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1.
J Mot Behav ; : 1-7, 2021 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-34763617

RESUMO

This study examined the influence of muscle activation and motor unit number estimation (MUNE) on early phase voluntary rate of torque development (RTD) in younger (YM) and older (OM) men. Thirty-two YM (n = 17; Age = 22 yrs) and OM (n = 15; Age = 74 yrs) volunteered to participate in this study. Early phase RTD (first 50 ms of a rapid isometric contraction; RTD50) and normalized surface electromyography (first 50 ms of muscle excitation; nEMG50) were recorded from the right quadricep muscle group. MUNE was examined from the right vastus lateralis. Multiple linear regression analyses revealed that nEMG50 had a significant effect on RTD50 independent of age group (p ≤ 0.001). nEMG50 had a significant effect on RTD50 in the OM group (p = 0.037). MUNE had no effect on RTD50 independent of age. Older adults may depend more on muscle activation at contraction onset of early phase RTD compared to younger adults.

2.
Clin Nutr ; 40(7): 4762-4771, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-34242916

RESUMO

BACKGROUND & AIMS: Individuals with fasting triglycerides (TG) <150 mg/dL can experience a deleterious postprandial TG response ≥220 mg/dL to a high-fat meal (HFM). The purpose of this study was to identify individuals based on fasting TG that would benefit most from additional postprandial screening. METHODS: We conducted a secondary analysis of 7 studies from our laboratories featuring 156 disease-free participants (64 M, 92 F; age 18-70 years; BMI 18.5-30 kg/m2). Participants observed a 10-12 h overnight fast, after which they consumed an HFM (10-13 kcal/kg body mass; 61-64% kcal from fat). Two methods were used to identify lower and upper fasting TG cut points. Method 1 identified the lower limit as the TG concentration at which ≥90% of individuals presented peak postprandial TG (PPTG) <220 mg/dL and the upper limit as the concentration which ≥90% of individuals presented PPTG ≥220 mg/dL. Method 2 utilized receiver operating characteristic (ROC) curves and identified the lower limit as the fasting TG concentration where sensitivity was ≈95% and the upper limit as the concentration at which specificity was ≈95%. RESULTS: In Method 1, 90% of individuals with fasting TG >130 mg/dL (>1.50 mmol/L) exhibited PPTG ≥220 mg/dL (≥2.50 mmol/L), while 100% of individuals with fasting TG <66 mg/dL (0.75 mmol/L) had PPTG that did not exceed 220 mg/dL (2.50 mmol/L). In Method 2, when sensitivity was ≈95%, the corresponding fasting TG concentration was 70 mg/dL (0.79 mmol/L). When specificity was ≈95%, the corresponding fasting TG concentration was 114 mg/dL (1.29 mmol/L). Based on methods 1 and 2, there was a moderate positive association (r = 0.37, p < 0.004) between fasting and PPTG for individuals with fasting TG between 70 and 130 mg/dL (0.79-1.50 mmol/L), in which 24% exhibited PPTG ≥220 mg/dL (≥2.50 mmol/L) while 76% did not. CONCLUSIONS: Postprandial TG testing is likely most useful for individuals with fasting TG concentrations between 70 and 130 mg/dL (0.79-1.50 mmol/L). Outside of this range, postprandial TG responses are largely predictable. Establishing a specific patient group for which postprandial TG testing is most useful may lead to earlier risk detection in these individuals.

3.
Am J Physiol Heart Circ Physiol ; 321(3): H532-H541, 2021 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-34328346

RESUMO

Adverse childhood experiences (ACEs) are psychosocial stressors that occur during sensitive developmental windows and are associated with increased lifetime cardiovascular disease (CVD) risk in a dose-dependent manner. Vascular endothelial dysfunction is a pathophysiological mechanism that promotes hypertension and CVD and may be a mechanism by which ACEs contribute to lifetime CVD risk. We examined whether exposure to ACEs is associated with reduced vascular endothelial function (VEF) in otherwise healthy, young adult women (20.7 ± 3 yr) with (ACE+) versus without (ACE-) ACEs, explored whether differences in circulating sirtuin 1 (SIRT1) or systemic oxidative stress could explain ACEs-related differences in VEF, and examined the ability of a pilot, 8-wk exercise intervention to augment VEF and SIRT1 or reduce oxidized LDL cholesterol (oxLDL) in ACE+ young adult women. Forty-two otherwise healthy young adults completed this study. Prior to the intervention, VEF (P = 0.002) and SIRT1 (P = 0.004) were lower in the ACE+ than ACE- group, but oxLDL concentrations were not different (P = 0.77). There were also significant relationships (P ≤ 0.04) among flow-mediated dilation (FMD), SIRT1, and oxLDL in the ACE+, but not ACE- group. Adjusting for circulating SIRT1 and oxLDL reduced the differences in FMD observed between groups (P = 0.10), but only SIRT1 was a significant adjuster of the means (P < 0.05). Finally, the exercise intervention employed was unable to enhance VEF or SIRT1 in the ACE+ exercise group. Our data suggest that ACEs likely increase susceptibility to hypertension and CVD by causing endothelial dysfunction, perhaps through a SIRT1 pathway-related mechanism.NEW & NOTEWORTHY Our study provides novel evidence that young adult women with moderate-to-severe adverse childhood experience (ACE) exposure present impaired endothelial function and lower circulating sirtuin 1 (SIRT1) concentrations than age-matched controls. However, an 8-wk exercise intervention was unable to augment endothelial function or SIRT1 concentrations in a subset of those with ACEs. Our data suggest that ACEs-related impairments in endothelial function may be secondary to decreased NO bioavailability via SIRT1 and/or oxidative stress-related mechanisms.


