RESUMO

Early life is critical for the programming of body composition. The literature links perinatal factors with fat mass development and its future effects (e.g., obesity); however, little evidence exists between early life factors and lean body mass (LBM). This study follows up on a cohort of 416 Spanish children at ages six to eight, previously evaluated at birth in the CALINA study. Here, we studied the association between early life factors, LBM, and limb strength. Parental origin/nutritional status, maternal smoking during pregnancy, gestational diabetes/weight gain/age, birth weight (BW), early feeding, and rapid weight gain (RWG) were collected from primary care records. Bioimpedance analysis, dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, and a handgrip/standing long jump test were used to assess fat-free mass index (FFMI), total lean soft tissue mass index (TLSTMI), muscle cross-sectional area index (MCSAI), and limb strength, respectively. In girls, maternal smoking, gestational age, and BW were positively associated with FFM/LSTM. In boys, the parents' BMI, BW, and RWG were positively associated with FFM/LSTM. BW was associated with handgrip strength in both. Maternal BMI in girls and RWG in boys were negatively associated with the standing long jump. Early life programming plays a key role in determining LBM in children.

RESUMO

The present study investigated the associations between physical activity (PA) and physical fitness (PF) with lean body mass (LBM) and evaluated whether PA mediates the association between PF and LBM. 279 children (150 boys) aged 7.5 ± 0.3 years participated in the study. PA was assessed by accelerometry and PF with handgrip and the standing long jump test. Total lean soft tissue mass index (TLSTMI), muscle cross-sectional area index (MCSAI), and fat-free mass index (FFMI) were evaluated using dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, and bioimpedance analysis, respectively.Total (ß = 0.247) and vigorous PA (ß = 0.143) were associated with TLSTMI in girls. In boys, total (ß = 0.337), light (ß = 0.290), vigorous (ß = 0.200), and moderate-vigorous PA (ß = 0.189) were associated with TLSTMI. Total PA was associated with FFMI (ß = 0.299). Handgrip strength does not mediate the relationship between total PA and TLSTMI. Positive associations were found between handgrip strength and TLSTMI, MCSAI, and FFMI in both girls and boys.In children, there is a positive association between total and vigorous PA with TLSTMI. Handgrip strength does not mediate the relationship between total PA and TLSTMI. It was associated with TLSTMI, MCSAI, and FFMI.

Assuntos

RESUMO

BACKGROUND: This study investigated the effects of two 14-week resistance training protocols with different repetition duration (RD) performed to muscle failure (MF) on gains in strength and muscle hypertrophy as well as on normalized electromyographic (EMG) amplitude and force-angle relationships. METHODS: The left and right legs of ten untrained males were assigned to either one of the two protocols (2-s or 6-s RD) incorporating unilateral knee extension exercise. Both protocols were performed with 3-4 sets, 50-60% of the one-repetition maximum (1RM), and 3 min rest. Rectus femoris and vastus lateralis cross-sectional areas (CSA), maximal voluntary isometric contraction (MVIC) at 30o and 90o of knee flexion and 1RM performance were assessed before and after the training period. In addition, normalized EMG amplitude-angle and force-angle relationships were assessed in the 6th and 39th experimental sessions. RESULTS: The 6-s RD protocol induced larger gains in MVIC at 30o of knee angle measurement than the 2-s RD protocol. Increases in MVIC at 90o of knee angle, 1RM, rectus femoris and vastus lateralis CSA were not significant between the 2-s and 6-s RD protocols. Moreover, different normalized EMG amplitude-angle and force-angle values were detected between protocols over most of the angles analyzed. CONCLUSION: Performing longer RD could be a more appropriate strategy to provide greater gains in isometric maximal muscle strength at shortened knee positions. However, similar maximum dynamic strength and muscle hypertrophy gains would be provided by protocols with different RD.

