Changes in timing of muscle contractions and running economy with altered stride pattern during running

Highlights

• The effect of altered stride pattern on running economy and muscle coordination.

• Identified timing of muscle activation and eccentric contractions during running.

• A quadratic fit to economy data was optimised at a shorter than preferred stride.

• Timing of muscle contractions changed at shorter than preferred strides.

• We detected no changes to the timing of muscle contractions with longer strides.

Abstract

Large alterations to the preferred running stride decrease running economy, and shorter strides increase leg muscle activity. However, the effect of altered strides on the timing of leg muscle activation is not known. The aim of this study was to evaluate the impact of moderate alterations to the running stride on running economy and the timing of biceps femoris (BF), vastus lateralis (VL) and gastrocnemius (GAST) muscle contractions. The preferred stride pattern for eleven trained male runners was measured prior to a separate visit where participants ran for bouts of 5 min whilst synchronising foot contacts to a metronome signal which was tuned to (1) the preferred stride, and (2) frequencies which related to ±8% and ±4% of the preferred stride length. Running economy was measured at each stride pattern along with electromyography and three-dimensional kinematics to estimate onset and offset of muscle contractions for each muscle. Running economy was greatest at the preferred stride length. However, a quadratic fit to the data was optimised at a stride which was 2.9% shorter than preferred. Onset and offset of BF and VL muscle contractions occurred earlier with shorter than preferred strides. We detected no changes to the timing of muscle contractions with longer than preferred strides and no changes to GAST muscle contractions. The results suggest that runners optimise running economy with a stride length that is close to, but shorter than, the preferred stride, and that timing of BF and VL muscle contractions change with shorter than preferred strides.

Introduction

Lengthening or shortening the preferred running stride produces a U-shaped running economy response. Although runners maximise economy close to the preferred stride, the optimum stride is generally shorter than preferred which creates a flat portion of the curve [1]. These findings suggest that small stride alterations can be tolerated and, in some cases, are encouraged to optimise running economy. However, with the exception of one study [2], previous research has investigated the effect of large (>10%) stride alterations on running economy [1].

Whilst shorter than preferred strides are associated with increased leg muscle activation and reduced hip and knee joint loads [3], [4], the changes in timing of leg muscle activation with altered stride patterns are not known. According to a constant electromechanical delay, muscle contractions should consistently occur earlier or later with more or less frequent strides so that forces are produced over the same portion of the stride [5]. However, during cycling the onset and offset of muscle contractions with altered movement frequency are muscle-specific [6], and it is not known if this is the case for running.

The aim of this study was to evaluate the effect of moderate stride alterations on running economy and the onset and offset of biceps femoris (BF), vastus lateralis (VL) and gastrocnemius (GAST) muscle contractions.