Assuntos
Experiências Adversas da Infância , Endotélio Vascular/metabolismo , Estresse Oxidativo , Sirtuína 1/genética , Estresse Psicológico/metabolismo , Adolescente , Adulto , Idoso , Endotélio Vascular/fisiopatologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Sirtuína 1/metabolismo , Estresse Psicológico/etiologia , Estresse Psicológico/fisiopatologia
4.
Clin Nutr ESPEN ; 43: 428-435, 2021 06.
Artigo em Inglês | MEDLINE | ID: mdl-34024551

RESUMO

BACKGROUND & AIMS: Postprandial lipemia (PPL) is predictive of cardiovascular disease risk, but the current method for assessing PPL is a burdensome process. Recently, the validity of an abbreviated fat tolerance test (AFTT) has been demonstrated. As a continuation of this research, the purpose of this study was to determine the reliability of the AFTT and compare it to the reliability of the oral glucose tolerance test (OGTT). METHODS: In this randomized crossover trial, 20 healthy adults (10 male and 10 female) completed 2 AFTTs and 2 OGTTs, each separated by a 1-week washout. For the AFTT, triglycerides (TG) were measured at baseline and 4 h post-consumption of a high-fat meal, during which time participants were able to leave the lab. For the OGTT, we measured blood glucose at baseline and 2 h post-consumption of a 75-g pure glucose solution, and participants remained in the lab. To determine reliability, we calculated within-subject coefficient of variation (WCV) and intraclass correlation coefficient (ICC). RESULTS: The mean 4-h TG WCV for the AFTT was 12.6%, while the mean 2-h glucose WCV for the OGTT was 10.5%. ICC values for 4-h TG and TG change were 0.79 and 0.71, respectively, while ICC values for 2-h glucose and glucose change were 0.66 and 0.56, respectively. CONCLUSIONS: Based on WCV and ICC, the TG response to an AFTT was similarly reliable to the glucose response to an OGTT in our sample of healthy adults, supporting the AFTT's potential as a standard clinical test for determining PPL. However, reliability of the AFTT needs to be further tested in individuals at greater risk for cardiometabolic disease.


Assuntos
Glicemia , Período Pós-Prandial , Adulto , Feminino , Teste de Tolerância a Glucose , Humanos , Masculino , Reprodutibilidade dos Testes , Triglicerídeos
5.
J Int Soc Sports Nutr ; 18(1): 1, 2021 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-33388079

RESUMO

Following critical evaluation of the available literature to date, The International Society of Sports Nutrition (ISSN) position regarding caffeine intake is as follows: 1. Supplementation with caffeine has been shown to acutely enhance various aspects of exercise performance in many but not all studies. Small to moderate benefits of caffeine use include, but are not limited to: muscular endurance, movement velocity and muscular strength, sprinting, jumping, and throwing performance, as well as a wide range of aerobic and anaerobic sport-specific actions. 2. Aerobic endurance appears to be the form of exercise with the most consistent moderate-to-large benefits from caffeine use, although the magnitude of its effects differs between individuals. 3. Caffeine has consistently been shown to improve exercise performance when consumed in doses of 3-6 mg/kg body mass. Minimal effective doses of caffeine currently remain unclear but they may be as low as 2 mg/kg body mass. Very high doses of caffeine (e.g. 9 mg/kg) are associated with a high incidence of side-effects and do not seem to be required to elicit an ergogenic effect. 4. The most commonly used timing of caffeine supplementation is 60 min pre-exercise. Optimal timing of caffeine ingestion likely depends on the source of caffeine. For example, as compared to caffeine capsules, caffeine chewing gums may require a shorter waiting time from consumption to the start of the exercise session. 5. Caffeine appears to improve physical performance in both trained and untrained individuals. 6. Inter-individual differences in sport and exercise performance as well as adverse effects on sleep or feelings of anxiety following caffeine ingestion may be attributed to genetic variation associated with caffeine metabolism, and physical and psychological response. Other factors such as habitual caffeine intake also may play a role in between-individual response variation. 7. Caffeine has been shown to be ergogenic for cognitive function, including attention and vigilance, in most individuals. 8. Caffeine may improve cognitive and physical performance in some individuals under conditions of sleep deprivation. 9. The use of caffeine in conjunction with endurance exercise in the heat and at altitude is well supported when dosages range from 3 to 6 mg/kg and 4-6 mg/kg, respectively. 10. Alternative sources of caffeine such as caffeinated chewing gum, mouth rinses, energy gels and chews have been shown to improve performance, primarily in aerobic exercise. 11. Energy drinks and pre-workout supplements containing caffeine have been demonstrated to enhance both anaerobic and aerobic performance.