RESUMO

BACKGROUND: Skeletal muscle is one of the main components of lean soft tissue mass (LSTM). Low levels in children affect locomotion, posture, and increase the risk of metabolic syndrome. AIM: (1) To evaluate the association between muscle cross-sectional area (MCSA) of the lower left leg measured by peripheral quantitative computed tomography (pQCT) and total LSTM; namely, total left leg and left lower leg LSTM assessed by dual-energy X-ray absorptiometry (DXA) in a group of children, (2) to examine if MCSA is a predictor of LSTM, (3) to determine the ability of pQCT to identify children with low LSTM. SUBJECTS AND METHODS: Lower left leg MCSA and LSTM were measured using pQCT and DXA, respectively, in 396 children. RESULTS: Statistically significant positive correlations were found between the lower leg MCSA - total LSTM (r² = 0.789), total leg LSTM (r² = 0.79), and lower leg LSTM (r² = 0.791) (p < .01). MCSA explained 64-68% of the variance in LSTM. Receiver operator characteristic (ROC) curves determined the capacity of the lower left leg MCSA to identify low LSTM in girls (AUC 0.95) and boys (AUC 0.87). CONCLUSIONS: Our results showed that lower left leg MCSA, measured using pQCT, could be a tool to predict low LSTM in children.

Assuntos

RESUMO

The aim of the study was to compare the effect of resistance training (RT) frequencies of five times (RT5), thrice- (RT3) or twice- (RT2) weekly in muscle strength and hypertrophy in young men. Were used a within-subjects design in which 20 participants had one leg randomly assigned to RT5 and the other to RT3 or to RT2. 1 RM and muscle cross-sectional area (CSA) were assessed at baseline, after four (W4) and eight (W8) RT weeks. RT5 resulted in greater total training volume (TTV) than RT3 and RT2 (P = .001). 1 RM increased similarly between protocols at W4 (RT5: 55 ± 9 Kg, effect size (ES): 1.18; RT3: 51 ± 11 Kg, ES: 0.80; RT2: 54 ± 7 Kg, ES: 1.13; P < .0001) and W8 (RT5: 62 ± 11 Kg, ES: 1.81; RT3: 57 ± 11 Kg, ES: 1.40; RT2: 60 ± 8 Kg, ES: 1.98; P < .0001) vs. baseline (RT5: 45 ± 9 Kg; RT3: 42 ± 11 Kg; RT2: 46 ± 7 Kg). CSA increased similarly between protocols at W4 (RT5: 24.6 ± 3.9 cm2, ES: 0.54; RT3: 22.0 ± 4.6 cm2, ES: 0.19; RT2: ES: 0.25; 23.8 ± 3.8 cm2; P < .001), and W8 (RT5: 25.3 ± 4.3 cm2; ES: 0.69; RT3: 23.6 ± 4.2 cm2, ES: 0.58; RT2: 25.5 ± 3.7 cm2; ES: 0.70; P < .0001) vs. baseline (RT5: 22.5 ± 3.8 cm2; RT3: 21.2 ± 4.0 cm2; RT2: 22.9 ± 3.8 cm2). Performing RT5, RT3 and RT2 a week result in similar muscle strength increase and hypertrophy, despite higher TTV for RT5.

Assuntos

RESUMO

Summary Objective: The aim was to evaluate the effectiveness of the experimental synergists muscle ablation model to promote muscle hypertrophy, determine the period of greatest hypertrophy and its influence on muscle fiber types and determine differences in bilateral and unilateral removal to reduce the number of animals used in this model. Method: Following the application of the eligibility criteria for the mechanical overload of the plantar muscle in rats, nineteen papers were included in the review. Results: The results reveal a greatest hypertrophy occurring between days 12 and 15, and based on the findings, synergist muscle ablation is an efficient model for achieving rapid hypertrophy and the contralateral limb can be used as there was no difference between unilateral and bilateral surgery, which reduces the number of animals used in this model. Conclusion: This model differs from other overload models (exercise and training) regarding the characteristics involved in the hypertrophy process (acute) and result in a chronic muscle adaptation with selective regulation and modification of fast-twitch fibers in skeletal muscle. This is an efficient and rapid model for compensatory hypertrophy.

