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1.
Int J Exerc Sci ; 10(4): 580-591, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28674602

RESUMO

The purpose of the present study was to examine the effects of 2 different work-to-rest ratios, but the same mean load, cycle time, and total duration of the exercise bout, on maximal voluntary isometric contraction torque and neuromuscular responses to fatiguing, intermittent, submaximal, isometric, forearm flexion muscle actions. Ten men performed 2 fatiguing protocols with different work-to-rest ratios (4 s contraction, 4 s rest vs. 4 s contraction, alternating 6 and 2 s rest) that consisted of 50 intermittent, submaximal (65% of maximal voluntary isometric contraction), isometric, forearm flexion muscle actions. Electromyographic and mechanomyographic signals from the biceps brachii were recorded before, during, immediately and 5 min after performing the fatiguing protocols. In addition, maximal voluntary isometric contraction torque was assessed before, immediately and 5 min after. Both protocols resulted in decreases in maximal voluntary isometric contraction torque, electromyographic mean power frequency, and mechanomyographic mean power frequency, but no changes in electromyographic amplitude or mechanomyographic amplitude. The results of the present study indicated that differences in work-to-rest ratio did not affect maximal voluntary isometric contraction torque or the associated neuromuscular parameters as a result of fatiguing, intermittent, isometric muscle actions when mean load, cycle time, and total duration of exercise were equivalent.

2.
Physiol Meas ; 37(11): 1993-2002, 2016 11.
Artigo em Inglês | MEDLINE | ID: mdl-27754975

RESUMO

The purposes of the present study were to apply a unique method for the identification of the time course of changes in neuromuscular responses and to infer the motor unit activation strategies used to maintain force during a fatiguing, intermittent isometric workbout. Eleven men performed 50, 6 s intermittent isometric muscle actions of the leg extensors, each separated by 2 s of rest at 60% maximal voluntary isometric contraction (MVIC). Electromyographic (EMG) and mechanomyographic (MMG) amplitude (root mean square; RMS) and frequency (mean power frequency; MPF) were obtained from the vastus lateralis (VL) every 5 of the 50 repetitions and normalized as a percent of the initial repetition. Polynomial regression analyses were used to determine the model of best fit for the normalized EMG RMS, EMG MPF, MMG RMS, and MMG MPF versus repetition relationships and one-way repeated measures ANOVAs with post-hoc Student Newman-Keuls were used to identify when these neuromuscular parameters changed from the initial repetition. The findings of the present study indicated two unique phases of neuromuscular responses (repetitions 1-20 and 20-50) during the fatiguing workbout. The time course of changes in these four neuromuscular responses suggested that the after-hyperpolarization theory could not explain the maintenance of force production, but Muscle Wisdom and the Onion Skin Scheme could. The findings of the current study suggested that the time course of changes in neuromuscular responses can provide insight in to the motor unit activation strategies used to maintain force production and allow for a greater understanding of the fatiguing process by identifying the time-points at which these neuromuscular parameters changed.


Assuntos
Fadiga/fisiopatologia , Contração Isométrica , Músculos/fisiologia , Neurônios/citologia , Eletromiografia , Humanos , Masculino , Análise de Regressão , Processamento de Sinais Assistido por Computador , Adulto Jovem
3.
J Strength Cond Res ; 30(10): 2697-2702, 2016 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-27658233

RESUMO

Smith, CM, Housh, TJ, Herda, TJ, Zuniga, JM, Camic, CL, Bergstrom, HC, Smith, DB, Weir, JP, Hill, EC, Cochrane, KC, Jenkins, NDM, Schmidt, RJ, and Johnson, GO. Time course of changes in neuromuscular parameters during sustained isometric muscle actions. J Strength Cond Res 30(10): 2697-2702, 2016-The objective of the present study was to identify the time course of changes in electromyographic (EMG) and mechanomyographic (MMG) time and frequency domain parameters during a sustained isometric muscle action of the leg extensors at 50% maximal voluntary isometric contraction. The EMG and MMG signals were measured from the vastus lateralis of 11 subjects to identify when motor unit activation strategies changed throughout the sustained isometric muscle action. The EMG amplitude (muscle activation) had a positive linear relationship (p = 0.018, r = 0.77) that began to increase at the initiation of the muscle action and continued until task failure. Electromyographic frequency (motor unit action potential conduction velocity) and MMG frequency (global motor unit firing rate) had negative quadratic relationships (p = 0.002, R = 0.99; p = 0.015, R = 0.94) that began to decrease at 30% of the time to exhaustion. The MMG amplitude (motor unit activation) had a cubic relationship (p = 0.001, R = 0.94) that increased from 10 to 30% of the time to exhaustion, then decreased from 40 to 70% of the time to exhaustion, and then markedly increased from 70% to task failure. The time course of changes in the neuromuscular parameters suggested that motor unit activation strategies changed at approximately 30 and 70% of the time to exhaustion during the sustained isometric muscle action. These findings indicate that the time course of changes in neuromuscular responses provide insight into the strategies used to delay the effects of fatigue and are valuable tools for quantifying changes in the fatiguing process during training programs or supplementation research.