Assuntos
Cafeína/farmacologia , Exercício Físico/fisiologia , Sociedades Médicas , Fenômenos Fisiológicos da Nutrição Esportiva , Ciências da Nutrição e do Esporte , Ansiedade/induzido quimicamente , Ansiedade/genética , Desempenho Atlético/fisiologia , Cafeína/administração & dosagem , Cafeína/efeitos adversos , Cafeína/farmacocinética , Cápsulas , Goma de Mascar , Cognição/efeitos dos fármacos , Citocromo P-450 CYP1A2/genética , Citocromo P-450 CYP1A2/metabolismo , Doping nos Esportes , Cálculos da Dosagem de Medicamento , Bebidas Energéticas , Temperatura Alta , Humanos , Movimento/efeitos dos fármacos , Movimento/fisiologia , Força Muscular/efeitos dos fármacos , Força Muscular/fisiologia , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/fisiologia , Substâncias para Melhoria do Desempenho/farmacologia , Resistência Física/efeitos dos fármacos , Resistência Física/fisiologia , Desempenho Físico Funcional , Receptor A2A de Adenosina/genética , Receptor A2A de Adenosina/metabolismo , Sono/efeitos dos fármacos
6.
Eur J Sport Sci ; 21(10): 1403-1413, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-33043836

RESUMO

We examined the motor unit action potential amplitude versus recruitment threshold relationship (MUAPAMP-RT) as an indicator of MU-specific hypertrophy following high-intensity exercise training in females. Participants were assigned to either a high-intensity exercise (EX, n = 9) or control (CON, n = 18) condition and completed pre- (PRE) and post-testing (POST) during which maximal voluntary isometric leg extension strength (MVIT), vastus lateralis (VL) muscle cross sectional area (mCSA), whole leg skeletal muscle mass (SMMRL), and high-density surface EMG (HD-sEMG) signals were recorded from the VL during an isometric ramp contraction at 70% MVIT. The HD-sEMG signals were decomposed and yielded a MUAPAMP and an absolute (ABS; Nm) and normalized (NORM; %MVIC) RT for each MU. Individual MUAPAMP-RT slopes and intercepts were calculated for each subject. Changes in the pooled MUAPAMP-RT relationships for each group were also examined. Finally, relationships among individual changes in slopes of MUAPAMP-RT and individual changes in mCSA and SMMRL were examined. Training elicited increases in MVIT (+18%), mCSA (+12%), and mean and pooled slopes of MUAPAMP-RTNORM. The individual changes in slopes of both the MUAPAMP-RT relationships were moderately to strongly (r = 0.48-0.68) related to changes in mCSA and SMMRL. Eight-weeks of high-intensity exercise elicited increases in MUAPAMP-RT slope in females. Further, the observed change in slope was related to both VL mCSA and SMM of the tested leg. However, changes in slope for the MUAPAMP-RT relationship were more subdued when MUAPAMP was expressed relative to the absolute versus relative RT.


Assuntos
Potenciais de Ação , Treinamento Intervalado de Alta Intensidade , Músculo Esquelético/crescimento & desenvolvimento , Músculo Esquelético/fisiologia , Adolescente , Exercício Físico/fisiologia , Feminino , Humanos , Contração Isométrica , Perna (Membro) , Adulto Jovem
7.
Eur J Appl Physiol ; 121(2): 479-488, 2021 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-33123807

RESUMO

PURPOSE: To examine differences in the electromyographic vs torque (EMG-T) relationship, as well as muscle strength and indicators of muscle mass and quality between young versus postmenopausal females, and explore whether the potential differences in the EMG-T relationships could be explained by differences in muscle mass. METHODS: Thirty young (age = 20.7 ± 2.8 y) and 30 postmenopausal (age = 56.3 ± 4.7 y) females completed maximal isometric strength testing (MVIT) and isometric ramp contractions at 40% and 70% MVIT, during which electromyographic signals were collected to quantify the slopes (Slope40; Slope70) and intercepts (Intercept40; Intercept70) of the EMG-T relationships. Muscle mass and quality measurements were also completed. RESULTS: Postmenopausal females exhibited lower skeletal muscle mass (- 2.3 ± 1.5 kg), fat-free mass index (- 1.1 ± 0.7 kg·m-2), MVIT (- 17.1 ± 16.3 Nm), phase angle (- 0.5 ± 0.0°), muscle cross-sectional area (- 5.5 ± 1.1 cm2), muscle quality (- 0.1 ± 0.0 a.u), Slope40 (- 0.0003 ± 0.0002 mV·%MVIT-1), Slope70 (- 0.0003 ± 0.0002 mV·%MVIT-1), and had a higher echo intensity (+ 9.8 ± 2.8 a.u), Intercept40 (+ 0.001 ± 0.001 mV), and Intercept70 (+ 0.004 ± 0.003 mV) (p ≤ 0.001-0.04) than the young females. The EMG-T relationship variables were correlated with both muscle mass and quality after controlling for bodyweight. When controlling for muscle mass and bodyweight, group differences in the slopes of the EMG-T relationship and muscle strength were eliminated. CONCLUSION: Muscle mass and quality are primary contributors to the decrements in neuromuscular function observed in postmenopausal versus young females, and the preservation of muscle mass should be prioritized in the years leading up to, during, and immediately after menopause.


