Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 18 de 18
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
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 Park Relat Disord ; 5: 100103, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-34430844

RESUMO

Introduction: It is widely accepted that pathophysiological changes to the central nervous system of persons with Parkinson's disease (PD) result in negative effects on motor function. However, less information is known regarding the pathology of PD on skeletal muscle. The purpose of this study was to determine the effect of a fatiguing isometric knee extension protocol on muscle mechanics using evoked twitch contractions in persons with PD and in non-impaired older adults (OLD). Methods: Evoked twitch contractions were examined during a fatiguing protocol in PD (66 ± 9 yr, n = 8) and OLD (65 ± 10 yr, n = 5). Participants performed 5-sec maximal isometric voluntary contractions of the quadriceps femoris with 5-sec rest for 3-min. Every 30-sec during rest intervals, a maximal transcutaneous electrical stimulus was administered to the quadriceps femoris to quantify evoked peak twitch torque (pTT), peak relaxation rate (pRR), and peak rate of torque development (pRTD). Results: A large effect of voluntary fatigue (%decline) was observed (g = 1.58). There were no significant differences in pTT (p = 0.09; 95% CI:-3.6, 0.28) or pRR (p = 0.11; 95% CI:-31, 3.6). However, the slope decline of pRTD in OLD (-35.4 ± 24.7) was greater than PD (-11.5 ± 11.4; p = 0.03), indicating that skeletal muscle in persons with PD is less fatigable compared to non-impaired older adults. Conclusion: The rate, not the maximum capacity, of torque generation of the muscle during a fatiguing knee extension protocol was affected by PD. Future studies are warranted to identify the mechanism(s) responsible for the observed differences in skeletal muscle contractile characteristics and potential myofiber distribution variation in PD.

3.
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
4.
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
5.
Eur J Appl Physiol ; 119(6): 1313-1322, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30874884

RESUMO

PURPOSE: The purpose of this study was to determine the effect of age on the cross-education of rapid and maximal contractile properties for the knee extensors. METHODS: Young (n = 10; age = 21.1 ± 1.7 years) and older (n = 10; age = 65.3 ± 8.3 years) males performed unilateral isokinetic resistance training (RT) of the knee extensors for 4 weeks. Maximal voluntary isokinetic (45° s-1 and 300° s-1) and isometric testing was conducted for the trained and untrained leg before and after RT. Peak torque (PT) and acceleration were obtained from isokinetic testing as well as torque at 30 ms (TQ30) and 100 ms (TQ100) from the 45° s-1 contraction. PT and rate of torque development were recorded from the isometric contractions. RESULTS: Independent of age, isometric PT (10.1%; p = 0.006) as well as PT and acceleration at 300° s-1 (6.7%; p = 0.008 and 4.0%; p = 0.016, respectively) increased in the untrained leg. At 45° s-1, acceleration was increased (3.6%; p = 0.021), but PT remained unchanged (p = 0.227). TQ100 increased similarly between groups (4.5%; p = 0.014), but TQ30 increased only in the older group (9.5%; p = 0.022). CONCLUSIONS: Cross-education of rapid and maximal contractile parameters can be achieved early during unilateral RT independent of age. These findings indicate the potential for particular unilateral RT protocols to be used for older adults in rehabilitative settings to offset disuse-related reductions in contractile function, which are most dramatic in this population.


Assuntos
Adaptação Fisiológica , Envelhecimento/fisiologia , Contração Isométrica , Força Muscular , Idoso , Humanos , Masculino , Pessoa de Meia-Idade , Músculo Esquelético/crescimento & desenvolvimento , Músculo Esquelético/fisiologia , Adulto Jovem
6.
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
7.
J Aging Phys Act ; 27(1): 1-8, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-29485309

RESUMO

This study examined the effects of unilateral resistance training (RT) on maximal velocity parameters in the ipsilateral and contralateral legs in young and older males. Young (n = 22; age = 21.55 ± 2.23 years) and older (n = 20; age = 65.10 ± 9.65 years) males were assigned to training or control groups. Unilateral isokinetic RT of the knee extensors was performed for 4 weeks. Peak velocity and acceleration were identified during a dynamic maximal voluntary contraction before (PRE), at Week 2 (MID), and after Week 4 (POST) of RT. Age-independent increases in peak velocity (1.5%) and acceleration (4.5%) were demonstrated at POST for the trained leg. For the untrained leg, acceleration increased (4.3%) at POST similarly between training groups. These findings provide evidence for the high degree of neuromuscular plasticity, regardless of age, during the early phase of RT, and the potential for cross education of acceleration.