Resumo Objetivo: Avaliar a eficácia do modelo experimental de ablação dos sinergistas para promover a hipertrofia muscular, determinar o período de maior hipertrofia, sua influência sobre os tipos de fibras musculares e determinar diferenças na remoção unilateral ou bilateral para reduzir o número de animais utilizados nesse modelo. Método: Após a aplicação dos critérios de elegibilidade para sobrecarga mecânica do músculo plantar em ratos, 19 artigos foram incluídos na revisão. Resultados: Ocorre maior hipertrofia entre os dias 12 e 15, o que torna o modelo eficiente para alcançar a hipertrofia rapidamente. O membro contralateral também pode ser usado, pois não houve diferença entre a cirurgia unilateral e bilateral, o que reduz o número de animais usados no experimento. Conclusão: O modelo difere de outros modelos de sobrecarga (exercício e treinamento) em razão das características envolvidas no processo de sobrecarga imposta (aguda), resultando em uma adaptação crônica muscular com modificação de fibras de contração rápida do músculo esquelético. É um modelo rápido e eficiente para se estudar hipertrofia compensatória.

Assuntos

RESUMO

PURPOSE: The aim of this study was to compare the effects of crescent pyramid (CP) and drop-set (DS) systems with traditional resistance training (TRAD) with equalized total training volume (TTV) on maximum dynamic strength (1-RM), muscle cross-sectional area (CSA), pennation angle (PA), and fascicle length (FL). METHODS: Thirty-two volunteers had their legs randomized in a within-subject design in TRAD (3-5 sets of 6-12 repetitions at 75% 1-RM), CP (3-5 sets of 6-15 repetitions at 65-85% 1-RM), and DS (3-5 sets of ~50-75% 1-RM to muscle failure) protocols. Each leg was trained for 12 weeks. Participants had one leg fixed in the TRAD while the contralateral leg performed either CP or DS to allow for TTV equalization. RESULTS: The CSA increased significantly and similarly for all protocols (TRAD: 7.6%; CP: 7.5%; DS: 7.8%). All protocols showed significant and similar increases in leg press (TRAD = 25.9%; CP = 25.9%; DS = 24.9%) and leg extension 1-RM loads (TRAD = 16.6%; CP = 16.4%; DS = 17.1%). All protocols increased PA (TRAD = 10.6%; CP = 11.0%; DS = 10.3%) and FL (TRAD = 8.9%; CP = 8.9%; DS = 9.1%) similarly. CONCLUSION: CP and DS systems do not promote greater gains in strength, muscle hypertrophy and changes in muscle architecture compared to traditional resistance training.

Assuntos

RESUMO

O presente estudo avaliou a influência de diferentes doses de decanoato de nandrolona (DN) associado ao Treinamento de Força (TF) sobre o fenótipo de fibras e área de secção transversa (AST) do músculo extensor longo dos dedos (EDL) em ratos "Wistar". Os animais foram divididos em sete grupos: controle (GC) e grupos de acordo com a concentração de DN (0,1, 1, 2, 5, 10 e 20 mg/kg) administrada intramuscular 3 vezes/semana. O TF consistiu de saltos em meio líquido (carga 50-70% do peso corporal) 3x/semana, durante cinco semanas. A associação do TF e DN promoveu ação modulatória sobre os tipos de fibras. Houve hipertrofia das fibras de contração rápida (tipo II) em comparação com as fibras de contração lenta (tipo I). Em conclusão, apesar da associação do TF com DN aumentar a AST muscular e alterar o fenótipo das fibras, não houve efeito gradual das doses mais altas.

The aim of the present study was to evaluate the influence of different doses of nandrolone decanoate (ND) associated with Strength Training (ST) on the phenotype of fibers and cross-sectional area (CSA) of the extensor digitorum longus (EDL) in Wistar rats. The animals were divided into seven groups: control (CG) and the groups according to the dose of ND administered (0,1, 1, 2, 5, 10 e 20 mg/kg). The ST consisted of water jumping with loads of 50-70% of their body mass, three times per week during five weeks. The association of ST with ND promoted a modulatory role on the muscle fiber types. There was a hypertrophy of fast twitch fibers (type II) as compared with slow twitch (type I). In conclusion, although the association of ST with ND increased muscle CSA and modified fiber phenotype, there was no additional effect of higher doses.

Assuntos