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2.
Hypertension ; 74(6): 1468-1475, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31607174

RESUMO

We investigated the impact of hypertension on circulatory responses to exercise and the role of the exercise pressor reflex in determining the cardiovascular abnormalities characterizing patients with hypertension. After a 7-day drug washout, 8 hypertensive (mean arterial pressure [MAP] 130±4 mm Hg; 65±3 years) and 8 normotensive (MAP 117±2 mm Hg; 65±2 years) individuals performed single-leg knee-extensor exercise (7 W, 15 W, 50%, 80%-Wpeak) under control conditions and with lumbar intrathecal fentanyl impairing feedback from µ-opioid receptor-sensitive leg muscle afferents. Femoral artery blood flow (QL), MAP (femoral artery), leg vascular conductance, and changes in cardiac output were continuously measured. While the increase in MAP from rest to control exercise was significantly greater in hypertension compared with normotension, the exercise-induced increase in cardiac output was comparable between groups, and QL and leg vascular conductance responses were ≈18% and ≈32% lower in the hypertensive patients (P<0.05). The blockade-induced decreases in MAP were significantly larger during exercise in hypertensive (≈11 mm Hg) compared with normotensive (≈6 mm Hg). Afferent blockade attenuated the central hemodynamic response to exercise similarly in both groups resulting in a ≈15% lower cardiac output at each workload. With no effect in normotensive, afferent blockade significantly raised the peripheral hemodynamic response to exercise in hypertensive, resulting in ≈14% and ≈23% higher QL and leg vascular conductance during exercise. Finally, QL and MAP during fentanyl-exercise in hypertensive were comparable to that of normotensive under control conditions (P>0.2). These findings suggest that exercise pressor reflex abnormalities largely account for the exaggerated MAP response and the impaired peripheral hemodynamics during exercise in hypertension.

3.
Artigo em Inglês | MEDLINE | ID: mdl-31513446

RESUMO

We sought to investigate the role of group III/IV muscle afferents in limiting endurance exercise performance, independently of their role in optimizing locomotor muscle O2 delivery. While breathing 100% O2 to assure a similar arterial O2 content (CaO2) in both trials, 8 male cyclists performed 5-km time trials under control conditions (HCTRL) and with lumbar intrathecal fentanyl (HFENT) impairing neural feedback from the lower limbs. After each time trial, common femoral artery blood flow (FBF) was quantified (Doppler ultrasound) during constant-load cycling, performed at the average power of the preceding time-trial. The assessment of end-tidal gases, hemoglobin content and saturation, and FBF facilitated the calculation of leg O2 delivery. Locomotor muscle activation during cycling was estimated from vastus lateralis EMG. Using electrical femoral nerve stimulation, peripheral and central fatigue were quantified by pre/post-exercise decreases in quadriceps twitch torque (ΔQtw) and voluntary activation (ΔVA), respectively. FBF (~16 ml.min-1.W-1; P=0.6), CaO2 (~24 mlO2.dl-1; P=0.9) and leg O2 delivery (~0.38 mlO2.min-1.W-1; P=0.9) were not different during HCTRL and HFENT. Mean power output and time-to-completion were significantly improved by 9% (~310W vs ~288W) and 3% (~479s vs ~463s), respectively, during HFENT compared to HCTRL. Quadriceps muscle activation was 9±7% higher during HFENT compared to HCTRL (P<0.05). ΔQtw was significantly greater in HFENT compared to HCTRL (54±8% vs 39±9%), while ΔVA was not different (~5%; P=0.3) in both trials. These findings reveal that group III/IV muscle afferent feedback limits whole body endurance exercise performance and peripheral fatigue by restricting neural activation of locomotor muscle.

