Exploring running-style modulation

Technological advances in the past decades allow runners to measure a large range of variables by means of wearables and smartphone applications. However, the interpretation of such variables is often lacking. In this thesis, I present a series of foundational studies to implement the concept of guided running-style exploration in the actual training of running. For the development of a successful application based on this concept, three things are required: an appropriate conceptual framework, an accurate measurement system, and effective instructions. The conceptual framework I chose is the dual-axis model, which states that the running style at a certain speed can be described by means of the cadence and duty factor (relative stance time). Thus, cadence, duty factor, and speed are the running variables of interest. For the measurement system, I analysed the test-retest reliability, face validity and concurrent validity of the cadence and stance time derived from instrumented wireless earbuds and found them to be good. This implies that the wireless instrumented earbuds can be used as a valid and reliable measurement system for runners. The core of this thesis is researching effective instructions to modulate cadence and duty factor. For the cadence, acoustic pacing can be a feasible instruction method. Acoustic pacing can be step-based (i.e. a cue for each step) or stride-based (i.e. a cue for every other step), these two forms were compared in terms of effectiveness and their effect on impact forces. Step-based pacing led to more stable auditory-motor coordination than stride-based pacing in both walking and running. There was no effect of the presence of the acoustic pacing on the impact forces. Therefore, acoustic step-based pacing can be used to modulate cadence with the underlying aim of reducing impact forces, without introducing a counterproductive effect. For the duty factor, I tested four verbal instructions: increase or decrease stance time and increase or decrease flight time. Results showed that the participants were able to modulate duty factor without changing cadence. There was no difference between the different instructions, indicating that either type of instruction can be used to modulate the duty factor. When provided separately in overground running, the acoustic pacing and verbal instructions did lead to covarying effects, especially on speed. However, when the acoustic pacing and verbal instructions were combined for running-style modulation according to the dual-axis model, the covarying effects on speed were mitigated. The combined instructions can thus effectively be used for running-style modulation according to the dual-axis model in overground running. In collaboration with the company Dopple, the newly established instructions were implemented in the Running Buddy application for guided running-style exploration. This application is a good first step towards guided running-style exploration, but improvements can still be made, especially in terms of user autonomy. Overall this thesis provides a base for the necessary steps towards guided running-style exploration. With guided running-style exploration, runners can in the future actively vary their running style to reach their personal goals in terms of performance and injury risk.