Assuntos
Peso Corporal/fisiologia , Músculo Esquelético/fisiologia , Pós-Menopausa/fisiologia , Adulto , Pesos e Medidas Corporais/métodos , Eletromiografia/métodos , Feminino , Humanos , Contração Isométrica/fisiologia , Pessoa de Meia-Idade , Força Muscular/fisiologia , Doenças Musculares/fisiopatologia , Torque , Adulto Jovem
8.
J Strength Cond Res ; 35(6): 1685-1692, 2021 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-30829982

RESUMO

ABSTRACT: Moghaddam, M, Estrada, CA, Muddle, TWD, Magrini, MA, Jenkins, NDM, and Jacobson, BH. Similar anaerobic and aerobic adaptations after 2 high-intensity interval training configurations: 10:5 s vs. 20:10 s work-to-rest ratio. J Strength Cond Res 35(6): 1685-1692, 2021-This study compares the effects of 2 high-intensity interval training (HIIT) configurations, a 10-5 vs. a 20-10 second work-to-rest ratio, on anaerobic and aerobic performance. Thirty-four individuals were randomly assigned to 10-5-HIIT (n = 17) and 20-10-HIIT (n = 17) groups to complete 6 cycles of 6 exercises, 3 days a week for 4 weeks. The 10-5-HIIT was performed with 10 s:5 s work-to-rest ratio with 1-minute recovery between cycles, while the 20-10-HIIT was performed with 20 s:10 s work-to-rest ratio followed by a 2-minute recovery. Anaerobic (i.e., peak power [PP], anaerobic capacity [AC], anaerobic power [AP], and total work [TW]) and aerobic fitness (i.e., time to exhaustion [TE], absolute V̇o2max [A-V̇o2max], relative V̇o2max [R-V̇o2max]) were measured with pre-training and post-training intervention. A significant main effect time was observed for both 10-5-HIIT and 20-10-HIIT (p < 0.05) in PP (9.2%, 5.7%); AC (14.9%, 8.6%); AP (9.0%, 6.2%); TW (15.1%, 8.5%); TE (4.3%, 5.5%); A-V̇o2max (9.4%, 8.9%); R-V̇o2max (8.5%, 8.2%), respectively. In conclusion, individuals may be able to achieve similar health benefits as 20-10-HIIT by performing 10-5-HIIT, despite exercising for 50% less total time. High-intensity interval training has been suggested as a "time-efficient" mode of exercise that can mitigate the most significant barrier to physical activity, "lack of time." Both 10-5-HIIT and 20-10-HIIT can induce performance adaptations to a similar extent. However, because of shorter time commitment, performing 10-5-HIIT at 10 s:5 s work-to-rest ratio may offer a shorter and equally efficient interval. Functional fitness training during HIIT protocols seems to be as beneficial as ergometer-based HIIT to improve anaerobic and aerobic performance.


Assuntos
Treinamento Intervalado de Alta Intensidade , Adaptação Fisiológica , Anaerobiose , Humanos , Consumo de Oxigênio , Descanso
9.
Nutr Res ; 83: 73-85, 2020 11.
Artigo em Inglês | MEDLINE | ID: mdl-33032071

RESUMO

This study examined whether an acute bout of resistance exercise (RE) attenuated postprandial responses to a high fat meal (HFM) similarly in younger versus older adult men, and probed relationships among skeletal muscle mass (SMM), age, the metabolic load index (MLI) response, and the improvement in the MLI elicited by RE versus CON. Eleven younger (24 ±â€¯4y) and 9 older (61 ±â€¯5y) men completed RE or control (CON) the night prior to a HFM. Before and 1, 3, and 5 hours after the HFM, blood triglycerides (TG), glucose (GLU), MLI, and cholesterol concentrations were quantified. Following a 7 ±â€¯1-day washout period, participants returned and completed the opposite condition. Independent of age, TGs were 32.1 ±â€¯27.1 mg/dL and 52.7 ±â€¯26.8 mg/dL lower in RE than CON at 3 and 5 hours, respectively. MLI was also 24.3 to 56.9 mg/dL lower in RE than CON from 1 to 5 hours post-meal independent of age. The TG and MLI area under the curves (AUCs) were 15% to 31% lower in RE than CON. The GLU response was greater in the older than younger men at 1 to 5 hours post-meal. Moreover, the average GLU response was 5.6 ±â€¯2.5 mg/dL lower in RE versus CON and was inversely related to SMM across the sample (r = -0.615). However, age, volume, or SMM were not related to the MLIAUC, nor to the improvement elicited by RE. Therefore, although the older men displayed a greater postprandial glucose response than the younger men, RE attenuated the postprandial metabolic response to a HFM similarly in younger and older men.


Assuntos
Dieta Hiperlipídica , Gorduras na Dieta/metabolismo , Período Pós-Prandial , Treinamento de Força , Adulto , Idoso , Envelhecimento , Área Sob a Curva , Glicemia/metabolismo , Colesterol/sangue , Estudos Cross-Over , Humanos , Masculino , Refeições , Pessoa de Meia-Idade , Músculo Esquelético/anatomia & histologia , Triglicerídeos/sangue , Adulto Jovem
10.
Int J Sport Nutr Exerc Metab ; : 1-8, 2020 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-32908019

