Abstract
Minimizing between-limb asymmetries during running is often a goal of training, as increased asymmetries are related to decreased efficiency and increased energy expenditure. However, it is unknown if asymmetries change with increased running exposure or are related to actual race performance. The purpose of this study was to determine (1) if pre-season asymmetries changed year-to-year among collegiate cross country runners, and (2) if these asymmetries were associated with within-season personal records (PRs). Pre-season biomechanical test results and race performance data were analyzed for 54 unique runners (28 female) across six seasons, totaling 152 assessments (age: 19.1 (0.9) years, height: 1.71 (0.10) m, weight: 61.7 (7.7) kg (values = mean [standard deviation])). Biomechanical asymmetries included ground reaction forces; ground contact time; base of gait; foot inclination angle; and peak hip flexion, hip extension, hip adduction, pelvic drop, knee flexion, and ankle dorsiflexion. Year of collegiate eligibility was used to quantify training exposure. Asymmetries during running did not change across years of eligibility (p ≥ 0.12), except propulsive impulse, which decreased over time (p = 0.03). PR times were faster with decreased propulsive impulse asymmetry and increased AVLR and peak ankle dorsiflexion asymmetries. This is the first study to assess longitudinal asymmetries over time and provide potential targets for interventions aimed at modifying asymmetries to improve performance.
Highlights
Running mechanics and between-limb asymmetries are often assessed by clinicians and coaches to gain insight into an individual’s running performance potential [1,2,3].The mechanics of a healthy runner are presumed to be symmetrical [4]; some level of asymmetry is common among healthy runners, with the level of asymmetry varying considerably depending on the metric of interest [5,6]
While year-to-year changes in propulsive impulse asymmetry were not statistically significant, propulsive impulse asymmetry showed a trend towards decreasing over time (Table 3), with 7.4% asymmetry observed in the first year of eligibility and 3.1% asymmetry observed in the fifth year of eligibility
While the present study does not support causal inferences regarding the relationship between propulsive impulse asymmetries and race performance, our findings suggest that symmetrical propulsive impulse, in addition to greater overall propulsive impulse in accordance with prior work, may be beneficial for improving race personal records (PRs)
Summary
Running mechanics and between-limb asymmetries are often assessed by clinicians and coaches to gain insight into an individual’s running performance potential [1,2,3].The mechanics of a healthy runner are presumed to be symmetrical [4]; some level of asymmetry is common among healthy runners, with the level of asymmetry varying considerably depending on the metric of interest [5,6]. Running mechanics and between-limb asymmetries are often assessed by clinicians and coaches to gain insight into an individual’s running performance potential [1,2,3]. Minimizing between-limb asymmetry during running is often a goal of training, as increased asymmetry is thought to be related to decreased performance. Increased asymmetry was correlated with decreased mechanical efficiency (r = 0.66) during a 10 km run in amateur trained runners [7]. Among active individuals, a 10% increase in step time asymmetry and average vertical ground reaction force asymmetry resulted in a 3.5%. Increases in asymmetry result in decreased mechanical efficiency and increased metabolic power, it is unknown if increased asymmetries translate to increased race times (e.g., worse performance)
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