4.
Exp Gerontol ; 84: 1-11, 2016 11.
Artigo em Inglês | MEDLINE | ID: mdl-27521997

RESUMO

The purpose of this study was to investigate the effects of 8weeks at 6g per day of RAR CLA versus placebo on cognitive function and handgrip performance in older men and women. Sixty-five (43 women, 22 men) participants (mean±SD; age=72.4±5.9yrs; BMI=26.6±4.2kg·m-2) were randomly assigned to a RAR CLA (n=30: 10 men, 20 women) or placebo (PLA; high oleic sunflower oil; n=35: 12 men, 23 women) group in double-blind fashion and consumed 6g·d-1 of their allocated supplement for 8weeks. Before (Visit 1) and after supplementation (Visit 2), subjects completed the Serial Sevens Subtraction Test (S7), Trail Making Test Part A (TMA) and Part B (TMB), and Rey's Auditory Verbal Learning Test (RAVLT) to measure cognitive function. The RAVLT included 5, 15-item auditory word recalls (R1-5), an interference word recall (RB), a 6th word recall (R6), and a 15-item visual word recognition trial (RR). For handgrip performance, subjects completed maximal voluntary isometric handgrip strength (MVIC) testing before (MVICPRE) and after (MVICPOST) a handgrip fatigue test at 50% MVICPRE. Hand joint discomfort was measured during MVICPRE, MVICPOST, and the handgrip fatigue test. There were no treatment differences (p>0.05) for handgrip strength, handgrip fatigue, or cognitive function as measured by the Trail Making Test and Serial Seven's Subtraction Test in men or women. However, RAR CLA supplementation improved cognitive function as indicated by the RAVLT R5 in men. A qualitative examination of the mean change scores suggested that, compared to PLA, RAR CLA supplementation was associated with a small improvement in joint discomfort in both men and women. Longer-term studies are needed to more fully understand the potential impact of RAR CLA on cognitive function and hand joint discomfort in older adults, particularly in those with lower cognitive function.


Assuntos
Envelhecimento , Cognição/efeitos dos fármacos , Força da Mão/fisiologia , Ácidos Linoleicos Conjugados/administração & dosagem , Idoso , Método Duplo-Cego , Fadiga , Feminino , Articulação da Mão/fisiopatologia , Humanos , Masculino , Óleos Vegetais/administração & dosagem , Estudos Prospectivos , Fatores Sexuais , Óleo de Girassol , Estados Unidos
5.
J Strength Cond Res ; 30(8): 2174-85, 2016 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26848545

RESUMO

Jenkins, NDM, Housh, TJ, Buckner, SL, Bergstrom, HC, Cochrane, KC, Hill, EC, Smith, CM, Schmidt, RJ, Johnson, GO, and Cramer, JT. Neuromuscular adaptations after 2 and 4 weeks of 80% versus 30% 1 repetition maximum resistance training to failure. J Strength Cond Res 30(8): 2174-2185, 2016-The purpose of this study was to investigate the hypertrophic, strength, and neuromuscular adaptations to 2 and 4 weeks of resistance training at 80 vs. 30% 1 repetition maximum (1RM) in untrained men. Fifteen untrained men (mean ± SD; age = 21.7 ± 2.4 years; weight = 84.7 ± 23.5 kg) were randomly assigned to either a high-load (n = 7) or low-load (n = 8) resistance training group and completed forearm flexion resistance training to failure 3 times per week for 4 weeks. Forearm flexor muscle thickness (MT) and echo intensity, maximal voluntary isometric (MVIC) and 1RM strength, and the electromyographic, mechanomyographic (MMG), and percent voluntary activation (%VA) responses at 10-100% of MVIC were determined at baseline, 2, and 4 weeks of training. The MT increased from baseline (2.9 ± 0.1 cm) to week 2 (3.0 ± 0.1 cm) and to week 4 (3.1 ± 0.1 cm) for the 80 and 30% 1RM groups. MVIC increased from week 2 (121.5 ± 19.1 Nm) to week 4 (138.6 ± 22.1 Nm) and 1RM increased from baseline (16.7 ± 1.6 kg) to weeks 2 and 4 (19.2 ± 1.9 and 20.5 ± 1.8 kg) in the 80% 1RM group only. The MMG amplitude at 80 and 90% MVIC decreased from baseline to week 4, and %VA increased at 20 and 30% MVIC for both groups. Resistance training to failure at 80 vs. 30% 1RM elicited similar muscle hypertrophy, but only 80% 1RM increased muscle strength. However, these disparate strength adaptations were difficult to explain with neuromuscular adaptations because they were subtle and similar for the 80 and 30% 1RM groups.


