Enhanced concentric torque after eccentric loading is a positive contributor to dynamic balance in children

Research Objectives: To investigate if concentric torque is enhanced after eccentric loading at different velocities at the knee and ankle, and whether the enhanced concentric torques are related to dynamic balance in children.

Design: Cross-sectional study.

Setting: University laboratory.

Participants: Children (n=15; 40% male) ages 8-13 years (mean±SD=11.1±1.4 years)

Interventions: Not applicable.

Main Outcome Measures: We used FSST (rapid stepping while changing directions) to determine dynamic balance. A greater time taken to complete FSST indicates poor dynamic balance. Eccentric (ECC), concentric (CONC), and eccentric preloaded concentric (ECCCONC) muscle torque at the knee and ankle were assessed in a random order using the Biodex3 system at two velocities (120° and 180°/second). All torque measures were normalized for weight. Joint-specific enhanced concentric torque was calculated by subtracting CON from ECCCONC torque for each velocity.

Results: Joint-specific enhanced concentric torque after eccentric loading was observed at the ankle at both 120° and 180°/second (p < 0.01 for both) and at the knee at 120°/second (p < 0.01). Enhanced concentric torque at the ankle at 120°/second was negatively related to FSST (rspearman=-0.65, p=0.01). In separate partial correlation models, this relationship remained after controlling for age (rpartial=-0.81, p< 0.01), sex (rpartial=-0.73, p< 0.01), height (rpartial=-0.78, p< 0.01), and muscle strength of the knee (rpartial=-0.76, p< 0.01) and ankle (rpartial=-0.65, p=0.02).

Conclusions: Our study provides novel preliminary evidence of presence of joint-specific enhanced concentric torque in children. Enhanced concentric torque after eccentric loading at the ankle but not the knee is a positive, robust contributor to dynamic balance, independent of age, sex, height, and muscle strength of the knee and ankle, in children. It is plausible that eccentric-biased exercise training may improve dynamic balance in children warranting future investigations.

Author(s) Disclosures: The authors listed have no conflicts to disclose.