data, while the ground reaction moment is obtained from force plate and video data. The experiments show that during push-off, the forefoot stiffness rises sharply and then decreases steadily, showing that the forefoot behaves not as a simple spring, but rather as an active mechanism that exhibits a highly time-dependent stiffness. The forefoot stiffness is compared with the bending stiffness of running shoes. For each of four shoes tested, the shoe stiffness is relatively constant and generally much lower than the mean human forefoot stiffness. Since forefoot stiffness and shoe bending stiffness act in parallel (i.e., are additive), the total forefoot stiffness of the shod foot is dominated by that of the human foot.

The Geeks of Gait: Ivo and Shawn