4.
Environ Int ; 133(Pt A): 105147, 2019 12.
Artigo em Inglês | MEDLINE | ID: mdl-31518932

RESUMO

Exposure to ambient particulate matter is a leading risk factor for environmental public health in India. While Indian authorities implemented several measures to reduce emissions from the power, industry and transportation sectors over the last years, such strategies appear to be insufficient to reduce the ambient fine particulate matter (PM2.5) concentration below the Indian National Ambient Air Quality Standard (NAAQS) of 40 µg/m3 across the country. This study explores pathways towards achieving the NAAQS in India in the context of the dynamics of social and economic development. In addition, to inform action at the subnational levels in India, we estimate the exposure to ambient air pollution in the current legislations and alternative policy scenarios based on simulations with the GAINS integrated assessment model. The analysis reveals that in many of the Indian States emission sources that are outside of their immediate jurisdictions make the dominating contributions to (population-weighted) ambient pollution levels of PM2.5. Consequently, most of the States cannot achieve significant improvements in their air quality and population exposure on their own without emission reductions in the surrounding regions, and any cost-effective strategy requires regionally coordinated approaches. Advanced technical emission control measures could provide NAAQS-compliant air quality for 60% of the Indian population. However, if combined with national sustainable development strategies, an additional 25% population will be provided with clean air, which appears to be a significant co-benefit on air quality (totaling 85%).

5.
J Appl Physiol (1985) ; 126(3): 797, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30907710
6.
Environ Int ; 125: 236-244, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30731373

RESUMO

Air pollution is one of the most harmful consequences of China's rapid economic development and urbanization. Particularly in the Beijing-Tianjin-Hebei (BTH) regions, particulate matter concentrations have consistently exceeded the national air quality standards. Over the last years, China implemented ambitious measures to reduce emissions from the power, industry and transportation sectors, with notable success during the 11th and 12th Five Year Plan (FYP) periods. However, such strategies appear to be insufficient to reduce the ambient PM2.5 concentration below the National Air Quality Standard of 35 µg m-3 across the BTH region within the next 15 years. We find that a comprehensive mitigation strategy for the residential sector in the BTH region would deliver substantial air quality benefits. Beyond the already planned expansion of district heating and natural gas distribution in urban centers and the foreseen curtailment of coal use for households, such a strategy would redirect some natural gas from power generation units towards the residential sector. Rural households would replace biomass for cooking by liquid petroleum gas (LPG) and electricity, and substitute coal for heating by briquettes. Jointly, these measures could reduce the primary PM2.5 and SO2 emissions by 28% and 11%, respectively, and the population-weighted PM2.5 concentrations by 13%, i.e., from 68 µg m-3 to 59 µg m-3. We estimate that such a strategy would reduce premature deaths attributable to ambient and indoor air pollution by almost one third.


Assuntos
Poluição do Ar em Ambientes Fechados/análise , Poluição do Ar , Recuperação e Remediação Ambiental , Habitação , Poluentes Atmosféricos/análise , Poluição do Ar/efeitos adversos , Poluição do Ar/análise , Pequim , China , Carvão Mineral/análise , Culinária , Calefação , Humanos , Mortalidade Prematura , Material Particulado/análise
7.
Artigo em Inglês | MEDLINE | ID: mdl-30587830

RESUMO

Fine particulate matter (PM2.5, diameter ≤2.5 µm) is implicated as the most health-damaging air pollutant. Large cohort studies of chronic exposure to PM2.5 and mortality risk are largely confined to areas with low to moderate ambient PM2.5 concentrations and posit log-linear exposure-response functions. However, levels of PM2.5 in developing countries such as India are typically much higher, causing unknown health effects. Integrated exposure-response functions for high PM2.5 exposures encompassing risk estimates from ambient air, secondhand smoke, and active smoking exposures have been posited. We apply these functions to estimate the future cause-specific mortality risks associated with population-weighted ambient PM2.5 exposures in India in 2030 using Greenhouse Gas-Air Pollution Interactions and Synergies (GAINS) model projections. The loss in statistical life expectancy (SLE) is calculated based on risk estimates and baseline mortality rates. Losses in SLE are aggregated and weighted using national age-adjusted, cause-specific mortality rates. 2030 PM2.5 pollution in India reaches an annual mean of 74 µg/m³, nearly eight times the corresponding World Health Organization air quality guideline. The national average loss in SLE is 32.5 months (95% Confidence Interval (CI): 29.7⁻35.2, regional range: 8.5⁻42.0), compared to an average of 53.7 months (95% CI: 46.3⁻61.1) using methods currently applied in GAINS. Results indicate wide regional variation in health impacts, and these methods may still underestimate the total health burden caused by PM2.5 exposures due to model assumptions on minimum age thresholds of pollution effects and a limited subset of health endpoints analyzed. Application of the revised exposure-response functions suggests that the most polluted areas in India will reap major health benefits only with substantial improvements in air quality.