Assuntos
Adaptação Fisiológica , Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Treinamento de Força/métodos , Adulto , Eletromiografia , Humanos , Masculino , Músculo Esquelético/anatomia & histologia , Adulto Jovem
6.
Eur J Appl Physiol ; 116(3): 659-61, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-26705244

RESUMO

In this response, we addressed the specific issues raised by Vigotsky et al. and clarified (1) our methods and adherence to electromyographic signal reporting standards, (2) our interpretation of EMG amplitude, and (3) our interpretation of EMG mean power frequency.


Assuntos
Exercício Físico/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Treinamento de Força , Feminino , Humanos , Masculino
7.
J Strength Cond Res ; 30(6): 1743-51, 2016 06.
Artigo em Inglês | MEDLINE | ID: mdl-26566165

RESUMO

The purposes of this study were to examine the effects of the velocity of repeated eccentric muscle actions on the torque and neuromuscular responses during maximal isometric and eccentric muscle actions. Twelve resistance-trained men performed 30 repeated, maximal, eccentric, isokinetic muscle actions at randomly ordered velocities of 60, 120, or 180°·s on separate days. Maximal voluntary isometric contractions (MVICs) were performed before (pretest) and after (posttest) the repeated eccentric muscle actions on each day. Eccentric isokinetic peak torque (EIPT) values were the averages of the first 3 and last 3 repetitions of the 30 repeated eccentric muscle actions. During the EIPT and MVIC muscle actions, electromyographic (EMG) and mechanomyographic (MMG) amplitude (EMG AMP and MMG AMP) and mean power frequency (EMG MPF and MMG MPF) values were assessed. These results indicated that the repeated eccentric muscle actions had no effects on EIPT, or the EMG AMP, EMG MPF, or MMG MPF values assessed during the EIPT muscle actions, but decreased MMG AMP. The repeated eccentric muscle actions, however, decreased MVIC torque, and also the EMG AMP and MMG MPF values assessed during the MVIC muscle actions, but increased MMG AMP. The results indicated that the velocity of the repeated eccentric muscle actions affected the MVIC torque responses, but not EIPT or any of the neuromuscular parameters. Furthermore, there are differences in the torque and neuromuscular responses for isometric vs. eccentric muscle actions after repeated eccentric muscle actions.


Assuntos
Eletromiografia/métodos , Contração Isométrica/fisiologia , Músculo Esquelético/fisiologia , Torque , Acelerometria , Adulto , Humanos , Masculino , Miografia/métodos , Processamento de Sinais Assistido por Computador
8.
Appl Physiol Nutr Metab ; 40(11): 1178-85, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26481288

RESUMO

Ten subjects performed four 8-min rides (65%-80% peak oxygen consumption) to determine the physical working capacity at the OMNI rating of perceived exertion (RPE) threshold (PWCOMNI). Polynomial regression analyses were used to examine the patterns of responses for surface electromyographic (EMG) amplitude (EMG AMP), EMG mean power frequency (EMG MPF), mechanomyographic (MMG) AMP, and MMG MPF of the vastus lateralis as well as oxygen consumption rate, respiratory exchange ratio (RER), and power output (PO) were examined during a 1-h ride on a cycle ergometer at a constant RPE that corresponded to the PWCOMNI. EMG AMP and MMG MPF tracked the decreases in oxygen consumption rate, RER, and PO, while EMG MPF and MMG AMP tracked RPE. The decreases in EMG AMP and MMG MPF were likely attributable to decreases in motor unit (MU) recruitment and firing rate, while the lack of change in MMG AMP may have resulted from a balance between MU de-recruitment as PO decreased, and an increase in the ability of activated fibers to oscillate. The current findings suggested that during submaximal cycle ergometry at a constant RPE, MU de-recruitment and mechanical changes within the muscle may influence the perception of effort via feedback from group III and IV afferents.