RESUMO

The consumption of a high-fat meal can induce postprandial lipemia and endothelial dysfunction. The authors assessed the impact of age and physical activity on metabolic and vascular outcomes following meal consumption in healthy adults. The authors recruited four groups: younger active (age 22.1 ± 1.4 years; n = 9), younger inactive (age 22.6 ± 3.7 years; n = 8), older active (age 68.4 ± 7.7 years; n = 8), and older inactive (age 67.7 ± 7.2 years; n = 7). The metabolic outcomes were measured at the baseline and hourly for 6 hr post high-fat meal consumption (12 kcal/kg; 63% fat). Flow-mediated dilation was measured at the baseline, 2 hr, and 4 hr postmeal. The total area under the curve for triglycerides was significantly lower in the more active groups, but did not differ based on age (younger active = 6.5 ± 1.4 mmol/L × 6 hr, younger inactive = 11.7 ± 4.8, older active = 6.8 ± 2.7, older inactive = 12.1 ± 1.7; p = .0004). After adjusting for artery diameter, flow-mediated dilation differed between groups at the baseline (younger active = 4.8 ± 1.6%, younger inactive = 2.5 ± 0.5, older active = 3.4 ± 0.9, older inactive = 2.2 ± 0.4; p < .001) and decreased significantly across groups 4 hr postmeal (mean difference = 0.82; 95% CI [0.02, 1.6]; p = .04). These findings highlight the beneficial effect of regular physical activity on postprandial lipemia, independent of age.

11.
J Musculoskelet Neuronal Interact ; 20(1): 77-87, 2020 03 03.
Artigo em Inglês | MEDLINE | ID: mdl-32131371

RESUMO

OBJECTIVES: This study examined the time course of changes and patterns of responses in electromyographic amplitude (EMG AMP) and EMG mean power frequency (MPF) for the superficial quadriceps muscles during exhaustive treadmill runs within the severe exercise intensity zones (SIZ1 and SIZ2). METHODS: The EMG signals for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) as well as times to exhaustion (Tlim) were recorded in ten runners during two exhaustive treadmill runs (SIZ1 and SIZ2). The composite and individual responses were compared among muscles and between intensities. RESULTS: The composite patterns of responses in EMG AMP (linear, quadratic, and cubic increases; r2/R2=0.684-0.848) and EMG MPF (linear, quadratic, and cubic decreases; r2/R2=0.648 - 0.852) for the VL and RF were consistent with neuromuscular fatigue in both zones, but those for the VM were not (quadratic, cubic, and non-significant relationships with responses near baseline). The RF tended to demonstrate greater fatigue (EMG MPF decreased from 80-100% Tlim). There was large inter-individual variability (only 10-60% of responses consistent with composite) in response to fatiguing treadmill running. CONCLUSIONS: The current findings support the examination and characterization of neuromuscular fatigue on an intensity, muscle, and subject-by-subject basis.


Assuntos
Teste de Esforço/métodos , Fadiga Muscular/fisiologia , Junção Neuromuscular/fisiologia , Músculo Quadríceps/fisiologia , Corrida/fisiologia , Adulto , Eletromiografia/métodos , Feminino , Humanos , Masculino , Adulto Jovem
12.
J Appl Biomech ; : 1-8, 2020 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-32143191

RESUMO

Pitch velocity (PV) is important for pitching success, and the pelvis and trunk likely influence pitch performance. The purposes of this study were to examine the differences in pelvis and trunk kinetics and kinematics in professional baseball pitchers who throw at lower versus higher velocities (HVPs) and to examine the relationships among pelvis and trunk kinetics and kinematics and PV during each phase of the pitch delivery. The pitch velocity, pelvis and trunk peak angular velocities, kinetic energies and torques, and elbow and shoulder loads were compared among HVPs (n = 71; PV ≥ 40.2 m/s) and lower velocities pitchers (n = 78; PV < 39.8 m/s), as were trunk and pelvis rotation, flexion, and obliquity among 7 phases of the pitching delivery. Relationships among the kinetic and kinematic variables and PVs were examined. Higher velocity pitchers achieved greater upper trunk rotation at hand separation (+7.2°, P < .001) and elbow extension (+5.81°, P = .002) and were able to generate greater upper trunk angular velocities (+36.6 m/s, P = .01) compared with lower velocity pitcher. Trunk angular velocity (r = .29) and upper trunk rotation at hand separation (r = .18) and foot contact (r = .17) were weakly related to PV. Therefore, HVPs rotate their upper trunk to a greater degree during the early phases of the pitching motion and subsequently generate greater trunk angular velocities and PV.

13.
J Strength Cond Res ; 34(4): 1184-1187, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30418328

RESUMO

McKay, BD, Miramonti, AA, Gillen, ZM, Leutzinger, TJ, Mendez, AI, Jenkins, NDM, and Cramer, JT. Normative reference values for high school-aged American football players: Proagility drill and 40-yard dash split times. J Strength Cond Res 34(4): 1184-1187, 2020-The purpose of this short report was to provide test- and position-specific normative reference values for the 10- and 20-yd split times (10YD and 20YD) during the 40-yd dash (40YD) as well as 10-yd split times during the proagility drill (PA) based on a large, nationally representative sample of high school-aged American football players in their freshman, sophomore, and junior classes. Cross-sectional performance data were obtained from 12 different high school American football recruiting combines between March 7, 2015, and January 9, 2016, across the United States. The sample included (n = 7,478) high school-aged American football athletes in their freshman (n = 1,185), sophomore (n = 2,514), and junior (n = 3,779) classes. Each player self-classified their American football positions as defensive back, defensive end, defensive linemen, linebacker, offensive linemen (OL), quarterback (QB), running back, tight end, or wide receiver. The results of the freshman, sophomore, and junior class were aggregated to generate test- and position-specific normative values. Mean differences were found among classes for all positions and all measurements (p ≤ 0.05) except for OL and QB PA split time (p > 0.05). Greater percent differences for all 3 variables were observed between freshman and sophomore years than between sophomore and junior years. These normative reference values will be useful for athletes, parents, coaches, and high school strength and conditioning professionals to set realistic goals for young American football athletes.