Assuntos
Poluentes Atmosféricos/efeitos adversos , Exposição Ambiental/estatística & dados numéricos , Modelos Teóricos , Material Particulado/efeitos adversos , Poluentes Atmosféricos/normas , Estudos de Coortes , Exposição Ambiental/efeitos adversos , Exposição Ambiental/normas , Previsões , Humanos , Índia , Expectativa de Vida/tendências , Mortalidade/tendências , Tamanho da Partícula , Material Particulado/normas , Medição de Risco
9.
Prog Brain Res ; 240: 219-246, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30390833

RESUMO

The corticospinal pathway is considered the primary conduit for voluntary motor control in humans. The efficacy of the corticospinal pathway to relay neural signals from higher brain areas to the locomotor muscle, i.e., corticospinal excitability, is subject to alterations during exercise. While the integrity of this motor pathway has historically been examined during single-joint contractions, a small number of investigations have recently focused on whole body exercise, such as cycling or rowing. Although differences in methodologies employed between these studies complicate the interpretation of the existing literature, it appears that the net excitability of the corticospinal pathway remains unaltered during fatiguing whole body exercise. Importantly, this lack of an apparent effect does not designate the absence of change, but a counterbalance of excitatory and inhibitory influences on the two components of the corticospinal pathway, namely the motor cortex and the spinal motoneurons. Specific emphasis is put on group III/IV afferent feedback from locomotor muscle which has been suggested to play a significant role in mediating these changes. Overall, this review aims at summarizing our limited understanding of how fatiguing whole body exercise influences the corticospinal pathway.


Assuntos
Vias Aferentes/fisiologia , Exercício/fisiologia , Fadiga/fisiopatologia , Córtex Motor/fisiologia , Tratos Piramidais/fisiologia , Humanos , Neurônios Motores/fisiologia , Músculo Esquelético/inervação
10.
J Physiol ; 596(19): 4789-4801, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-30095164

RESUMO

KEY POINTS: This study investigated the influence of group III/IV muscle afferents on corticospinal excitability during cycling exercise and focused on GABAB neuron-mediated inhibition as a potential underlying mechanism. The study provides novel evidence to demonstrate that group III/IV muscle afferent feedback facilitates inhibitory intracortical neurons during whole body exercise. Firing of these interneurons probably contributes to the development of central fatigue during physical activity. ABSTRACT: We investigated the influence of group III/IV muscle afferents in determining corticospinal excitability during cycling exercise and focused on GABAB neuron-mediated inhibition as a potential underlying mechanism. Both under control conditions (CTRL) and with lumbar intrathecal fentanyl (FENT) impairing feedback from group III/IV leg muscle afferents, subjects (n = 11) cycled at a comparable vastus-lateralis EMG signal (∼0.26 mV) before (PRE; 100 W) and immediately after (POST; 90 ± 2 W) fatiguing constant-load cycling exercise (80% Wpeak; 221 ± 10 W; ∼8 min). During, PRE and POST cycling, single and paired-pulse (100 ms interstimulus interval) transcranial magnetic stimulations (TMS) were applied to elicit unconditioned and conditioned motor-evoked potentials (MEPs), respectively. To distinguish between cortical and spinal contributions to the MEPs, cervicomedullary stimulations (CMS) were used to elicit unconditioned (CMS only) and conditioned (TMS+CMS, 100 ms interval) cervicomedullary motor-evoked potentials (CMEPs). While unconditioned MEPs were unchanged from PRE to POST in CTRL, unconditioned CMEPs increased significantly, resulting in a decrease in unconditioned MEP/CMEP (P < 0.05). This paralleled a reduction in conditioned MEP (P < 0.05) and no change in conditioned CMEP. During FENT, unconditioned and conditioned MEPs and CMEPs were similar and comparable during PRE and POST (P > 0.2). These findings reveal that feedback from group III/IV muscle afferents innervating locomotor muscle decreases the excitability of the motor cortex during fatiguing cycling exercise. This impairment is, at least in part, determined by the facilitating effect of these sensory neurons on inhibitory GABAB intracortical interneurons.