Assuntos
Ciclismo , Eletromiografia , Metabolismo Energético , Teste de Esforço , Exercício Físico , Mecanotransdução Celular , Contração Muscular , Músculo Esquelético/fisiologia , Percepção , Esforço Físico , Potenciais de Ação , Adulto , Vias Aferentes/fisiologia , Retroalimentação Sensorial , Feminino , Humanos , Masculino , Músculo Esquelético/inervação , Músculo Esquelético/metabolismo , Consumo de Oxigênio , Recrutamento Neurofisiológico , Taxa Respiratória , Fatores de Tempo , Adulto Jovem
9.
Eur J Appl Physiol ; 115(11): 2335-47, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26159316

RESUMO

PURPOSE: The purpose of this study was to investigate electromyographic amplitude (EMG AMP), EMG mean power frequency (MPF), exercise volume (VOL), total work and muscle activation (iEMG), and time under concentric load (TUCL) during, and muscle cross-sectional area (mCSA) before and after 3 sets to failure at 80 vs. 30 % 1RM resistance exercise. METHODS: Nine men (mean ± SD, age 21.0 ± 2.4 years, resistance training week(-1) 6.0 ± 3.7 h) and 9 women (age 22.8 ± 3.8 years, resistance training week(-1) 3.4 ± 3.5 h) completed 1RM testing, followed by 2 experimental sessions during which they completed 3 sets to failure of leg extension exercise at 80 or 30 % 1RM. EMG signals were collected to quantify EMG AMP and MPF during the initial, middle, and last repetition of each set. Ultrasound was used to assess mCSA pre- and post-exercise, and VOL, total work, iEMG, and TUCL were calculated. RESULTS: EMG AMP remained greater at 80 % than 30 % 1RM across all reps and sets, despite increasing 74 and 147 % across reps at 80 and 30 % 1RM, respectively. EMG MPF decreased across reps at 80 and 30 % 1RM, but decreased more and was lower for the last reps at 30 than 80 % 1RM (71.6 vs. 78.1 % MVIC). mCSA increased more from pre- to post-exercise for 30 % (20.2-24.1 cm(2)) than 80 % 1RM (20.3-22.8 cm(2)). VOL, total work, iEMG and TUCL were greater for 30 % than 80 % 1RM. CONCLUSION: Muscle activation was greater at 80 % 1RM. However, differences in volume, metabolic byproduct accumulation, and muscle swelling may help explain the unexpected adaptations in hypertrophy vs. strength observed in previous studies.


Assuntos
Exercício Físico/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Treinamento de Força , Adolescente , Adulto , Eletromiografia , Feminino , Humanos , Masculino , Força Muscular/fisiologia , Adulto Jovem
10.
Eur J Appl Physiol ; 115(10): 2231-41, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26108674

RESUMO

PURPOSE: This study examined: (1) the sustainability of the critical heart rate (CHR) minus 5 b min(-1) (CHR - 5) and CHR plus 5 b min(-1) (CHR + 5); (2) the ratings of perceived exertion (RPE), velocity, [Formula: see text], minute ventilation ([Formula: see text]), breathing frequency (f b ), and electromyographic amplitude (EMG AMP) and EMG mean power frequency (MPF) responses during treadmill running at CHR - 5 and CHR + 5 to determine what factors underlie the perception of effort when heart rate (HR) is held constant; and (3) the relationships among RPE, [Formula: see text], and HR, to determine which variable(s) reflect exhaustion during exercise performed at a constant HR. METHODS: The CHR was determined in eight runners (mean ± SD; age = 24 ± 3 years) from a series of four exhaustive, constant velocity runs. The RPE, velocity, [Formula: see text], [Formula: see text], f b , EMG AMP, and EMG MPF responses were recorded during runs at the CHR - 5 and CHR + 5. RESULTS: At CHR - 5, RPE, f b, and EMG MPF increased, while velocity, [Formula: see text], [Formula: see text], and EMG AMP decreased. At CHR + 5, RPE and f b increased, velocity, [Formula: see text], [Formula: see text], and EMG AMP decreased, and EMG MPF remained constant. CONCLUSIONS: The close association between f b and RPE throughout the run at CHR - 5 and during the last 50 % of the run at CHR + 5 indicated that muscle afferents may have provided feedback from metabolic and mechanical stimuli that contributed to the perceptual responses. In addition, only RPE consistently indicated exhaustion and the current findings supported its use to monitor exercise performed at a constant HR.


