RESUMO
The quick-release technique to estimate musculotendinous (MT) stiffness has been extensively used over the last years, in both animals and humans, to gain insights in the adaptive process of the series elastic component (SEC). Recently, MT stiffness quantification, i.e., SEC behavior, has been revisited for subjects not able to fully activate their muscles (effects of long-term spaceflight or non-mature muscles). Such a phenomenon can also be encountered in stunted children. So, the aim of the present study was to analyze the effect of stunting on MT stiffness taking into account possible defect in muscle activation. For this study, 20 eutrophic children (EU) with an average age of 9years±4months were compared to 11age matched stunted children (S) evaluated by the height-to-age index. The MT stiffness index was obtained with regard to stiffness-torque and stiffness-soleus EMG relationships. The children of the S group presented a significantly lower Maximal Voluntary Contraction (MVC) in plantar flexion in comparison with children of the EU group (-37.8%). The significantly lower MT stiffness index for S children (-42.6%) was evidenced only when quantified with regard to the stiffness-soleus EMG relationship (66.5±42.8 vs. 38.2±19.9 Nmrad(-1)%(-1)). Possible delay in fiber type differentiation or tendinous structure maturation can account for the lower MT stiffness index in S children. In conclusion, stunting during early childhood delays the differentiation and maturation processes of musculotendinous structures as shown by the lower MT stiffness quantified with regards to muscle activity, also altered for stunted prepubertal children.
Assuntos
Eletromiografia/métodos , Transtornos do Crescimento/fisiopatologia , Desnutrição/fisiopatologia , Contração Muscular , Músculo Esquelético/fisiopatologia , Resistência Física , Tendões/fisiopatologia , Criança , Módulo de Elasticidade , Feminino , Transtornos do Crescimento/etiologia , Humanos , Masculino , Desnutrição/complicações , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
The influence of overweight, as a precursor to obesity, was analyzed on the elastic properties of the triceps surae. Based on body mass index (BMI), children (9 years ± 4 mo) were classified as control (CON; n = 23; BMI -1SD>Z score<1SD) or overweight (OW; n = 21, BMI 1SD>Z score<3SD) with regard to reference data from the World Health Organization. Musculotendinous (MT) stiffness of the series elastic component (SEC) was determined using quick-release tests to obtain 1) the MT stiffness index from the slope of either linear stiffness-torque (SI(MT-Torque)) or stiffness-EMG (SI(MT-EMG)) relationships and 2) passive stiffness from the intercept point with the ordinate. Finally, the SEC active (α(0)) and passive fractions (C(passive)) were separated as described by Morgan (Am J Physiol, 1977), using alpha-torque (α(0-Torque,) C(passive-Torque)) or alpha-EMG (α(0-EMG,) C(passive-EMG)) relationships. No significant differences in SI(MT-Torque) or α(0-Torque) were observed between OW and CON. SI(MT-EMG) or α(0-EMG) values were significantly different between OW and CON, which indicate an increase in MT stiffness. In all cases, passive stiffness (K(p), C(passive-torque), C(passive-EMG)) was significantly greater in OW but independent of the activation capacities. These results indicate that a weight-related additional loading of the MT structures in OW children caused the MT system to response accordingly to the functional demand, i.e., higher stiffness of the MT structures due to a concomitant increase in the stiffness of the SEC passive and active fraction. This study also reveals that possible differences in the activation capacities influence the determination of MT stiffness of the SEC active fraction.
Assuntos
Articulação do Tornozelo/fisiologia , Elasticidade/fisiologia , Contração Muscular/fisiologia , Músculo Esquelético/fisiologia , Sobrepeso/fisiopatologia , Antropometria/métodos , Índice de Massa Corporal , Criança , Feminino , Humanos , Masculino , Fenômenos Fisiológicos Musculoesqueléticos , TorqueRESUMO
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 ± 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 (SI(MT)) 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 SI(MT) and EMD values were observed, while K (p) and motor performance in balance were significantly lower. Higher SI(MT) 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.