Abstract
BackgroundInter-limb asymmetry above a certain threshold in functional performance indicates increased injury risk in sports. Fatigue has been found to increase bilateral asymmetry in lower-limb jumping performance among high-school and adult athletes, whereas this impact has not been examined in child athletes. This study aimed to examine the effect of fatigue on inter-limb asymmetry in functional performances in elite Taekwondo athletes aged between 9 and 11 years.MethodsPerformance of single-leg jumps, Star Excursion Balance Test (SEBT), and muscle (hamstring and gastrocnemius) flexibility were measured for 13 elite male child Taekwondo athletes (aged 9.85 ± 0.80 years) at both the rested and fatigued states to examine the inter-limb asymmetry. A two-way repeated measures ANOVA was conducted to examine for difference and the interaction between limb (dominant, non-dominant leg) and state (rested, fatigued state) for each test. Paired t test or Wilcoxon signed-rank test was used to compare the asymmetry magnitude at the rested vs. fatigued state for each test, and the variation of performance post fatigue in the dominant vs. non-dominant leg when appropriate.ResultsThe inter-limb asymmetry in triple-hop distance significantly (p = 0.046) increased with fatigue, whereas the asymmetry significantly (p = 0.004) decreased with fatigue in anterior (ANT) reach distance in SEBT. A significant (p = 0.027) limb by state interaction was shown for posterolateral (PL) reach distance in SEBT, wherein a significant (p = 0.005) bilateral difference was only shown at the rested state. The PL reach distance showed a significantly greater decrease (p = 0.028) post fatigue when using the dominant leg for support compared to using the non-dominant leg.ConclusionsFatigue significantly impacts inter-limb asymmetry in jump performances and dynamic balance for child athletes, while the variation of inter-limb asymmetry post fatigue may be different across tests. For the purpose of injury prevention, practitioners should consider assessing the inter-limb asymmetry for children at both the rested and fatigued state and be mindful of the fatigue response of each leg in functional tests.
Highlights
Inter-limb asymmetry is defined as differences in the function or performance between the dominant and non-dominant limb [1]
A significant (F(1,12) = 6.312, p = 0.027, η2 = 0.345) limb by state interaction was shown for the PL direction: the reach distance at the rested state was significantly (p = 0.005, Effect size (ES) = 0.938) greater when establishing the unilateral stance using the dominant leg compared with using the non-dominant leg, while no significant (p > 0.05) difference was shown between the two sides at the fatigued state
As for the fatigue rate, the PL reach distance showed a significantly (p = 0.028, ES = 0.695) greater decrease, and the COM reach distance showed a tendency (p = 0.056) of greater decrease post fatigue when establishing the unilateral stance using the dominant leg compared with using the non-dominant leg
Summary
Inter-limb asymmetry (or bilateral difference, bilateral asymmetry) is defined as differences in the function or performance between the dominant and non-dominant limb [1]. Inter-limb asymmetry may emerge from longterm training in the same sport [2, 3]. There is a growing interest on the topic of inter-limb asymmetry because of its influence on risk for sport injury. The inter-limb asymmetry may potentially place the lower extremities of both sides at a heightened risk of sport injury [4]. Inter-limb asymmetry above a certain threshold in functional performance indicates increased injury risk in sports. Fatigue has been found to increase bilateral asymmetry in lower-limb jumping performance among high-school and adult athletes, whereas this impact has not been examined in child athletes. This study aimed to examine the effect of fatigue on inter-limb asymmetry in functional performances in elite Taekwondo athletes aged between 9 and 11 years
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