# The Effect of Neuromuscular Fatigue on the Spatiotemporal Coordination of Rowing
###### Abstract  
Within rowing, lower back disorders (LBDs) are common, but the mechanisms underpinning LBDs are poorly understood. Considering this, it is essential to understand how coordination and motor control change under different constraints such as ergometer rowing and fatigue. This can help better inform movement features linked to LBDs. Measurement of the continuous relative phase (CRP) is a method used to quantify body segment and joint coordination, as CRP measures the spatiotemporal control of multi-joint movement. The purpose of this study was twofold: to examine the general spatiotemporal coordination aspects of ergometer rowing in an unfatigued state, and to quantify how the spatiotemporal coordination of a rowing movement changes in response to a fatigue-inducing rowing trial. Wearable IMUs monitored 20 participants' movement during a 200 m ergometer row. The Borg-10 Rating of Perceived Exertion (RPE) scale was used to quantify perceived fatigue. Despite significant RPE increases across all athletes, the spatiotemporal coordination of rowing revealed prevailing strategies for the lumbar spine and lower extremity but no significant effects (\(\alpha\) = 0.05) of fatigue on CRP outcomes (MARP, DP), cross-correlation lag (R\({}_{\text{XY}}\)), or range of motion. These findings provide further insight into rowing movements and support the idea that heterogeneous responses to fatigue may exist, requiring further study. l 20242  
gold-standard laboratory-based motion capture systems, further supporting their use in various settings [6; 7]. Within the sport of rowing, LBDs are extremely common [3; 8]. However, to this point, the specific risk factors for the development of LBDs in rowing athletes are unclear [9]. Previous work has quantified the kinematic and electrophysiological demands during a typical rowing stroke [10]. Specifically, [PERSON] and colleagues (2009) noted that the axial structures, such as the spine, are particularly vulnerable to injury during the early drive phase. This is due to the spine being loaded with a compressive force typically 4.6 times the rower's body weight, all while in a flexed position, with these loads typically occurring 230-260 times during a single 2000 m race [10]. The cumulative microtrauma imposed by these repetitive stresses has the potential to result in mechanical injury to the passive tissues supporting the spinal column (e.g., intervertebral discs) [11], as well as the muscles surrounding the spine (e.g., transversospinales, paraspinals), thereby contributing to the high prevalence of LBDs reported in rowing athletes [10]. In addition to this, recent work has suggested that rowing-induced fatigue has the capacity to affect spine posture, resulting in enhanced forward flexion of the thoracic spine during fatigue, thereby exaggerating the mechanical loads placed on axial structures [12]. What has yet to be assessed in the context of rowing-specific movements is how neuromuscular fatigue affects the coordination between the multiple joints required to complete a rowing movement. Specifically, if fatigue results in reduced coordinative variability, as this may accelerate overuse injuries in rowing athletes due to increased cumulative loading of specific anatomical structures during a rowing bout or prolonged periods of training [13]. One method to quantify body segment and joint coordination is through the estimation of the continuous relative phase (CRP) [13]. CRP angles are obtained through the phase portraits, generated from the measured time-series (i.e., joint or segment angle) and the first time derivative (i.e., joint or segment angular velocity) [13]. CRP values derived from a phase portrait provide an understanding of the spatiotemporal sequencing of multiple segments and/or joints and are often represented as measures of the mean absolute relative phase (MARP) and deviation phase (DP) [14].