The bigger, the stronger? Insights from muscle architecture and nervous characteristics in obese adolescent girls.

BACKGROUND: Young obese youth are generally stronger than lean youth. This has been linked to the loading effect of excess body mass, acting as a training stimulus comparable to strength training. Whether this triggers specific adaptations of the muscle architecture (MA) and voluntary activation (VA) that could account for the higher strength of obese subjects remains unknown. METHODS: MA characteristics (that is, pennation angle (PA), fascicle length (FL) and muscle thickness (MT)) and muscle size (that is, anatomical cross-sectional area (ACSA)) of the knee extensor (KE) and plantar flexor (PF) muscles were evaluated in 12 obese and 12 non-obese adolescent girls (12-15 years). Maximal isometric torque and VA of the KE and PF muscles were also assessed. RESULTS: Results revealed higher PA (P<0.05), greater MT (P<0.001), ACSA (P<0.01), segmental lean mass (P<0.001) and VA (P<0.001) for KE and PF muscles in obese girls. Moreover, obese individuals produced a higher absolute torque than their lean counterparts on the KE (224.6±39.5 vs 135.7±32.7 N m, respectively; P<0.001) and PF muscles (73.3±16.5 vs 44.5±6.2 N m; P<0.001). Maximal voluntary contraction (MVC) was correlated to PA for the KE (r=0.46-0.57, P<0.05-0.01) and PF muscles (r=0.45-0.55, P<0.05-0.01). MVC was also correlated with VA (KE: r=0.44, P<0.05; PF: r=0.65, P<0.001) and segmental lean mass (KE: r=0.48, P<0.05; PF: r=0.57, P<0.01). CONCLUSIONS: This study highlighted favorable muscular and nervous adaptations to obesity that account for the higher strength of obese youth. The excess of body mass supported during daily activities could act as a chronic training stimulus responsible for these adaptations.

Children have a reduced maximal voluntary activation level of the adductor pollicis muscle compared to adults.

PURPOSE: The role of nervous factors in the muscle strength difference between children and adults is debated, and the level of physical activity may confound this comparison. The purpose of this study was thus to compare, between children and adults, the maximal voluntary activation level (MVA) of the adductor pollicis (AP) muscle, which is weakly influenced by the level of physical activity. METHODS: Thirteen boys (11.6 ± 0.1 years) and eight men (25.6 ± 1.5 years) were involved in this study. Neuromuscular function assessment included the evaluation of maximal voluntary contraction (MVC) force and of the MVA from peripheral magnetic stimulations of the ulnar nerve. The cross-sectional area of the AP muscle was determined with ultrasonography and used to calculate the specific force. A theoretical value of specific force, extrapolated for a full MVA, was finally computed (specific force@100 % MVA). RESULTS: MVC force (66.8 ± 6.2 vs. 111.0 ± 4.5 N, respectively; P < 0.001) and MVA (85.0 ± 2.7 vs. 94.8 ± 1.4 %, respectively; P < 0.05) were significantly lower in children compared to adults. The specific force was lower in children compared to adults (46.8 ± 3.6 vs. 56.9 ± 2.5 N/cm(2), respectively; P < 0.05), but the specific force@100 % MVA did not differ between groups. CONCLUSION: The results suggest that on an untrained muscle such as the AP muscle, the reduced ability of children to voluntarily activate their muscle could partly account for the difference of muscle strength between children and adults.

Hypocitraturic and hypercalciuric renal tubular acidosis with nephrocalcinosis in a 4-year-old boy.

A 4-year-old boy suffering from hypocitraturic and hypercalciuric renal tubular acidosis with nephrolithiasis and nephrocalcinosis is reported. Renal function tests indicated that the patient had type 1 renal tubular acidosis. Potassium citrate rather than potassium bicarbonate, sodium citrate or bicarbonate is the preferred treatment for stones in RTA-I.

[Clinico-genetic characteristics of hereditary nephritis in different populations]. / Kliniko-geneticheskaia kharakteristika nasledstvennogo nefrita v raznykh populiatsiiakh.

Some data are presented on the clinical features of a course of hereditary nephritis in persons of 13 nationalities residing in the central zone of the RSFSR, in Central Asia and East Slovakia (the Czechoslovak Socialist Republic). At least 2 types of hereditary nephritis transmission (the dominant x-chromosome-linked one was more common than the autosomal-dominant one) not differing in their clinical course were revealed. Basing on a study of the clinical features of a course of disease in 123 autobred and 52 inbred families a more severe course of nephritis was observed in children from the inbred families.