Assuntos
Envelhecimento/fisiologia , Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Treinamento de Força , Adaptação Fisiológica , Idoso , Humanos , Articulação do Joelho/fisiologia , Masculino , Pessoa de Meia-Idade , Contração Muscular/fisiologia , Adulto Jovem
8.
Ultrasound ; 26(4): 214-221, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30479636

RESUMO

Introduction: The purpose of this investigation was to: (1) to determine the reliability of rectus femoris muscle cross-sectional area and echo intensity obtained using panoramic ultrasound imaging during seated and supine lying positions before and after a 5-minute rest period and (2) to determine the influence of body position and rest period on the magnitude of rectus femoris muscle cross-sectional area and echo intensity measurements. Methods: A total of 23 males and females (age = 21.5 ± 1.9 years) visited the laboratory on two separate occasions. During each visit, panoramic ultrasound images of the rectus femoris were obtained in both a seated and a supine position before (T1) and after a 5-minute (T2) rest period to quantify any potential changes in either muscle cross-sectional area and/or echo intensity. Results: None of the muscle cross-sectional area or echo intensity measurements exhibited systematic variability, and the ICCs were 0.98-0.99 and 0.88-0.91, and the coefficients of variation were ≤ 3.9% and ≤ 8.2% for muscle cross-sectional area and echo intensity, respectively. Our results indicated that muscle cross-sectional area was greater in the seated than supine position, whereas echo intensity was greater in the supine position. Further, echo intensity increased in the seated position from T1 to T2. Conclusion: Both rectus femoris muscle cross-sectional area and echo intensity may be reliably measured in either a seated or supine lying position before or after a 5-minute rest period. Aside from echo intensity in the seated position, rest period had no influence on the magnitude of muscle cross-sectional area or echo intensity. Comparison of muscle cross-sectional area values that are obtained in different body positions is ill-advised.

9.
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
10.
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
11.
J Electromyogr Kinesiol ; 42: 111-116, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30015134

RESUMO

OBJECTIVE: To determine if maximal isometric contraction (MVIC) method (i.e., ramp (MVICRAMP) versus traditional MVIC) influences (1) maximal voluntary isometric torque (MVIT) production of the knee extensors, (2) electromyographic signal amplitude (EMGAMP), and (3) EMG mean power frequency (EMGMPF) of the rectus femoris and vastus lateralis in moderately-to highly-activated subjects. We hypothesized that EMGAMP would be greater during the MVICRAMP than MVIC muscle contractions, but that there would be no difference in MVIT. APPROACH: Twenty-five males (23.4 ±â€¯3.4 y; % voluntary activation = 93.9 ±â€¯5.1%) visited the laboratory and completed MVICRAMPs and MVICs. During all contractions, leg extensor torque and sEMG signals from the vastus lateralis (VL) and rectus femoris (RF) were recorded. MAIN RESULTS: There was no significant difference in the MVIT produced (p = 0.65) or in EMGMPF (p = 0.052) during MVICRAMP versus MVIC. However, EMGAMP was 18.1% higher during the MVICRAMP than MVIC (p = 0.004). SIGNIFICANCE: Maximal isometric muscle contraction method significantly influenced EMGAMP, and had a moderate effect on EMGMPF (d = 0.49). Investigators who utilize MVICs to determine maximal EMG signal amplitude and frequency to normalize their EMG signals should be aware of these differences.


Assuntos
Eletromiografia/métodos , Contração Isométrica , Joelho/fisiologia , Adulto , Eletromiografia/normas , Humanos , Masculino , Músculo Esquelético/fisiologia , Valores de Referência , Torque
12.
J Strength Cond Res ; 32(8): 2348-2355, 2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-30036265

