(12) STABILITY OF RUNNING STRIDE ASYMMETRIES ACROSS MULTIPLE INTENSITIES AND THEIR RELATIONSHIP TO JUMP ASYMMETRY IN WELL-TRAINED RUNNERS

Purpose: Running asymmetries, such as left-right inter-limb differences in ground contact time (GCT) and ground reaction force (GRF), are commonly observed in runners. Although they are typically small (~2-5%), subtle imbalances can have practical implications(2). Larger asymmetries have been linked to poorer running economy, which may negatively impact performance(3). If asymmetries are amplified at higher intensities, they may translate to decreased running efficiency under demanding conditions. Determining if similar asymmetries are present in running and countermovement jump (CMJ) tasks can reveal whether the imbalance is present across both unilateral and bilateral dynamic movements. The purpose of this study was to assess GCT and GRF at three running speeds and their relationships to asymmetries in CMJ impulse, peak force, and rate of force development (RFD) at 200ms. Methods: Stride parameters were assessed via a validated 2D video app(1) in well-trained runners (N=16, age=34.6±5.7y, height=171.7±9.4cm, mass=66.5±11.5kg, VO₂max=58.8±5.6 ml·kg⁻¹·min⁻¹, 10 males, 6 females) as they ran on a treadmill at 3 individualized speeds based on recent race performance: warm-up (slow), easy aerobic (medium), and half-marathon (fast) pace. On a separate day, CMJ tests were completed on force plates. Results: A 1x3 ANOVA revealed no significant differences in GCT and GRF asymmetry across the three running speeds. For GCT and GRF asymmetry, no difference was found between slow vs. medium (t=1.19, p=0.753, t=0.166, p=0.87), slow vs. fast (t=1.78, p=0.287, t=-0.771, p=0.453), or medium vs. fast (t=0.476, p=0.641, t=-1.19, p=0.252) pacing. Correlation analysis found strong associations among asymmetries within the same movement type but limited relationships between running and jumping asymmetries. GCT asymmetry was moderately to strongly correlated between all paces (r=0.73-0.82, p< 0.001), indicating stability across intensities. GRF asymmetry showed a moderate correlation between medium and fast pace (r=0.65, p=0.005). Concentric impulse asymmetry was strongly associated with concentric peak force asymmetry (r=0.88, p< 0.001) and force at peak power asymmetry (r=0.92, p< 0.001). Conclusions: Asymmetries in GCT and GRF remained stable across paces in well-trained competitive runners, suggesting that ingrained movement patterns are maintained regardless of intensity and increasing oxygen cost, possibly due to neuromuscular control mechanisms. The absence of strong correlations between running and CMJ asymmetries indicates that inter-limb imbalances are task-specific. It is possible that runners compensate for strength deficits through neuromuscular adaptations or that the bilateral nature of jumping tasks inherently differs in motor control demands from unilateral propulsion in running. Practical Applications: Running asymmetries are not solely a function of unilateral strength imbalances but reflect complex coordination patterns unique to cyclic locomotor tasks. Asymmetries in performance tests do not directly translate to running gait asymmetries, emphasizing the importance of task-specific assessments when evaluating an athlete’s biomechanics. Therefore, interventions aimed at reducing unilateral strength imbalances may not necessarily alter running asymmetry. Still, future research may consider monitoring asymmetries under fatigue or sprint conditions, which may provide better insights into performance optimization. Acknowledgements: None.