Assuntos
Frequência Cardíaca , Esforço Físico , Adolescente , Adulto , Pressão Sanguínea , Humanos , Masculino , Corrida/fisiologia
11.
J Electromyogr Kinesiol ; 25(4): 565-70, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26014918

RESUMO

The purposes of the present study were to examine the effects of electrode placements over, proximal, and distal to the innervation zone (IZ) on electromyographic (EMG) amplitude (RMS) and frequency (MPF) responses during: (1) a maximal voluntary isometric contraction (MVIC), and; (2) a sustained, submaximal isometric muscle action. A linear array was used to record EMG signals from the vastus lateralis over the IZ, 30mm proximal, and 30mm distal to the IZ during an MVIC and a sustained isometric muscle action of the leg extensors at 50% MVIC. During the MVIC, lower EMG RMS (p>0.05) and greater EMG MPF (p<0.05) values were recorded over the IZ compared to away from the IZ, however, no differences in slope coefficients for the EMG RMS and MPF versus time relationships over, proximal, and distal to the IZ occurred. Thus, the results of the present study indicated that during an MVIC, EMG RMS and MPF values recorded over the IZ are not comparable to those away from the IZ. However, the rates of fatigue-induced changes in EMG RMS and MPF during sustained, submaximal isometric muscle actions of the leg extensors were the same regardless of the electrode placement locations relative to the IZ.


Assuntos
Eletromiografia/métodos , Contração Isométrica/fisiologia , Músculo Quadríceps/inervação , Músculo Quadríceps/fisiologia , Eletrodos , Eletromiografia/instrumentação , Feminino , Humanos , Masculino , Músculo Esquelético/inervação , Músculo Esquelético/fisiologia , Fatores de Tempo , Adulto Jovem
12.
J Strength Cond Res ; 29(6): 1473-9, 2015 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-25785708

RESUMO

The purpose of this study was to determine the relative contributions of isokinetic forearm flexion (FLX) and extension (EXT) peak torque (PT) at 180°·s, height (HT), percent body fat (%BF), and fat-free mass (FFM) to the prediction of estimated propulsive force (EPF) and which of these variables should be a focus of training in young male swimmers. Thirty young male swimmers (mean age ± SD = 12.4 ± 2.7 years) volunteered for this study. The subjects were members of local swimming clubs who competed in the front crawl. The swimmers were measured for FLX and EXT PT at 180°·s, HT, body mass (BM), arm muscle area (AMA), arm circumference, triceps skinfold, %BF, and FFM. Arm muscle area was used to calculate EPF. Zero-order correlations and stepwise multiple regression analyses were used to examine the relationships among variables and the relative contributions of FLX, EXT, HT, %BF, and FFM to the prediction of EPF. Forearm flexion PT at 180°·s, EXT, BM, HT, FFM, AMA, and EPF were significantly intercorrelated (r = 0.83-1.00). In addition, 4 variables contributed significantly to the prediction of EPF (standardized regression coefficients = FFM [1.00], FLX [0.92], EXT [-0.62], and HT [-0.35]). Percent body fat did not contribute to any of the stepwise models. These findings suggested that age-related increases in HT and FFM, as well as training for increases in FLX and EXT strength may improve propulsive force and swimming performance in young male swimmers.


Assuntos
Pesos e Medidas Corporais , Força Muscular , Músculo Esquelético/fisiologia , Natação/fisiologia , Adiposidade , Adolescente , Estatura , Peso Corporal , Criança , Antebraço/fisiologia , Humanos , Masculino , Pregas Cutâneas , Torque
13.
Ultrasound Med Biol ; 41(6): 1584-91, 2015 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-25746907

RESUMO

This study compared test-retest reliability and sensitivity to change for muscle size and echo intensity (EI) measurements from single transverse (EIST) versus panoramic (EIP) ultrasound (US) images of the biceps brachii. Forearm flexor muscle thickness and EIST and biceps brachii muscle cross-sectional area and EIP were quantified from single transverse and panoramic US images in 14 men (age = 21.8 ± 2.5 y [mean ± standard deviation]) on two separate days. The intra-class correlation coefficients, coefficients of variation, and minimum differences for muscle thickness, EIST, muscle cross-sectional area and EIP ranged from 0.78 to 0.99, from 2.26% to 3.29%, and from 6.26% to 9.12%, respectively. These findings suggested that single transverse imaging and panoramic US imaging are comparable, reliable techniques for quantifying muscle size and EI of the biceps brachii. Single transverse images may be simpler to obtain; thus, future studies may choose to quantify muscle size and EI from a single transverse US image in the biceps brachii.