RESUMO

Magrini, MA, Colquhoun, RJ, Sellers, JH, Conchola, EC, Hester, GM, Thiele, RM, Pope, ZK, and Smith, DB. Can squat jump performance differentiate starters vs. nonstarters in division I female soccer players? J Strength Cond Res 32(8): 2348-2355, 2018-Although soccer is predominately an endurance sport, high velocity movements may be an important indicator of athletic success. The purpose of this investigation was to establish whether squat jumps (SJs) can differentiate starters from nonstarters with a female collegiate division I soccer team. Eighteen female division I soccer athletes were separated into 2 groups: 9 starters (age: 19.5 ± 1.0; mass = 64.8 ± 11.5 kg; height = 167.5 ± 7.7 cm; games started = 18.2 ± 4.7; and minutes played = 1633.8 ± 478.2 minutes) and 9 nonstarters (age: 19.4 ± 1.4 years; mass = 63.3 ± 4.2 kg; height = 164.7 ± 6.8 cm; games started 0.7 ± 1.3; and minutes played 158.2 ± 269.3 minutes). Each athlete performed 3 maximal SJs at a starting knee angle of 110° without arm swing. Each participant's SJ height, mean power (MP), peak power (PP), mean velocity (MV), and peak velocity (PV) were measured during each attempt by a linear position transducer. No statistically significant differences (p ≥ 0.05) in MP and PP between the starters and nonstarters were observed. However, starters performed significantly better than nonstarters in SJ height (p = 0.002), MV (p = 0.025), and PV (p = 0.015). In addition, SJ height was strongly correlated with MV (r = 0.628) and PV (r = 0.647). These findings suggest that SJ height, MV, and PV may be important variables for discriminating differences between starters and nonstarters in division I female soccer athletes and a strong indicator of explosive performance.


Assuntos
Desempenho Atlético/fisiologia , Movimento/fisiologia , Músculo Esquelético/fisiologia , Futebol/fisiologia , Universidades , Adolescente , Teste de Esforço , Feminino , Humanos , Força Muscular , Adulto Jovem
13.
Physiol Rep ; 6(8): e13675, 2018 04.
Artigo em Inglês | MEDLINE | ID: mdl-29673119

RESUMO

The purpose of this investigation was to evaluate the effects of repeated, high- (HT: 70% MVIC) versus low-torque (LT: 30% MVIC) isometric exercise performed to failure on motor unit (MU) recruitment and firing behavior of the vastus lateralis. Eighteen resistance-trained males (23.1 ± 3.8 years) completed familiarization, followed by separate experimental sessions in which they completed either HT or LT exercise to failure in random order. LT exercise resulted in a greater time to task failure and a more dramatic decline in the muscle's force capacity, but the total work completed was similar for HT and LT exercise. An examination of the firing trains from 4670 MUs recorded during exercise revealed that firing rates generally increased during HT and LT exercise, but were higher during HT than LT exercise. Furthermore, recruitment thresholds (RT) did not significantly change during HT exercise, whereas the RT of the smallest MUs increased and the RT for the moderate to large MUs decreased during LT exercise. Both HT and LT exercise resulted in the recruitment of additional higher threshold MUs in order to maintain torque production. However, throughout exercise, HT required the recruitment of larger MUs than did LT exercise. In a few cases, however, MUs were recruited by individuals during LT exercise that were similar in size and original (pre) RT to those detected during HT exercise. Thus, the ability to achieve full MU recruitment during LT exercise may be dependent on the subject. Consequently, our data emphasize the task and subject dependency of muscle fatigue.


Assuntos
Potenciais de Ação/fisiologia , Exercício Físico/fisiologia , Contração Isométrica/fisiologia , Neurônios Motores/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Recrutamento Neurofisiológico/fisiologia , Adulto , Humanos , Masculino , Torque , Adulto Jovem
14.
Physiol Rep ; 6(5)2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29527830

RESUMO

Previous investigations have reported a relationship between skeletal muscle phenotype and motor unit (MU) firing parameters during submaximal contractions. The purpose of the current investigation, however, was to examine the relationships between motor unit firing behavior during a maximal voluntary contraction, Myosin Heavy Chain (MHC) isoform content, and various molecular neuromuscular targets of the vastus lateralis (VL) muscle in resistance-trained men. Ten resistance-trained males completed a trapezoidal ramp contraction up to 100% of their maximal voluntary isometric strength (MVIC). Surface electromyography was recorded from the VL using a multichannel electrode array and decomposed to examine the firing characteristics of individual MUs. A skeletal muscle biopsy of the VL was also collected from each subject. Regression analyses were performed to identify relationships between type II fiber area and the slopes and/or intercepts of the mean firing rate (FRMEAN ) versus recruitment threshold (RT), max firing rate (FRMAX ) versus RT, and RT versus MU action potential amplitude (MUAPPP ) relationships. There were significant inverse relationships between type II fiber area and the y-intercept of the FR versus RT relationship (P < 0.05). Additionally, strong relationships (r > 0.5) were found between type II fiber area and FRMEAN versus RT slope and RT versus MUAPPP slope and intercept. These data further support the hypothesis that skeletal muscle phenotype is related to MU behavior during isometric contraction. However, our data, in concert with previous investigations, may suggest that these relationships are influenced by the intensity of the contraction.