Assuntos
Potencial Evocado Motor/fisiologia , Exercício , Córtex Motor/fisiologia , Fadiga Muscular , Células Receptoras Sensoriais/fisiologia , Adulto , Vias Aferentes/fisiologia , Ciclismo , Feminino , Humanos , Masculino , Contração Muscular , Vias Neurais/fisiologia , Estimulação Magnética Transcraniana
11.
Med Sci Sports Exerc ; 50(12): 2409-2417, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30102675

RESUMO

PURPOSE: The effect of an acute bout of exercise, especially high-intensity exercise, on the function of mitochondrial respiratory complexes is not well understood, with potential implications for both the healthy population and patients undergoing exercise-based rehabilitation. Therefore, this study sought to comprehensively examine respiratory flux through the different complexes of the electron transport chain in skeletal muscle mitochondria before and immediately after high-intensity aerobic exercise. METHODS: Muscle biopsies of the vastus lateralis were obtained at baseline and immediately after a 5-km time trial performed on a cycle ergometer. Mitochondrial respiratory flux through the complexes of the electron transport chain was measured in permeabilized skeletal muscle fibers by high-resolution respirometry. RESULTS: Complex I + II state 3 (state 3CI + CII) respiration, a measure of oxidative phosphorylation capacity, was diminished immediately after the exercise (pre, 27 ± 3 ρm·mg·s; post, 17 ± 2 ρm·mg·s; P < 0.05). This decreased oxidative phosphorylation capacity was predominantly the consequence of attenuated complex II-driven state 3 (state 3CII) respiration (pre, 17 ± 1 ρm·mg·s; post, 9 ± 2 ρm·mg·s; P < 0.05). Although complex I-driven state 3 (3CI) respiration was also lower (pre, 20 ± 2 ρm·mg·s; post, 14 ± 4 ρm·mg·s), this did not reach statistical significance (P = 0.27). In contrast, citrate synthase activity, proton leak (state 2 respiration), and complex IV capacity were not significantly altered immediately after the exercise. CONCLUSIONS: These findings reveal that acute high-intensity aerobic exercise significantly inhibits skeletal muscle state 3CII and oxidative phosphorylation capacity. This, likely transient, mitochondrial defect might amplify the exercise-induced development of fatigue and play an important role in initiating exercise-induced mitochondrial adaptations.


Assuntos
Transporte de Elétrons , Exercício , Mitocôndrias Musculares/fisiologia , Fibras Musculares Esqueléticas/fisiologia , Músculo Quadríceps/fisiologia , Adulto , Biópsia , Respiração Celular , Humanos , Masculino , Fosforilação Oxidativa , Consumo de Oxigênio
12.
Am J Physiol Regul Integr Comp Physiol ; 315(4): R741-R750, 2018 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-29995457