Assuntos
Antebraço/anatomia & histologia , Antebraço/diagnóstico por imagem , Músculo Esquelético/anatomia & histologia , Músculo Esquelético/diagnóstico por imagem , Adulto , Humanos , Masculino , Valores de Referência , Reprodutibilidade dos Testes , Ultrassonografia , Adulto Jovem
14.
J Strength Cond Res ; 29(8): 2237-48, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-25647653

RESUMO

The mathematical model used to estimate critical power has been applied to heart rate (HR) measurements during cycle ergometry to derive a fatigue threshold called the critical heart rate (CHR). This study had 2 purposes: (a) determine if the CHR model for cycle ergometry could be applied to treadmill running and (b) examine the times to exhaustion (Tlim) and the VO2 responses during constant HR runs at the CHR. Thirteen runners (mean ± SD; age = 23 ± 3 years) performed an incremental treadmill test to exhaustion. On separate days, 4 constant velocity runs to exhaustion were performed. The total number of heart beats (HBlim) for each velocity was calculated as the product of the average 5-second HR and Tlim. The CHR was the slope coefficient of the HBlim vs. Tlim relationship. The Tlim and VO2 responses were recorded during a constant HR run at the CHR. Polynomial regression analyses were used to examine the patterns of responses for VO2 and velocity. The HBlim vs. Tlim relationship (r = 0.995-1.000) was described by the linear equation: HBlim = a + CHR (Tlim). The CHR (176 ± 7 b·min, 91 ± 3% HRpeak) was maintained for 47.84 ± 11.04 minutes. There was no change in HR but quadratic decreases in velocity and VO2. These findings indicated that the CHR model for cycle ergometry was applicable to treadmill running and represented a sustainable (30-60 minutes) intensity but cannot be used to demarcate exercise intensity domains.


Assuntos
Ergometria , Frequência Cardíaca , Modelos Teóricos , Resistência Física , Corrida/fisiologia , Adulto , Teste de Esforço , Fadiga/fisiopatologia , Feminino , Humanos , Masculino , Consumo de Oxigênio , Esforço Físico , Adulto Jovem
15.
Muscle Nerve ; 52(1): 120-30, 2015 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-25363299

RESUMO

INTRODUCTION: We compared absolute and normalized values for peak torque (PT), mean power (MP), rate of velocity development, and electromyography (EMG) amplitude during maximal isometric and concentric isokinetic leg extension muscle actions, as well as the %decrease in PT and %increase in MP from 1.05 to 3.14 rad·s(-1) in younger versus older men. METHODS: Measurements were performed twice for reliability. Isokinetic measurements were normalized to the isometric muscle actions. RESULTS: Absolute isometric PT, isokinetic PT and MP, and EMG amplitudes at 1.05 and 3.14 rad·s(-1) were greater in the younger men, although normalizing to isometric PT eliminated the age differences. The older men exhibited greater %decrease in PT (37.2% vs. 31.3%) and lower %increase in MP (87.6% vs. 126.4%) regardless of normalization. CONCLUSIONS: Normalization eliminated absolute differences in isokinetic strength and power, but the relative differences from slow to fast velocities may reflect dynapenia characterized by age-related decreases in fast-twitch fiber function.


Assuntos
Contração Muscular/fisiologia , Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Sarcopenia/diagnóstico , Sarcopenia/fisiopatologia , Adolescente , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Análise de Variância , Eletromiografia , Humanos , Perna (Membro)/inervação , Masculino , Dinamômetro de Força Muscular , Torque , Adulto Jovem
16.
J Strength Cond Res ; 29(2): 408-15, 2015 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-24513619