Assuntos
Desempenho Atlético/fisiologia , Futebol Americano/fisiologia , Corrida/fisiologia , Adolescente , Atletas , Pesos e Medidas Corporais , Estudos Transversais , Humanos , Masculino , Valores de Referência , Estados Unidos
14.
J Strength Cond Res ; 34(10): 2849-2856, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-29489728

RESUMO

McKay, BD, Miramonti, AA, Gillen, ZM, Leutzinger, TJ, Mendez, AI, Jenkins, NDM, and Cramer, JT. Normative reference values for high school-aged American football players. J Strength Cond Res 34(10): 2849-2856, 2020-The purpose of the present report was to provide test- and position-specific normative reference values for combine test results based on a large, nationally representative sample of high school-aged American football players in their freshman, sophomore, and junior classes. Cross-sectional anthropometric and performance data were obtained from 12 different high school American football recruiting combines between March 7, 2015, and January 9, 2016, across the United States. Subjects included a sample (n = 7,478) of high school-aged American football athletes in their junior (n = 3,779), sophomore (n = 2,514), and freshman (n = 1,185) classes. The database included combine date, school state, position, class, height, body mass (BM), 40-yard dash, pro-agility, 3-cone, vertical jump, broad jump, and power push-up. Each player self-classified their American football positions as defensive back, defensive end, defensive linemen, linebacker, offensive linemen, quarterback, running back, tight end (TE), or wide receiver. Test- and position-specific normative values were generated by aggregating data from freshman, sophomore, and junior classes. Mean differences were found among classes for all positions and all measurements (p ≤ 0.05), except for TE BM (p > 0.05). Greater differences for all variables were observed from freshman to sophomore classes than from sophomore to junior classes. These normative reference values may provide realistic comparisons and evaluations in performance for young American football players, parents, and coaches with collegiate football aspirations. High school strength and conditioning professionals should use these norms to set attainable goals and reward accomplishments for young football players.


Assuntos
Atletas , Desempenho Atlético/fisiologia , Desempenho Atlético/normas , Futebol Americano/fisiologia , Futebol Americano/normas , Adolescente , Adulto , Antropometria , Estatura , Índice de Massa Corporal , Estudos Transversais , Teste de Esforço , Humanos , Masculino , Valores de Referência , Corrida/fisiologia , Corrida/normas , Estados Unidos , Universidades
15.
J Strength Cond Res ; 2019 Aug 23.
Artigo em Inglês | MEDLINE | ID: mdl-31453941

RESUMO

Jenkins, NDM, Miramonti, AA, Hill, EC, Smith, CM, Cochrane-Snyman, KC, Housh, TJ, and Cramer, JT. Mechanomyographic amplitude is sensitive to load-dependent neuromuscular adaptations in response to resistance training. J Strength Cond Res XX(X): 000-000, 2019-We examined the sensitivity of the mechanomyographic amplitude (MMGRMS) and frequency (MMGMPF) vs. torque relationships to load-dependent neuromuscular adaptations in response to 6 weeks of higher- vs. lower-load resistance training. Twenty-five men (age = 22.8 ± 4.6 years) were randomly assigned to either a high- (n = 13) or low-load (n = 12) training group and completed 6 weeks of leg extension resistance training at 80 or 30% 1RM. Before and after 3 and 6 weeks of training, mechanomyography signals were recorded during isometric contractions at target torques equal to 10-100% of the subjects' baseline maximal strength to quantify MMGRMS and MMGMPF vs. torque relationships. MMGRMS decreased from Baseline to weeks 3 and 6 in the high-load, but not low-load group, and was dependent on the muscle and intensity of contraction examined. Consequently, MMGRMS was generally lower in the high- than low-load group at weeks 3 and 6, and these differences were most apparent in the vastus lateralis (VL) and rectus femoris muscles at higher contraction intensities. MMGMPF was greater in the high- than low-load training group independent of time or muscle. The MMGRMS vs. torque relationship was sensitive to load-dependent, muscle-specific neuromuscular adaptations and suggest reductions in neuromuscular activation to produce the same absolute submaximal torques after training with high, but not low loads.

