Introduction: The abundant degrees of freedom available in movement result in the inherent variations observed in the performance of a repetitive task, i.e., movement variability. Emerging evidence suggests that identification of deviations in gait parameters of pathological vs. healthy runners could advance our current understanding of overuse injury mechanisms in running related injuries. To date the relationship between running biomechanics, variability and injury remains unclear. The purpose of this review was twofold: (1) to examine the impact of musculoskeletal injury on running gait variability; and (2) to identify potentially maladaptive variations in movement variability by identifying any common deviations that occur in injured populations.
Methods: Medline, CINAHL, Embase, Cochrane library and SPORTDiscus databases were searched until February 2022. Studies were eligible for inclusion if they: (a) examined adult participants (≥ 18 years old) with a current or recent history of lower limb or lumbopelvic injury; (b) collected running 3D biomechanics data; (c) compared movement variability data for at least one dependent variable to a control group; and (d) provided a statistical between-group analysis of variability outcomes. Exclusion criteria were neurological conditions that may impact gait or upper body injuries. Due to methodological heterogeneity, a meta-analysis of results was not performed in this review.
Results: Seventeen cross-sectional and retrospective case-control studies were included in the summative synthesis. Significant (p<.05) differences in variability outcomes were identified in 73% of runners with current injury-related symptoms and 43% of runners who were asymptomatic or had recovered from a recent injury, when compared to a control group. The most common deviations in movement variability identified in the injured groups were: (1) high and low knee-ankle/foot coupling variability and (2) low trunk-pelvis coupling variability.
Discussion: The results suggest that runners with current injury symptoms often display altered gait variability compared to runners who are injury-free. Pain and ankle instability may drive the neuromuscular system to explore alternative movement strategies in these runners, to reduce painful input or protect the injury site. Potential maladaptive running gait strategies identified in this review were high/low knee-ankle/foot and low trunk-pelvis coupling variability. Relatively high/low variability is proposed to perpetuate overuse injuries related to running, so these findings are of relevance to clinicians who manage active populations. Further comparison of results was limited due to the diverse underlying theoretical injury models and by the substantial number of biomechanical variables used to measure variability outcomes across the studies.
Impact/Application to the field (can be 1-2 dot points):
- •Runners who continue to run with injury symptoms often employ altered and potentially injurious movement variability strategies when compared to those who are injury-free.
- •Specific maladaptive variables identified in this review can help to direct future researchers investigating the impact of injury on running variability and address the issue of outcome heterogeneity in movement variability research.
Conflict of Interest: This work was financially supported by General Electric and National Basketball Association Orthopedics and Sports Medicine Collaboration (Chicago, USA).