RESUMO

The purposes of this study were to: (a) examine the age-related patterns of differences in height (HT), body mass (BM), percent body fat (% fat), body mass index (BMI), and skinfolds (SF) in 11- to 18-year-old wrestlers; (b) determine the coherence of direct (% fat) and indirect (BMI and SFs) indicators of adiposity in the wrestlers; and (c) compare the age-related patterns and mean values for HT, BM, BMI, subscapular, and triceps SF for the wrestlers to those of national samples of boys from the National Health and Nutrition Examination Survey (NHANES) database. One hundred thirty wrestlers were divided into 8 independent yearly age groups (AG): AG11-AG18 years. Height, BM, BMI, subscapular SF, triceps SF, medial calf SF, thigh SF, sum of SFs, and % fat were assessed. There were no differences between the wrestlers and NHANES samples for age-related patterns of BMI (0.61 and 0.63 kg·m·y), subscapular SF (0.47 and 0.37 mm·y), or triceps SF (-0.31 and -0.39 mm·y). Furthermore, the wrestlers displayed no differences in % fat between age groups. The results indicated that: (a) dissociations existed between the direct and indirect indicators of adiposity; (b) the wrestlers were similar in height but had smaller upper-body SFs when compared with NHANES samples; and (c) participation in wrestling (1-8 years) had no adverse effects on the normal age-related growth patterns for HT, but favorable effects on measures of adiposity.


Assuntos
Adiposidade , Luta Romana/fisiologia , Adolescente , Fatores Etários , Estatura , Índice de Massa Corporal , Criança , Estudos Transversais , Humanos , Masculino , Inquéritos Nutricionais , Pregas Cutâneas
17.
Exp Gerontol ; 58: 47-50, 2014 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-25019471

RESUMO

PURPOSE: To quantify the reliability of isometric leg extension torque (LEMVC), rate of torque development (LERTD), isometric handgrip force (HGMVC) and RFD (HGRFD), isokinetic leg extension torque and power at 1.05rad·s(-1) and 3.14rad·s(-1); and explore relationships among strength, power, and balance in older men. METHODS: Sixteen older men completed 3 isometric handgrips, 3 isometric leg extensions, and 3 isokinetic leg extensions at 1.05rad·s(-1) and 3.14rad·s(-1) during two visits. Intraclass correlation coefficients (ICCs), ICC confidence intervals (95% CI), coefficients of variation (CVs), and Pearson correlation coefficients were calculated. RESULTS: LERTD demonstrated no reliability. The CVs for LERTD and HGRFD were ≤23.26%. HGMVC wasn't related to leg extension torque or power, or balance (r=0.14-0.47; p>0.05). However, moderate to strong relationships were found among isokinetic leg extension torque at 1.05rad·s(-1) and 3.14rad·s(-1), leg extension mean power at 1.05rad·s(-1), and functional reach (r=0.51-0.95; p≤0.05). CONCLUSIONS: LERTD and HGRFD weren't reliable and shouldn't be used as outcome variables in older men. Handgrip strength may not be an appropriate surrogate for lower body strength, power, or balance. Instead, perhaps handgrip strength should only be used to describe upper body strength or functionality, which may compliment isokinetic assessments of lower body strength, which were reliable and related to balance.


Assuntos
Envelhecimento , Avaliação Geriátrica/métodos , Força da Mão , Contração Isométrica , Músculo Esquelético/fisiologia , Equilíbrio Postural , Fatores Etários , Idoso , Humanos , Extremidade Inferior , Masculino , Dinamômetro de Força Muscular , Valor Preditivo dos Testes , Reprodutibilidade dos Testes , Fatores Sexuais , Torque , Extremidade Superior
18.
Lipids ; 49(9): 871-80, 2014 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-25034667

RESUMO

This study examined the effects of 6 weeks of conjugated linoleic acid (CLA) supplementation and moderate aerobic exercise on peak oxygen uptake (VO2 peak), the gas exchange threshold (GET), the respiratory compensation point (RCP), and serum concentrations of cholesterol, triacylglycerol, and glucose in humans. Thirty-four untrained to moderately trained men (mean ± SD; age = 21.5 ± 2.8 years; mass = 77.2 ± 9.5 kg) completed this double-blind, placebo controlled study and were randomly assigned to either a CLA (Clarinol A-80; n = 18) or placebo (PLA; sunflower oil; n = 16) group. Prior to and following 6 weeks of aerobic training (50% VO2 peak for 30 min, twice per week) and supplementation (5.63 g of total CLA isomers [of which 2.67 g was c9, t11 and 2.67 g was t10, c12] or 7.35 g high oleic sunflower oil per day), each participant completed an incremental cycle ergometer test to exhaustion to determine their [Formula: see text] peak, GET, and RCP and fasted blood draws were performed to measure serum concentrations of cholesterol, triacylglycerol, and glucose. Serum triacylglycerol concentrations were lower (p < 0.05) in the CLA than the PLA group. For VO2 peak and glucose, there were group × time interactions (p < 0.05), however, post hoc statistical tests did not reveal any differences (p > 0.05) between the CLA and PLA groups. GET and RCP increased (p < 0.05) from pre- to post-training for both the CLA and PLA groups. Overall, these data suggested that CLA and aerobic exercise may have synergistic, blood triacylglycerol lowering effects, although CLA may be ineffective for enhancing aerobic exercise performance in conjunction with a 6-week aerobic exercise training program in college-age men.