Assuntos
Contração Isométrica , Músculo Esquelético/fisiologia , Recrutamento Neurofisiológico , Potencial Evocado Motor , Humanos , Masculino , Músculo Esquelético/metabolismo , Cadeias Pesadas de Miosina/metabolismo , Fenótipo , Adulto Jovem
15.
Orthop J Sports Med ; 6(3): 2325967118760780, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29581995

RESUMO

Background: Elbow injury rates among baseball pitchers are rapidly rising. However, this increase has been most dramatic among high school (HS) pitchers. Purpose: To examine pitch velocity and the kinetic and kinematic characteristics of HS versus professional (PRO) pitchers to identify potential differences that may play a role in the increased risk of ulnar collateral ligament injury in youth pitchers. Study Design: Controlled laboratory study. Methods: A total of 37 HS (mean ± SD: age, 16 ± 1 years) and 40 PRO (age, 21 ± 2 years) baseball pitchers completed maximal-effort baseball pitches during a single testing session, from which pitch velocity (PV), absolute and normalized elbow varus torque (EVTA and EVTN, respectively) during arm cocking and at maximum shoulder external rotation (MER), and 8 other elbow and shoulder torques or forces and rotational kinematics of the pelvis and trunk were analyzed, recorded, and compared. Results: PV was greater in PRO than HS athletes; EVTA was greater in PRO than HS athletes during arm cocking and at MER; but EVTN was similar during arm cocking and greater in HS than PRO athletes at MER. In PRO athletes, PV was not related to EVTA during arm cocking or MER (r = 0.01-0.05). Furthermore, in PRO athletes, EVTA during arm cocking and at MER were inversely related to upper trunk rotation at hand separation and foot contact and to pelvis rotation at elbow extension (r = -0.30 to -0.33). In contrast, in HS athletes, PV was strongly related to EVTA during arm cocking and MER (r = 0.76-0.77). Furthermore, in HS athletes, PV and EVTA during arm cocking and at MER were moderately or strongly related to the other elbow and shoulder torques and forces (r = 0.424-0.991), and EVTA was not related to upper trunk rotation or pelvis rotation throughout the throwing motion (r = -0.16 to 0.15). Conclusion: The kinetic and rotational kinematic differences observed between PRO and HS pitchers in this study may help explain the greater performance of PRO pitchers while allowing them to minimize EVT during pitching. HS pitchers, however, do not appear to be as capable of utilizing the forces generated by rotation of their trunk and pelvis to aid in pitching, and those who throw the hardest generate the greatest forces at the shoulder and elbow. As a result, they experience higher EVTs relative to their body size, which may place them at an increased risk of injury. Clinical Relevance: HS pitchers throw harder primarily by generating larger forces in the arm and shoulder. Thus, owing to the relative physical immaturity of HS versus PRO pitchers, these factors may place them at an increased risk of injury. Coaches may first wish to focus on improving the rotational kinematics of HS pitchers rather than first focusing on achieving greater pitch velocities.

16.
J Neurophysiol ; 119(4): 1556-1561, 2018 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-29357449

RESUMO

There is need for a functional ability test that appropriately assesses the rapid integration of the sensory and motor systems required for older adults to recover from a slip. The purpose of this study was to assess the efficacy and reliability of a novel test, the reactive leg drop, for assessing sensory-motor function in older adults. Fourteen young (YW; mean age = 20 yr) and 11 older women (OW; mean age = 76 yr) participated in this study. For each drop, the leg was passively moved to full extension and then released. The subjects had to recognize their leg was free-falling and reactively kick up as quickly as possible during varying sensory conditions. To assess the leg drop's reliance on proprioception, other proprioceptive tests (e.g., patellar tendon reflexes and balance) were separately performed. Leg drops performed with the eyes closed ( P = 0.011) and with a blocked view of the leg ( P = 0.033) showed significant differences in drop angle between YW and OW. Significant relationships between leg drop conditions and balance were observed in OW that were not present within YW. When collapsed across groups, reflex latency was correlated with drop angle when the eyes were closed. The reactive leg drop was age sensitive, reliable, and likely reliant on proprioception, as shown by relationships to other sensory-motor assessments, such as balance and the patellar reflex. Although more research is needed, we propose that the reactive leg drop is an effective tool to assess sensory-motor integration in a manner that may mimic fall recovery. NEW & NOTEWORTHY The reactive leg drop was age sensitive and was significantly related to other sensory-motor assessments. The ability to accurately assess sensory-motor integration may aid clinicians, practitioners, and researchers in developing new interventions. The reactive leg drop presented in the current study is a potentially effective tool to assess sensory and motor integration in a manner that may mimic fall recovery.


