Abstract
Motor control in swimming can be analyzed using low- and high-order parameters of behavior. Low-order parameters generally refer to the superficial aspects of movement (i.e., position, velocity, acceleration), whereas high-order parameters capture the dynamics of movement coordination. To assess human aquatic behavior, both types have usually been investigated with multi-camera systems, as they offer high three-dimensional spatial accuracy. Research in ecological dynamics has shown that movement system variability can be viewed as a functional property of skilled performers, helping them adapt their movements to the surrounding constraints. Yet to determine the variability of swimming behavior, a large number of stroke cycles (i.e., inter-cyclic variability) has to be analyzed, which is impossible with camera-based systems as they simply record behaviors over restricted volumes of water. Inertial measurement units (IMUs) were designed to explore the parameters and variability of coordination dynamics. These light, transportable and easy-to-use devices offer new perspectives for swimming research because they can record low- to high-order behavioral parameters over long periods. We first review how the low-order behavioral parameters (i.e., speed, stroke length, stroke rate) of human aquatic locomotion and their variability can be assessed using IMUs. We then review the way high-order parameters are assessed and the adaptive role of movement and coordination variability in swimming. We give special focus to the circumstances in which determining the variability between stroke cycles provides insight into how behavior oscillates between stable and flexible states to functionally respond to environmental and task constraints. The last section of the review is dedicated to practical recommendations for coaches on using IMUs to monitor swimming performance. We therefore highlight the need for rigor in dealing with these sensors appropriately in water. We explain the fundamental and mandatory steps to follow for accurate results with IMUs, from data acquisition (e.g., waterproofing procedures) to interpretation (e.g., drift correction).
Highlights
Research on human swimming has been extensive in part because of one of the unique properties of water: its high density, which causes great resistance to movement
Motor control investigations follow the principles of coordination dynamics within the theoretical framework of ecological dynamics (Seifert et al, 2013; Davids et al, 2015), an approach used to study the continuous interactions between an individual and his/her environment
Adaptability refers to the subtle blend of behavioral stability and flexibility, in the sense that stability is the robustness of behavior under conditions of perturbation and flexibility is the superficial refinement of behaviors to adjust to constraints (Seifert et al, 2014e)
Summary
Research on human swimming has been extensive in part because of one of the unique properties of water: its high density, which causes great resistance to movement. Determining the upper and lower limb oscillations offers insights into the strategies that swimmers use to create propulsion (it is generally considered that the upper limbs create nearly 90% of the total body propulsion; Deschodt et al, 1999), which can be approached by measuring their instantaneous velocity To compute this velocity, which is considered the best parameter for estimating swimming performance (Barbosa et al, 2011; Dadashi et al, 2015), a supplementary level of analysis is needed, since velocity is not directly obtained from accelerometer or IMUs recordings. This work must be viewed as the first step in automatically detecting the stroke phases of TABLE 1 | Studies focusing on the temporal low-order parameters of swimming behavior
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