16.
Eur J Appl Physiol ; 119(9): 2083-2094, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31372804

RESUMO

PURPOSE: The mediators of the perception of effort during exercise are still unclear. The aim of the present study was to examine physiological responses during runs using a rating of perceived exertion (RPE)-clamp model at the RPE corresponding to the gas exchange threshold (RPEGET) and 15% above GET (RPEGET+15%) to identify potential mediators and performance applications for RPE during treadmill running. METHODS: Twenty-one runners ([Formula: see text]max = 51.7 ± 8.3 ml kg-1 min-1) performed a graded exercise test to determine maximal oxygen consumption and the RPE associated with GET and GET + 15% followed by randomized 60 min RPE-clamp runs at RPEGET and RPEGET+15%. Mean differences for [Formula: see text], heart rate (HR), minute ventilation ([Formula: see text]), respiratory frequency ([Formula: see text], respiratory exchange ratio (RER), and velocity were compared across each run. RESULTS: After minute 14, [Formula: see text], RER and velocity did not differ across conditions, but decreased across time (p < 0.05). There was a significant (p < 0.05) condition × time interaction for [Formula: see text], where values were significantly higher during RPE-clamp runs at RPEGET+15% and decreased across time in both conditions. There were no differences across condition or time for HR, and only small difference between conditions for [Formula: see text]. CONCLUSIONS: HR and [Formula: see text] may play a role in mediating the perception of effort, while [Formula: see text], RER, and [Formula: see text] may not. Although HR and [Formula: see text] may mediate the maintenance of a perceptual intensity, they may not be sensitive to differentiate perceptual intensities at GET and GET + 15%. Thus, prescribing exercise using an RPE-clamp model may only reflect a sustainable [Formula: see text] within the moderate intensity domain.


Assuntos
Exercício Físico/fisiologia , Esforço Físico/fisiologia , Corrida/fisiologia , Adulto , Teste de Esforço/métodos , Terapia por Exercício/métodos , Feminino , Frequência Cardíaca/fisiologia , Humanos , Masculino , Consumo de Oxigênio/fisiologia , Troca Gasosa Pulmonar/fisiologia , Taxa Respiratória/fisiologia , Ventilação/métodos , Adulto Jovem
17.
J Electromyogr Kinesiol ; 48: 121-127, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31344640

RESUMO

OBJECTIVE: The purpose was two-fold: (1) to examine differences in maximal voluntary isometric torque (MVIT) production, and electromyographic signal amplitude (EMGAMP) and mean power frequency (EMGMPF) values obtained during traditional (MVICTRAD), rapid (MVICRAPID), and ramp (MVICRAMP) maximal voluntary isometric contractions, and (2) to determine if there were differences in the reliability of MVIT, EMGAMP and EMGMPF among the three MVIC types. APPROACH: Twenty-two young males and females completed MVICTRAD, MVICRAPID, and MVICRAMP muscle actions on two separate visits separated by 48 h. During all MVICs, MVIT and EMGAMP and EMGMPF of the vastus lateralis (VL) and rectus femoris (RF) were quantified. MAIN RESULTS: MVIT was greater during MVICTRAD and MVICRAPID than during MVITRAMP (both p < 0.001). VL and RF EMGAMP were greater during MVICRAMP than during MVICRAPID (p = 0.02 and 0.004). For EMGMPF, there were no significant differences among MVIC types. Although all MVIC types generally resulted in reliable measurements of MVIT and EMGAMP, reliability was stronger for EMGMPF quantified during the MVICRAMP. SIGNIFICANCE: Investigators may choose MVIC type based on preference or equipment availability. However, investigators should note that MVICRAMP contractions will likely yield the greatest EMGAMP values and more reliable measurements of VL and RF EMGMPF.


Assuntos
Eletromiografia/métodos , Contração Isométrica , Adulto , Eletromiografia/normas , Feminino , Humanos , Masculino , Músculo Esquelético/fisiologia , Valores de Referência , Reprodutibilidade dos Testes , Torque
18.
J Strength Cond Res ; 33(4): 1007-1019, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30789573

RESUMO

Muddle, TWD, Magrini, MA, Colquhoun, RJ, Luera, MJ, Tomko, PM, and Jenkins, NDM. Impact of fatiguing, submaximal high- vs. low-torque isometric exercise on acute muscle swelling, and echo intensity in resistance-trained men. J Strength Cond Res 33(4): 1007-1019, 2019-To evaluate the effects of repeated, fatiguing isometric knee extension contractions performed at high-torque (HT) vs. low-torque (LT) maximal voluntary isometric contraction (MVIC) on acute muscle swelling, and echo intensity (EI) of the rectus femoris (RF) and vastus lateralis (VL) muscles in resistance-trained males. Twenty-two resistance-trained men performed either HT (70% MVIC) or LT (30% MVIC) isometric contractions to fatigue on separate days. Before and after exercise, muscle cross-sectional area (mCSA) and EI of the RF and VL were assessed through ultrasound. Muscle cross-sectional area and EI (collapsed across muscle) increased similarly after HT (mean ± 95% confidence interval: mCSAΔ: 3.52 ± 0.52 cm; EIΔ: 4.58 ± 1.65 au) and LT (mCSAΔ: 3.61 ± 0.59 cm; EIΔ: 3.30 ± 1.36 au) exercise. No relationships between mCSAΔ and time to task failure (TTF), normalized MVIC, or the tension-time integral were observed during either HT or LT exercise. During both conditions, EIΔ was related to TTF (HT: r = 0.44; LT: r = 0.66) and normalized MVIC (HT: r = -0.60; LT: r = -0.57). These results suggest that acute muscle swelling and increased EI observed in response to intermittent, submaximal, fatiguing isometric exercise are similar for the RF and VL and are not dependent on the torque-level or tension-time integral when exercise is performed to failure. Factors such as the duration of time performing exercise and relative muscle strength may influence the magnitude of change in EI, but not acute muscle swelling, during intermittent fatiguing isometric exercise.