RESUMO

To examine the impact of aging on neuromuscular fatigue following cycling (CYC; large active muscle mass) and single-leg knee-extension (KE; small active muscle mass) exercise, 8 young (25 ± 4 years) and older (72 ± 6 years) participants performed CYC and KE to task failure at a given relative intensity (80% of peak power output). The young also matched CYC and KE workload and duration of the old (iso-work comparison). Peripheral and central fatigue were quantified via pre-/postexercise decreases in quadriceps twitch torque (∆Qtw, electrical femoral nerve stimulation) and voluntary activation (∆VA). Although young performed 77% and 33% more work during CYC and KE, respectively, time to task failure in both modalities was similar to the old (~9.5 min; P > 0.2). The resulting ΔQtw was also similar between groups (CYC ~40%, KE ~55%; P > 0.3); however, ∆VA was, in both modalities, approximately double in the young (CYC ~6%, KE ~9%; P < 0.05). While causing substantial peripheral and central fatigue in both exercise modalities in the old, ∆Qtw in the iso-work comparison was not significant (CYC; P = 0.2), or ~50% lower (KE; P < 0.05) in the young, with no central fatigue in either modality ( P > 0.4). Based on iso-work comparisons, healthy aging impairs fatigue resistance during aerobic exercise. Furthermore, comparisons of fatigue following exercise at a given relative intensity mask the age-related difference observed following exercise performed at the same workload. Finally, although active muscle mass has little influence on the age-related difference in the rate of fatigue at a given relative intensity, it substantially impacts the comparison during exercise at a given absolute intensity.


Assuntos
Exercício , Nervo Femoral/fisiologia , Contração Muscular , Fadiga Muscular , Força Muscular , Tratos Piramidais/fisiologia , Músculo Quadríceps/inervação , Adulto , Fatores Etários , Idoso , Ciclismo , Estimulação Elétrica/métodos , Eletromiografia , Potencial Evocado Motor , Humanos , Masculino , Tempo de Reação , Fatores de Tempo , Torque , Estimulação Magnética Transcraniana , Adulto Jovem
14.
Exp Gerontol ; 111: 154-161, 2018 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-30031838

RESUMO

Aging is associated with a progressive decline in skeletal muscle function, then leading to impaired exercise tolerance. Maximal strength training (MST) appears to be a practical and effective intervention to increase both exercise capacity and efficiency. However, the underlying physiological mechanisms responsible for these functional improvements are still unclear. Accordingly, the purpose of this study was to examine the intramuscular and metabolic adaptations induced by 8 weeks of knee-extension MST in the quadriceps of 10 older individuals (75 ±â€¯9 yrs) by employing a combination of molecular, magnetic resonance 1H-imaging and 31P-spectroscopy, muscle biopsies, motor nerve stimulation, and indirect calorimetry techniques. Dynamic and isometric muscle strength were both significantly increased by MST. The greater torque-time integral during sustained isometric maximal contraction post-MST (P = 0.002) was associated with increased rates of ATP synthesis from anaerobic glycolysis (PRE: 10 ±â€¯7 mM·min-1; POST: 14 ±â€¯7 mM·min-1, P = 0.02) and creatine kinase reaction (PRE: 31 ±â€¯10 mM·min-1; POST: 41 ±â€¯10 mM·min-1, P = 0.006) such that the ATP cost of contraction was not significantly altered. Expression of fast myosin heavy chain, quadriceps muscle volume, and submaximal cycling net efficiency were also increased with MST (P = 0.005; P = 0.03 and P = 0.03, respectively). Overall, MST induced a shift toward a more glycolytic muscle phenotype allowing for greater muscle force production during sustained maximal contraction. Consequently, some of the MST-induced improvements in exercise tolerance might stem from a greater anaerobic capacity to generate ATP, while the improvement in exercise efficiency appears to be independent from an alteration in the ATP cost of contraction.


