Short communicationChanges in timing of muscle contractions and running economy with altered stride pattern during running
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.
Section snippets
Participants
Eleven male trained runners participated in this study. Their mean (SD) age was 26.4 (7.1) years, height was 179.1 (6.7) cm, body mass was 68.5 (8.3) kg, and personal best 10 km time was 34.81 (3.12) min. The study was approved by the university ethics committee. All participants were informed of the purposes and procedures, and signed an informed consent form.
Procedures
Participants visited the laboratory on two occasions separated by at least 48 h. Running was performed on the same treadmill (h/p/cosmos,
Results
Stride length test–retest ICC (95% CI) between visit 1 and NAT during visit 2 was 0.93 (0.76–0.98) with no significant difference between visits, which suggests a reliable foot contact method. In addition, stride length SEM was 0.03 m. There were no significant differences between any of the PREF and NAT outcome variables (p > 0.05) during visit 2 indicating that synchronising foot contacts with a metronome signal produced a natural treadmill running technique.
The greatest running economy was
Discussion
In agreement with previous research our sample of runners preferred a stride which was longer than the optimum, as derived from a quadratic curve which was fit through the running economy data [1]. The curve was relatively flat around the optimum and this could explain why we detected no significant difference in running economy with shorter strides. These results suggest that runners who exhibit preferred strides that are longer than the most economical can optimise running economy and reduce
Conflict of interest statement
The authors have no conflicts of interest.
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