Abstract
Musculoskeletal overuse injuries represent a significant health burden for athletes and a puzzling rehabilitation pathway for clinicians. The complex pathophysiology of overuse injuries impedes their accurate identification and limits the advancement of injury prevention methods. Current methods used to screen for overuse injury risk do not account for the evolving, non-linear progression of somatic tissue injury to repair. There is a demonstrated need for a monitoring method that can assess a tissue’s response to / capacity for loading. One potential monitoring method involves the autonomic nervous system (ANS); a system responsible for regulation of inflammatory pathways during tissue pathology and regeneration. Cardiac ANS activity can be measured indirectly with heart rate variability (HRV). This thesis investigated the association between changes in ANS activity, indexed by HRV, and the development of overuse injuries.
Methods: This thesis involved four processes: development of the research question and theoretical framework, a systematic review, a reliability study, and a cohort study. A literature review was performed to summarize findings on HRV monitoring in sport and evaluate possible mechanisms for ANS participation in overuse injury pathophysiology. A systematic review examined the evidence base for HRV monitoring and overuse injuries. To determine optimal study protocol procedures for improved inter-session reliability of HRV, a reliability study (n = 41) was completed. In the testing phase, a field-based cohort study (n = 29) was conducted to explore the association between changes in HRV leading up to development of overuse injuries in college-aged participants.
Results: Evidence from the literature review suggested that the ANS is responsible for local inflammatory responses that occur during tissue pathology. Based on this, a theoretical framework was created that hypothesized the relationship between ANS activity and overuse injury. The systematic review confirmed the absence of literature investigating HRV and overuse injury, and provided preliminary evidence for an association between HRV and acute musculoskeletal injury. The reliability study demonstrated that inter-session consistency of HRV was improved with collection of five daily HRV measures per week, application of “low” artefact filtering, and analysis of time domain HRV measures. Results from this study informed the data collection and processing procedures of the cohort study. Linear mixed model analyses for the cohort study (n = 29) found no statistically significant associations between changes in HRV and overuse injury problems.
Conclusions: This thesis produced a novel hypothesis for exploring the role of ANS monitoring for early detection of developing musculoskeletal overuse injury. Testing the hypothesis did not produce statistically significant associations between HRV and overuse problems. Despite these findings, the cohort study adds to the existing evidence for HRV monitoring in college-aged participants. The work of this thesis represents a step towards improved understanding of the behavior of overuse injury pathophysiology through monitoring patterns of change in a global, dynamic system involved in tissue injury and repair. Finally, this thesis highlighted the need for future research that incorporates broader, integrative approaches to investigate how complex interactions among risk factors contributes to the emergence of overuse injury.