Advancing methods and detecting meaningful change in coordination variability measures used in sports biomechanics

  • Holly Stock

Student thesis: Doctoral ThesisPhD


Coordination variability measures have become popular within sports biomechanics for studying topics such as learning, expertise and injury. Research in these areas has suggested that coordination variability can enhance learning, be characteristic of expert skill levels and that excessively high or low variability may be a risk factor for injury.
Coordination variability measures in kinematic analyses have now been in use for over twenty years in sports biomechanics literature. A subset of kinematic coordination variability measures calculate the variability of vectors (which are formed between consecutive data points on an angle-angle diagram) and has therefore been termed ‘vector coding’. This programme of research investigates two methodological considerations associated with vector coding variability measures. First, a combined simulated and experimental approach demonstrates a statistical artefact stemming from the use of circular statistics that can cause steep increases in coordination variability at times when very little movement occurs in the joints or segments, between which coordination is being measured. An alternative method for calculating coordination variability based on the calculation of ellipse areas is presented that is shown not to be affected by the artefact. Second, a further modification to the ellipse area method is proposed that uses angular velocities to represent angular dynamics. This contrasts with traditional vector coding techniques that use the change in angle between consecutive normalised time points. The use of angular velocities is suggested to align the vector coding methods with biomechanical conventions and retain more temporal information compared to the traditional method.
Very little research has detailed the repeatability of coordination variability measures and what magnitude of change might be methodologically or clinically meaningful. This programme of research therefore also investigates the repeatability of the ellipse area, angular velocity-based measure of coordination variability (the velocity ellipse method) proposed in the thesis. Two repeatability studies (of running gait and a 45 degree cutting manoeuvre) provided data to calculate what magnitude of change is methodologically meaningful for the velocity ellipse method. Experimental data is also presented investigating scenarios where differences in coordination variability might be expected to occur. Specifically 1) in an individual who transitioned from a healthy state to one where running was painful and 2) between a population of individuals who had had an ACL reconstruction compared to a healthy population performing a 45 degree cutting manoeuvre before and after an acute fatigue intervention. Minimum detectable changes estimated from the repeatability data aided the interpretation of the experimental data. No differences were observed were greater than the minimum detectable changes in 1) the longitudinal changes as the case study participant transitioned to painful running, 2) cutting manoeuvres before and after a fatiguing protocol or 3) coordination variability between athletes who had had ACL reconstructions compared to a healthy control group. This could either suggest that the repeatability of the measure is too low to be able to detect clinically meaningful changes, or that injury and fatigue may not consistently induce meaningful changes in coordination variability measures. Limitations of the velocity ellipse method are discussed, and suggestions are made that may increase the repeatability and thus improve its ability to detect clinically meaningful differences in future research studies.
Date of Award17 Feb 2021
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorEzio Preatoni (Supervisor), Cassie Wilson (Supervisor), Richard van Emmerik (Supervisor) & Chris McLeod (Supervisor)

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