Mechanical modifications to increased step frequency while running freely outside.

Abstract

Increasing step frequency while running in laboratory environments has been shown to alter running mechanics, such as decreasing impacts with the ground. Increasing step frequency may be suggested by running specialists because these mechanical changes correlate to reduced injury risk. The purpose of this study was to determine if runners, running outside in a control free environment, exhibit similar changes in mechanics to previous research. Twenty individuals (10 male, 10 female) who run for health, training or competition were recruited to participate in this project; however, only 8 accomplished the task of matching the specified step frequency. Runners were fitted with a RunScribe® system consisting of 3 IMU pods (one for each foot and one on the sacrum) from which several variables were recorded, such as Step Length, Impact Gs, and stiffness variables. They initially ran 5 times each on a flat (~300 m) and on an 8-10% incline (~100 m) straight path at their preferred running speed. For each surface, their average step frequency was determined, and a metronome was set to +5% of their average. They then ran to the metronome 5 times each on the two courses. While running on the flat surface, contact time (-11.5%), speed (+13.8%), impact Gs (+9.8%) and vertical stiffness (+13.6%) significantly different (P>0.05) with increased step frequency. While running on the incline surface, contact time (-7.7%) and vertical stiffness (+14.6%) significantly changed (P>0.05) with increased step frequency. This research shows that in a free running environment, runners will increase their step length as they increase their step frequency, which does not lead to a decrease in ground impact, as has been shown in previous research where speed was controlled.