Medicine and science in sports and exercise | 30 Nov 2012
CM Waugh, T Korff, F Fath and AJ Blazevich
Children demonstrate lower force production capacities compared to adults, whichhas often been attributed to ‘neuromuscular immaturity’. However, tendon stiffness, which influences both the electro-mechanical delay (EMD) and rate of force development (RFD) in adults, is lower in children and may influence rapid force production. PURPOSE: The aims of this study were to: 1) document EMD and RFD variation as a function of age, 2) determine the relationships between tendon stiffness and parameters relating to rapid force production in children and adults, and 3) estimate the relative neural and mechanical contributions to age-related changes in force production by examining the effects of tendon stiffness and muscle activation rate (rate of EMG increase; REI) on RFD. METHODS: Achilles tendon stiffness, EMD, RFD and REI were measured duringplantar flexion contractions in 47prepubertal children (5-12 yrs) and 19 adults. Relationships were determined between: 1) stiffness and EMD, 2) stiffness and RFD, and 3) REI and RFD. The relative contributions of age, stiffness and REI on RFD were determined using a multiple regression analysis. Age-related differences in tendon stiffness, EMD, RFD and REI were also examined according to chronological age (5-6, 7-8 and 9-10 years) and compared to adults. RESULTS: Increases in tendon stiffness with age were negatively correlated with EMD (r<-0.83). Stiffness and REI could account for up to 35% and 30% of RFD variability in children, respectively, which increased to 58% when these variables were combined. CONCLUSIONS: Both neural and mechanical factors influence rapid force production in prepubertal children. Children's longer EMD and slower RFD indicate a less effective development and transfer of muscular forces, which may have implications for complex movement performance.
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