Is passive metatarsophalangeal joint stiffness related to leg stiffness, vertical stiffness and running economy during sub-maximal running?

This study examined whether passive metatarsophalangeal joints (MPJ) stiffness was associated with leg stiffness (K-ieg) vertical stiffness (K-vert) and running economy (RE) during sub-maximal running. Nine male experienced runners underwent passive MPJ stiffness measurements in standing and sitting positions followed by sub-maximal running on an instrumented treadmill. With the individual foot position properly aligned, the MPJ passive stiffness in both sitting (MPJ(sit)) and standing positions (MPJ(stand)) were measured with a computerized dynamometer. Data were collected at a running speed of 2.78 m/s, representing a stabilized level of energy expenditure. Pedar pressure insole was used to determine the contact time (t(c)) and peak reaction force for the calculation of K-ieg and K-vert. A respiratory gas analysis system was used to estimate the RE. Bivariate correlation test was performed to examine the correlation among MPJ stiffness, contact time, K-ieg, K-vert, and RE. The results showed that MPJ(sit) and MPJ(stand) were inversely correlated with RE (p = 0.04, r = -0.68 to -0.69), suggesting that stiffer MPJ improves RE. In addition, MPJ(sit) was correlated positively with K-ieg (p < 0.01, r = 0.87), K-vert (p = 0.03, r = 0.70) but inversely with t(c) (p = 0.02, r = -0.76), while MPJ(stand) was correlated positively with the K-vert (p = 0.02, r = 0.77). These findings suggested that strength of toe plantar flexors provides stability and agility in the stance phase for more effective and faster forward movement. (C) 2016 Elsevier B.V. All rights reserved.