sensors Article Evaluation of Accelerometer-Derived Data in the Context of Cycling Cadence and Saddle Height Changes in Triathlon Stuart A. Evans 1,*, Daniel A. James 1, David Rowlands 2 and James B. Lee 1 1 SABEL Labs, College of Health and Human Science, Charles Darwin University, 0810 Darwin, Australia; [email protected] (D.A.J.); [email protected] (J.B.L.) 2 School of Engineering, Griffith University, 4111 Nathan, Australia; d.rowlands@griffith.edu.au * Correspondence: [email protected] Abstract: In the multisport of triathlon cycling is the longest of the three sequential disciplines. Triathlon bicycles differ from road bicycles with steeper seat tube angles with a change to saddle height altering the seat tube angle. This study evaluated the effectiveness of a tri axial accelerometer to determine acceleration magnitudes of the trunk in outdoor cycling in two saddle positions. Interpretation of data was evaluated based on cadence changes whilst triathletes cycled in an aerodynamic position in two saddle positions. The evaluation of accelerometer derived data within a characteristic overground setting suggests a significant reduction in mediolateral acceleration of the trunk, yielding a 25.1% decrease when saddle height was altered alongside reduced rate of perceived exertion (3.9%). Minimal differences were observed in anteroposterior and longitudinal acceleration. Evaluation of sensor data revealed a polynomial expression of the subtle changes between both saddle positions. This study shows that a triaxial accelerometer has capability to continuously measure acceleration magnitude of trunk movements during an in-the-field, varied cadence cycle protocol. Accessible and practical sensor technology could be relevant for postural considerations when exploring saddle position in dynamic settings. Citation: Evans, S.A.; James, D.A.; Rowlands, D.; Lee, J.B. Evaluation of Keywords: accelerometer; sensor; centre of mass; cycling; sports science Accelerometer-Derived Data in the Context of Cycling Cadence and Saddle Height Changes in Triathlon. Sensors 2021, 21, 871. https:// 1. Introduction doi.org/10.3390/s21030871 Triathlon is an endurance multisport race consisting of swimming, cycling and running over various distances. Regardless of race distance, triathletes compete for fastest overall Academic Editor: Basilio Pueo completion time, racing each segment sequentially. Irrespective of individual disciplines, Received: 11 December 2020 cycling takes up the most time in triathlon. Accepted: 24 January 2021 Published: 28 January 2021 Bicycles designed for triathlon tend to differ from the ones used by road cyclists [1] as triathletes seek improvements in their aerodynamic profile by reducing their frontal Publisher’s Note: MDPI stays neutral projected area [2]. This is achieved by moving the saddle further forward relative to the with regard to jurisdictional claims in bottom bracket compared to road cyclists [3] while placing the trunk further downwards published maps and institutional affil- that permit the forearms to extend onto integrated aerodynamic bars. iations. Saddle height is one aspect of bike setup that can affect both performance and in- jury [4,5]. For instance, bicycle saddle configuration dictates muscle activation [3], joint kinematics [6], and performance [4]. As saddle height modifies the mechanical work of the lower limb joints [7], alterations to saddle height will alter trunk position with performance implications. Nonetheless, triathletes often select the saddle position relative to the pedals Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. (and therefore crank) by comfort rather than scientific knowledge. As sports medicine This article is an open access article practitioners need to be able to advise athletes on ways to improve cycling performance, distributed under the terms and an understanding of how saddle height can influence trunk motion and the effects on conditions of the Creative Commons performance are important. Attribution (CC BY) license (https:// The evaluation of kinematics in functional, sports-specific situations continues to creativecommons.org/licenses/by/ receive attention [8]. Trunk position has been identified as an important parameter that 4.0/). can affect cycling performance. For instance, upper body position has been related to Sensors 2021, 21, 871. https://doi.org/10.3390/s21030871 https://www.mdpi.com/journal/sensors Sensors 2021, 21, x FOR PEER REVIEW 2 of 13 Sensors 2021, 21, 871 2 of 13 affect cycling performance. For instance, upper body position has been related to changes in activation of lower limb muscles [9], shown to effect cycling performance [10]. In this regard, kinematic parameters like velocity and acceleration can be used to quantify move- changesment related in activation to trunk position of lower when limb musclescycling in [9 ],motion. shown Measurement to effect cycling of trunk performance acceleration [10]. Incould this yield regard, more kinematic specific parameters information like about velocity the andrelationship acceleration to revolutions can be used per to quantify minute movement related to trunk position when cycling in motion. Measurement of trunk (rev/min1, cadence) and upper body postural movement. acceleration could yield more specific information about the relationship to revolutions per Past results have reinforced that feedforward postural responses result in trunk minute (rev/min1, cadence) and upper body postural movement. movements with trunk orientation and centre of mass (CoM) both controlled relative to Past results have reinforced that feedforward postural responses result in trunk move- rapid limb movements [11]. Notably, phasic activation of superficial trunk muscles was ments with trunk orientation and centre of mass (CoM) both controlled relative to rapid consistent with that of preparatory motion with the direction of CoM motion. Similarly, limb movements [11]. Notably, phasic activation of superficial trunk muscles was con- Savelberg et al. [9] reported that trunk position influences EMG patterns. However, the sistent with that of preparatory motion with the direction of CoM motion. Similarly, tested positions (i.e., 20° forward and backward of the vertical) were not comparable to Savelberg et al. [9] reported that trunk position influences EMG patterns. However, the the aerodynamic position used by triathletes. Furthermore, magnitude of acceleration was tested positions (i.e., 20◦ forward and backward of the vertical) were not comparable to the not measured. A low level of core trunk muscle strength or stability can cause additional aerodynamic position used by triathletes. 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