Stunting delays maturation of triceps surae mechanical properties and motor performance in prepubertal children

Malnutrition can lead to possible irreversible consequences in the development of muscle function and some of them are yet poorly characterized. The present study evaluated the mechanical properties of the triceps surae and motor performance in stunted (S) and eutrophic (E) prepubertal children (9 years +/- A 6 months). Height-for-age ratio was used as indicator of stunting due to early malnutrition, according to the World Health Organization. Torque was determined by maximal voluntary contractions (MVC) and musculotendinous (MT) stiffness was achieved through quick-release tests to obtain MT stiffness index (SIMT) and passive stiffness (K (p)) from linear MT stiffness-torque relationships. Percutaneous supramaximal electrically elicited contractions determined twitch torque (Pt) and electromechanical delay (EMD). Motor performance was evaluated by balance test. S group presented significantly lower MVC and a trend of lower Pt values indicating lower capacities to develop force under voluntary or induced conditions. Significantly higher SIMT and EMD values were observed, while K (p) and motor performance in balance were significantly lower. Higher SIMT values have been reported previously in youngest prepubertal children, indicating that immature activation capacities can mask MT stiffness assessment during voluntary contractions, taking into consideration the higher EMD values as a measure of muscle stiffness contribution. Lower K (p) may indicate a delay in the maturation of tendinous tissue in S group, influencing motor performance in balance. The present study shows that malnutrition leads to adaptation of intrinsic MT elastic properties, but depends on the level of the observed structure.