Assuntos
Trifosfato de Adenosina/metabolismo , Envelhecimento/fisiologia , Exercício , Contração Isométrica , Músculo Quadríceps/fisiologia , Adaptação Fisiológica , Idoso , Idoso de 80 Anos ou mais , Metabolismo Energético , Tolerância ao Exercício , Feminino , Glicólise , Humanos , Joelho/fisiologia , Masculino , Força Muscular , Fatores de Tempo
15.
J Physiol ; 596(12): 2301-2314, 2018 06.
Artigo em Inglês | MEDLINE | ID: mdl-29644702

RESUMO

KEY POINTS: This investigation assessed the influence of group III/IV muscle afferents on small muscle mass exercise performance from a skeletal muscle bioenergetics perspective. Group III/IV muscle afferent feedback was attenuated with lumbar intrathecal fentanyl during intermittent isometric single-leg knee-extensor all-out exercise, while 31 P-MRS was used to assess skeletal muscle bioenergetics. Attenuation of group III/IV muscle afferent feedback improved exercise performance during the first minute of exercise, due to an increase in total ATP production with no change in the ATP cost of contraction. However, exercise performance was not altered during the remainder of the protocol, despite a sustained increase in total ATP production, due to an exacerbated ATP cost of contraction. These findings reveal that group III/IV muscle afferents directly limit exercise performance during small muscle mass exercise, but, due to their critical role in maintaining skeletal muscle contractile efficiency, with time, the benefit of attenuating the muscle afferents is negated. ABSTRACT: The direct influence of group III/IV muscle afferents on exercise performance remains equivocal. Therefore, all-out intermittent isometric single-leg knee-extensor exercise and phosphorous magnetic resonance spectroscopy (31 P-MRS) were utilized to provide a high time resolution assessment of exercise performance and skeletal muscle bioenergetics in control conditions (CTRL) and with the attenuation of group III/IV muscle afferent feedback via lumbar intrathecal fentanyl (FENT). In both conditions, seven recreationally active men performed 60 maximal voluntary quadriceps contractions (MVC; 3 s contraction, 2 s relaxation), while knee-extensor force and 31 P-MRS were assessed during each MVC. The cumulative integrated force was significantly greater (8 ± 6%) in FENT than CTRL for the first minute of the all-out protocol, but was not significantly different for the second to fifth minutes. Total ATP production was significantly greater (16 ± 21%) in FENT than CTRL throughout the all-out exercise protocol, due to a significantly greater anaerobic ATP production (11 ± 13%) in FENT than CTRL with no significant difference in oxidative ATP production. The ATP cost of contraction was not significantly different between FENT and CTRL for the first minute of the all-out protocol, but was significantly greater (29 ± 34%) in FENT than in CTRL for the second to fifth minutes. These findings reveal that group III/IV muscle afferents directly limit exercise performance during small muscle mass exercise, but, due to their critical role in maintaining skeletal muscle contractile efficiency, with time, the benefit from muscle afferent attenuation is negated.


Assuntos
Vias Aferentes/fisiologia , Metabolismo Energético , Exercício , Contração Muscular , Músculo Esquelético/inervação , Músculo Esquelético/fisiologia , Trifosfato de Adenosina/metabolismo , Adulto , Analgésicos Opioides/administração & dosagem , Fentanila/administração & dosagem , Humanos , Masculino , Músculo Esquelético/efeitos dos fármacos
16.
J Physiol ; 596(8): 1373-1384, 2018 04 15.
Artigo em Inglês | MEDLINE | ID: mdl-29388218