Assuntos
Exercício Físico , Fadiga/fisiopatologia , Ácidos Linoleicos Conjugados/farmacologia , Oxigênio/farmacocinética , Triglicerídeos/sangue , Glicemia/metabolismo , Pressão Sanguínea/efeitos dos fármacos , Colesterol/sangue , Suplementos Nutricionais , Método Duplo-Cego , Frequência Cardíaca/efeitos dos fármacos , Humanos , Masculino , Troca Gasosa Pulmonar , Respiração/efeitos dos fármacos , Adulto Jovem
19.
Exp Gerontol ; 57: 18-28, 2014 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-24806786

RESUMO

The purpose of this study was to compare the voluntary and evoked, absolute and normalized leg extension rates of torque development (RTD) and rates of rise in electromyography (RER) during commonly reported time intervals in young and old men. Fourteen young men (21.9±3.2years) and 16 older men (72.3±7.3years) completed three evoked and three voluntary isometric leg extension muscle actions to quantify absolute voluntary (peak, 30, 50, 100, and 200ms) and evoked (peak, 30, 50, and 100ms) RTD and RER. All RTD values were normalized (nRTD) to peak torque, while RER values were normalized (nRER) to peak-to-peak M-wave amplitude (MPP). Absolute voluntary RTDs and RERs were 58-122% and 70-76% greater (p≤0.05) for the young men, respectively. However, there were no age-related differences (p>0.05) for voluntary nRTDs, absolute and normalized evoked RTDs, or voluntary nRER. MPP and evoked RER and nRER were greater (p≤0.05) for the young men. In addition, voluntary RTD was more reliable in the young than the older men. Normalizing RTD to peak torque and RER to M-wave amplitude eliminated the age-related differences and suggested that the age-related declines in RTD and RER were a result of reduced muscle strength and M-wave amplitude, respectively. Therefore, our findings questioned the value of RTD and RER measurements in the various time intervals for explaining sarcopenia and suggested that maximal strength and M-wave amplitude may be sufficient.


Assuntos
Envelhecimento/fisiologia , Eletromiografia , Músculo Esquelético/fisiologia , Idoso , Idoso de 80 Anos ou mais , Voluntários Saudáveis , Humanos , Perna (Membro)/fisiologia , Torque , Adulto Jovem
20.
J Strength Cond Res ; 28(8): 2127-35, 2014 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-24796987

RESUMO

The purpose of this study was to examine the effects of conjugated linoleic acid (CLA) supplementation in conjunction with 6 weeks of aerobic exercise training on the physical working capacity at the fatigue threshold (PWCFT), timed sit-ups, and the standing long jump. Thirty-three untrained to moderately trained men (mean ± SD; age = 21.6 ± 2.8 years) participated in this double-blind, placebo-controlled study and were randomly assigned to either a CLA (Clarinol A-80; n = 17) or placebo (PLA; sunflower oil; n = 16) group. Before and after 6 weeks of aerobic training (50% VO2peak for 30 minutes, twice per week) and supplementation (8 ml CLA or PLA per day), each subject completed an incremental cycle ergometer test to exhaustion to determine the PWCFT, maximal number of sit-ups in 1 minute, and the standing long jump. There were no differences (all p ≥ 0.23) between the CLA and PLA groups for the analysis of covariance-adjusted posttest mean values for PWCFT, sit-ups, or standing long jump. The PWCFT increased from pre- to posttraining in the CLA (p = 0.003) and PLA (p = 0.003) groups. There were no differences (p > 0.05) from pre- to posttraining for sit-ups and standing long jump in either the CLA or PLA groups. There was no effect of CLA on the training-induced increases in PWCFT, nor were there any effects of CLA or aerobic training on the maximum number of sit-ups or standing long jump. Thus, CLA had no ergogenic benefits on this model of aerobic training-induced improvements in neuromuscular fatigue, or on field tests of muscle endurance and power.


Assuntos
Exercício Físico/fisiologia , Fadiga/fisiopatologia , Ácido Linoleico/administração & dosagem , Condicionamento Físico Humano/fisiologia , Resistência Física/fisiologia , Adolescente , Suplementos Nutricionais , Método Duplo-Cego , Teste de Esforço , Humanos , Masculino , Adulto Jovem
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