Assuntos
Envelhecimento/fisiologia , Teste de Esforço/normas , Perna (Membro)/fisiologia , Equilíbrio Postural/fisiologia , Propriocepção/fisiologia , Desempenho Psicomotor/fisiologia , Reflexo de Estiramento/fisiologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Reprodutibilidade dos Testes , Adulto Jovem
17.
Int J Exerc Sci ; 9(5): 667-676, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27990227

RESUMO

The use of pre-workout beverages is becoming an increasingly common method of improving performance during exercise in athletic and recreationally active populations. Therefore, the purpose of this study was to investigate the effects of a commercially available energy drink on exercise performance. Thirty-one healthy males (n=23) and females (n=8) participated in this study and were separated into two groups: supplement (SU; n=16) or placebo (PL; n=15). Subjects visited the laboratory on 2 occasions separated by no more than 7 days. The first visit consisted of completing a push up to fatigue protocol (PUFP) without ingesting the pre-workout energy drink supplement (PWEDS). The second visit consisted of ingesting either a placebo or the PWEDS 30 minutes prior to completing the PUFP. Rate of perceived exertion (RPE) was recorded following each set of pushups on both testing days. Also, participant's height, weight, and body composition were collected. There was no significant differences at baseline in any variable between groups (p = >.05). After the second testing session, both groups significantly improved total push-ups (PL Pre: 133.3 ±39.4, PL Post: 155.3 ± 54.1; SU Pre: 139.3 ± 58.5, SU Post: 161.3 ± 79.4; p=<.001), and push-ups completed in each of the 3 sets (p=<.001), when compared to baseline. Post-testing revealed no significant difference between groups in total push-ups completed or RPE at any time point, when compared to baseline. In conclusion, the commercially available PWEDS offered no additional ergogenic effects when compared to the placebo.

18.
Sports (Basel) ; 4(1)2016 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-29910262

RESUMO

The purpose of this study is to provide descriptive and comparative information regarding the cardiorespiratory fitness of professional baseball pitchers. Twenty-four (n = 24) major league (ML) baseball pitchers (starters n = 14; relievers n = 10) over seven seasons (2007⁻2013) were evaluated. A modified Bruce protocol and the CardioCoach™ CO2 metabolic analyzer were used to estimate VO2 max and anaerobic threshold (AT) at the beginning of each season. Performance data from each season was utilized to draw inference about pitching performance. One-way Analysis of Variance (ANOVA) was used to compare Starting (S) and Relief (R) pitchers above/below the group mean for VO2 max and AT. Pearson product moment correlations were also used to examine relationships between cardiorespiratory fitness and performance. Significant differences in performance were discovered between S pitchers above/below the overall group mean for VO2 max. (p ≤ 0.05) and for AT in Walks plus Hits per Inning Pitched (WHIP) (p ≤ 0.05) and Earned Run Average (ERA) (p ≤ 0.05). Significant relationships between VO2 max and Walks per 9 Innings (BB/9) (p ≤ 0.05), Home Runs per 9 innings (HR/9) (p ≤ 0.05), Wins (W) (p ≤ 0.05), Fielding Independent Pitching (FIP) (p ≤ 0.01), Strikeouts (K) (p ≤ 0.01), Hits per 9 innings (H/9) (p ≤ 0.01), Strikeouts per 9 innings (K/9) (p ≤ 0.01), ERA (p ≤ 0.01), and WHIP (p ≤ 0.01). Low, but significant, correlations were discovered between AT and WHIP (p ≤ 0.05) and ERA (≤0.05). CONCLUSION: Higher aerobic capacity appears to be more influential for S than R pitchers. Strength and conditioning practitioners should ensure that pitchers, especially S pitchers at the ML level, perform sufficient and appropriate endurance training to support pitching performance.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...