RESUMO

KEY POINTS: We investigated the contribution of group III/IV muscle afferents to carotid baroreflex resetting during electrically evoked (no central command) and voluntary (requiring central command) isometric knee extension exercise. Lumbar intrathecal fentanyl was used to attenuate the central projection of µ-opioid receptor-sensitive group III/IV leg muscle afferent feedback. Spontaneous carotid baroreflex control was assessed by loading and unloading the carotid baroreceptors with a variable pressure neck chamber. Group III/IV muscle afferents did not influence spontaneous carotid baroreflex responsiveness at rest or during exercise. Afferent feedback accounted for at least 50% of the exercise-induced increase in the carotid baroreflex blood pressure and heart rate operating points, adjustments that are critical for an appropriate cardiovascular response to exercise. These findings suggest that group III/IV muscle afferent feedback is, independent of central command, critical for the resetting of the carotid baroreflex blood pressure and heart rate operating points, but not for spontaneous baroreflex responsiveness. ABSTRACT: This study sought to comprehensively investigate the role of metabolically and mechanically sensitive group III/IV muscle afferents in carotid baroreflex responsiveness and resetting during both electrically evoked (EVO, no central command) and voluntary (VOL, requiring central command) isometric single-leg knee-extension (15% of maximal voluntary contraction; MVC) exercise. Participants (n = 8) were studied under control conditions (CTRL) and following lumbar intrathecal fentanyl injection (FENT) to inhibit µ-opioid receptor-sensitive lower limb muscle afferents. Spontaneous carotid baroreflex control of mean arterial pressure (MAP) and heart rate (HR) were assessed following rapid 5 s pulses of neck pressure (NP, +40 mmHg) or suction (NS, -60 mmHg). Resting MAP (87 ± 10 mmHg) and HR (70 ± 8 bpm) were similar between CTRL and FENT conditions (P > 0.4). In terms of spontaneous carotid baroreflex responsiveness, FENT did not alter the change in MAP or HR responses to NP (+13 ± 5 mmHg, P = 0.85; +9 ± 3 bpm; P = 0.99) or NS (-13 ± 5 mmHg, P = 0.99; -24 ± 11 bpm; P = 0.49) at rest or during either exercise protocol, which were of a remarkably similar magnitude to rest. In contrast, FENT administration reduced the exercise-induced resetting of the operating point for MAP and HR during both EVO (116 ± 10 mmHg to 100 ± 15 mmHg and 93 ± 14 bpm to 82 ± 10 bpm) and VOL (107 ± 13 mmHg to 100 ± 17 mmHg and 89 ± 10 bpm to 72 ± 10 bpm) exercise bouts. Together, these findings document that group III/IV muscle afferent feedback is critical for the resetting of the carotid baroreflex MAP and HR operating points, independent of exercise-induced changes in central command, but not for spontaneous carotid baroreflex responsiveness.


Assuntos
Barorreflexo , Pressão Sanguínea , Corpo Carotídeo/fisiologia , Exercício , Frequência Cardíaca , Neurônios Motores/fisiologia , Músculo Esquelético/fisiologia , Adulto , Humanos , Masculino , Músculo Esquelético/inervação
17.
Med Sci Sports Exerc ; 50(4): 809-816, 2018 04.
Artigo em Inglês | MEDLINE | ID: mdl-29117071

RESUMO

PURPOSE: To investigate the effects of feedback, in the form of a virtual avatar paced at 100% and 102% of baseline performance, on neuromuscular fatigue after a 4-km cycling time trial (TT). We hypothesized that improved cycling performance would occur because of the participants exceeding a previously established critical threshold and experiencing greater neuromuscular fatigue. METHODS: After familiarization, 10 well-trained cyclists performed a baseline 4-km TT without feedback (BASE), followed by two 4-km TT where they raced against an avatar (set at 100% accurate [ACC] and 102% deception [DEC] of baseline power output) in a randomized and counterbalanced order. Before and after each TT, neuromuscular fatigue was assessed using maximal isometric voluntary contractions (MVC) of the quadriceps, and supramaximal electrical stimulation of the femoral nerve, during and 2 s after MVCs to assess voluntary activation and potentiated twitch force. Blood lactate was taken pretrials and posttrials and RPE was taken throughout each TT. RESULTS: Time trial performance improved after deception of feedback compared with baseline performance (-5.8 s, P = 0.019). Blood lactate increased after DEC compared with BASE (+1.37 mmol·L, P = 0.019). Despite this, there was no difference in any measures of exercise-induced neuromuscular fatigue (P > 0.05). Similarly, RPE was not different between trials. CONCLUSIONS: Well-trained male cyclists can improve cycling TT performance when competing against an avatar increased to 102% of a previously established best effort. However, this improvement is not associated with a measurable augmentation of neuromuscular fatigue.