Assuntos
Edema/etiologia , Exercício Físico/fisiologia , Contração Isométrica/fisiologia , Fadiga Muscular/fisiologia , Músculo Quadríceps/fisiologia , Adulto , Humanos , Masculino , Esforço Físico/fisiologia , Músculo Quadríceps/diagnóstico por imagem , Distribuição Aleatória , Treinamento de Força , Torque , Ultrassonografia , Adulto Jovem
19.
J Neurophysiol ; 120(6): 3131-3139, 2018 12 01.
Artigo em Inglês | MEDLINE | ID: mdl-30355024

RESUMO

Decomposition of the surface electromyographic (sEMG) signal is commonly used to examine motor unit (MU) firing behavior. However, the intra- and inter-day reliability of these measurements has yet to be quantified or reported. This investigation 1) examined the effect of input excitation on the mean firing rate (MFR) vs. recruitment threshold (RT) relationship and 2) determined the inter- and intra-day reliability of the MFR vs. RT relationship at 30%, 50%, and 70% of maximum voluntary isometric strength (MVIC). Twenty-eight healthy males (23 ± 3 yr) completed two experimental visits, during which they performed MVIC testing and isometric ramp contractions at 30%, 50%, and 70% MVIC. sEMG signals were recorded from the vastus lateralis during the ramp contractions and decomposed to establish the MFR vs. RT relationship for the detected MUs. Intra- and inter-day reliability was then established for the slopes and y-intercepts of the MFR vs. RT relationship at each contraction intensity. All participants displayed significant MFR vs. RT relationships ( r range: -0.662 to -0.999; P ≤ 0.001-0.006). Intra- and inter-day intraclass correlation coefficients (ICCs) ranged from 0.766-0.824 and 0.867-0.919 for the slopes and from 0.780-0.915 and 0.804-0.927 for the y-intercepts, respectively. Furthermore, the slope coefficient was significantly greater at 70% than at 30% MVIC, and the y-intercepts increased with increasing contraction intensities. Changes in input excitation to the MU pool alter the magnitude, but not the reliability, of the slopes and y-intercepts of the MFR vs. RT relationship. NEW & NOTEWORTHY The firing behavior of the motor unit (MU) pool is often characterized using the mean firing rate vs. recruitment threshold relationship of the active MUs. Although this relationship has been widely used, this is the first study to report the effects of input excitation (contraction intensity) on the intra- and inter-day reliability of this relationship. The criteria used for MU analysis and the model utilized in this study allow for generalization to outside investigators and laboratories.


Assuntos
Músculo Esquelético/fisiologia , Recrutamento Neurofisiológico , Adulto , Eletromiografia/normas , Potencial Evocado Motor , Humanos , Masculino , Músculo Esquelético/inervação
20.
Exp Physiol ; 103(12): 1645-1655, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30267546

RESUMO

NEW FINDINGS: What is the central question of this study? Does a common genetic variant in the ß2 -adrenergic receptor (ß2 -AR) have effects on skeletal muscle function in young, healthy men? What is the main finding and its importance? This study provides preliminary evidence that ß2 -AR Arg16Gly genotype has a significant effect on fat-free mass, muscle strength and motor unit behaviour in recreationally trained men. These data might have important clinical and exercise-related implications. For example, ß2 -AR (rs1042713) genotype might influence the responsiveness of skeletal muscle to clinical or exercise-based interventions or ß-AR agonist treatment. ABSTRACT: This study explored whether the ß2 -adrenergic receptor (ß2 -AR) single nucleotide polymorphism at amino acid 16 (Arg16Gly) has functional effects on skeletal muscle mass, torque production and motor unit behaviour in young, healthy men. Twenty-eight recreationally active men (mean ± SD 23.1 ± 1.3 years of age) were genotyped for Arg16Gly polymorphisms of ß2 -AR as arginine homozygous (ArgArg; n = 5), glycine homozygous (GlyGly; n = 11) or arginine-glycine heterozygous (ArgGly; n = 12). The participants then completed body composition testing, assessments of leg extensor size and echo intensity, and evoked and voluntary isometric leg-extension muscle actions. During the evoked muscle actions, peak twitch torque, peak rate of torque development and peak relaxation rate were assessed. During the voluntary muscle actions, maximal voluntary isometric (MVIC) strength was assessed, and surface EMG signals were obtained during submaximal isometric muscle actions and later decomposed to examine motor unit firing behaviour. Fat-free mass and MVIC strength were greater (P = 0.004, d = 1.74 and P = 0.026, d = 1.10, respectively) in those expressing the GlyGly versus ArgArg allele. The slope of the mean firing rate versus recruitment threshold relationship was more negative in the GlyGly than the ArgArg allele carriers (P = 0.012, d = 1.68) at 50% MVIC, but was less negative in GlyGly and ArgGly versus ArgArg allele carriers (P = 0.013 and 0.016, respectively; d = 1.34 and 1.20, respectively) at 70% MVIC. These data provide preliminary evidence that ß2 -AR Arg16Gly genotype has a significant effect on fat-free mass, muscle strength and motor unit behaviour in humans.


Assuntos
Arginina/genética , Glicina/genética , Neurônios Motores/fisiologia , Força Muscular/genética , Músculo Esquelético/fisiologia , Polimorfismo Genético/genética , Receptores Adrenérgicos beta 2/genética , Adulto , Alelos , Eletromiografia/métodos , Genótipo , Humanos , Masculino , Neurônios Motores/metabolismo , Força Muscular/fisiologia , Músculo Esquelético/metabolismo , Torque , Adulto Jovem
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