Traditional Models of Fatigue and Physical Performance

Abstract

The origin of fatigue has been the focus of studies involved in sports performance, due to the necessity to clarify the mechanistic bases for the reduced capacity to perform considerable effort intensities. According to the traditional conception of fatigue, mechanisms may encompass peripheral and central sites of fatigue. Peripheral fatigue is understood as events related to an inefficient tissue oxygen delivery, metabolic accumulation, muscular acidosis and muscle substrate depletion. In contrast, the central fatigue is mostly related to events in the central nervous system (CNS) that may involve neurotransmitters changes, altered metabolic profile and elevated temperature. Therefore, the current review aimed to discuss the peripheral and central mechanisms of fatigue, thus driving interpretations of the phenomenon. Palavras-chave: Oxygen. Muscle glycogen. Exercise limitation. RESUMO A etiologia da fadiga tem sido objeto de estudo em pesquisas relacionadas ao desempenho esportivo em função da necessidade de esclarecer os mecanismos que reduzem a capacidade de manutenção do desempenho em intensidades elevadas de esforço. A concepção tradicional de fadiga assume que os mecanismos possam ser desencadeados em sítios de ação central ou periférica. A fadiga periférica é compreendida como uma oferta inadequada de oxigênio tecidual, acúmulo de metabólitos e depleção de substrato energético acelerando a acidose muscular. A fadiga central, por sua vez, oriunda do sistema nervoso central (SNC), apresenta alterações nos neurotransmissores, podendo alterar o perfil metabólico e temperatura do SNC. Desta forma, a presente revisão tem como intuito abordar os mecanismos de fadiga central e periférica, norteando futuras interpretações sobre o fenômeno. Palavras-chave: Oxigênio. Glicogênio muscular. Limitação do exercício.

Caffeine Increased Muscle Endurance Performance Despite Reduced Cortical Activation and Unchanged Neuromuscular Efficiency and Corticomuscular Coherence

“…Such an ineffectiveness of caffeine in improving peripheral responses may be related to the muscle contraction stimulation frequency of the submaximal IC exercise, as it has been proposed that caffeine changes muscle properties through alterations in calcium release rather than through potassium accumulation [33]. Thus, assuming that calcium metabolism is associated with force losses mainly in frequencies <20–30 Hz [7,34,35] and that our submaximal IC exercise required a muscle contraction frequency mostly higher than 50 Hz [36], perhaps caffeine ingestion is ineffective in improving key muscular properties enhance muscle endurance performance during submaximal IC. Somehow, the fact that coherence analysis indicated a significant coupling between gamma wave EEG (30–50 Hz) and EMG may reinforce this argument.…”

Exploring the Mediating Role of Sleep Deficit-Related Functional Status in Subacute Stroke Survivors

“…Each question is rated on a 5-point Likert scale (0 = no problem; 4 = very severe problem), resulting in a total score that ranges from 0 to 28. The following categories of insomnia were used to interpret the overall score: severe insomnia (22)(23)(24)(25)(26)(27)(28), moderate insomnia (15)(16)(17)(18)(19)(20)(21), sub-threshold insomnia (8)(9)(10)(11)(12)(13)(14), and no insomnia (0-7) [28]. The validity of the ISI has been established in various populations using robust methodologies, including Southeast Asians [30][31][32].…”

“…The various reasons suggested for post-stroke fatigue include increased tissue inflammation [ 9 ], alterations in excitability, and disruptions in the connections between various brain areas due to stroke pathology [ 10 ]. Central models of fatigue attribute this condition to changes in the functioning of the CNS [ 11 ]. The reported prevalence of PSF is around 50%, and it may improve or worsen over time [ 12 , 13 ].…”

A Narrative Review of Current Concerns and Future Perspectives of the Carbohydrate Mouth Rinse Effects on Exercise Performance

“…A greater peripheral fatigue was detected as the shorter cycling time trial progressed (i.e., 4 km cycling time trial), in contrast to the greater central fatigue found after longer cycling time trials such as 20 km and 40 km. 20 The hypothesis was that participants completing the 4 km cycling trial faced higher levels of muscle metabolites-induced neuromuscular fatigue (47) such as hydrogen and potassium accumulation, 54 , 55 thus contrasting to centrally mediated reductions in motor command and voluntary activation in 40 km cycling time trial. 56 Somehow, this different exercise intensity-neuromuscular fatigue interplay may provide rationale to the controversial results involving endurance exercise protocols, as addressed below.…”