Assuntos
Desempenho Atlético/psicologia , Ciclismo/psicologia , Decepção , Fadiga Muscular , Adulto , Estimulação Elétrica , Humanos , Contração Isométrica , Ácido Láctico/sangue , Masculino , Músculo Quadríceps/fisiologia , Adulto Jovem
18.
Am J Physiol Heart Circ Physiol ; 314(3): H464-H474, 2018 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-29167119

RESUMO

Heart failure (HF) is a global public health problem that, independent of its etiology [reduced (HFrEF) or preserved ejection fraction (HFpEF)], is characterized by functional impairments of cardiac function, chemoreflex hypersensitivity, baroreflex sensitivity (BRS) impairment, and abnormal autonomic regulation, all of which contribute to increased morbidity and mortality. Exercise training (ExT) has been identified as a nonpharmacological therapy capable of restoring normal autonomic function and improving survival in patients with HFrEF. Improvements in autonomic function after ExT are correlated with restoration of normal peripheral chemoreflex sensitivity and BRS in HFrEF. To date, few studies have addressed the effects of ExT on chemoreflex control, BRS, and cardiac autonomic control in HFpEF; however, there are some studies that have suggested that ExT has a beneficial effect on cardiac autonomic control. The beneficial effects of ExT on cardiac function and autonomic control in HF may have important implications for functional capacity in addition to their obvious importance to survival. Recent studies have suggested that the peripheral chemoreflex may also play an important role in attenuating exercise intolerance in HFrEF patients. The role of the central/peripheral chemoreflex, if any, in mediating exercise intolerance in HFpEF has not been investigated. The present review focuses on recent studies that address primary pathophysiological mechanisms of HF (HFrEF and HFpEF) and the potential avenues by which ExT exerts its beneficial effects.


Assuntos
Sistema Nervoso Autônomo/fisiopatologia , Células Quimiorreceptoras/metabolismo , Terapia por Exercício/métodos , Tolerância ao Exercício , Insuficiência Cardíaca/terapia , Coração/inervação , Músculo Esquelético/inervação , Reflexo , Volume Sistólico , Animais , Metabolismo Energético , Insuficiência Cardíaca/diagnóstico , Insuficiência Cardíaca/metabolismo , Insuficiência Cardíaca/fisiopatologia , Humanos , Contração Muscular , Músculo Esquelético/metabolismo , Recuperação de Função Fisiológica , Resultado do Tratamento
19.
Eur J Sport Sci ; 18(1): 13-24, 2018 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-27821022

RESUMO

Neuromuscular fatigue compromises exercise performance and is determined by central and peripheral mechanisms. Interactions between the two components of fatigue can occur via neural pathways, including feedback and feedforward processes. This brief review discusses the influence of feedback and feedforward mechanisms on exercise limitation. In terms of feedback mechanisms, particular attention is given to group III/IV sensory neurons which link limb muscle with the central nervous system. Central corollary discharge, a copy of the neural drive from the brain to the working muscles, provides a signal from the motor system to sensory systems and is considered a feedforward mechanism that might influence fatigue and consequently exercise performance. We highlight findings from studies supporting the existence of a 'critical threshold of peripheral fatigue', a previously proposed hypothesis based on the idea that a negative feedback loop operates to protect the exercising limb muscle from severe threats to homeostasis during whole-body exercise. While the threshold theory remains to be disproven within a given task, it is not generalisable across different exercise modalities. The 'sensory tolerance limit', a more theoretical concept, may address this issue and explain exercise tolerance in more global terms and across exercise modalities. The 'sensory tolerance limit' can be viewed as a negative feedback loop which accounts for the sum of all feedback (locomotor muscles, respiratory muscles, organs, and muscles not directly involved in exercise) and feedforward signals processed within the central nervous system with the purpose of regulating the intensity of exercise to ensure that voluntary activity remains tolerable.


Assuntos
Exercício/fisiologia , Fadiga , Retroalimentação Fisiológica , Resistência Física/fisiologia , Humanos , Neurônios Aferentes/fisiologia
20.
Lancet ; 391(10120): 581-630, 2018 02 10.
Artigo em Inglês | MEDLINE | ID: mdl-29096948
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