Role of carbohydrate in central fatigue: a systematic review

Abstract

Carbohydrate (CHO) depletion is linked to neuromuscular fatigue during exercise. While its role at peripheral level is relatively well understood, less is known about its impact centrally. The aim of this systematic review was to critically analyze the effects of CHO on central fatigue (CF) assessed by various neurophysiological techniques. Four databases were searched using PRISMA guidelines through February 2016. The inclusion criteria were: CHO as intervention against a placebo control, fatigue induced by prolonged exercise and assessed using neurophysiological measures [voluntary activation (VA), superimposed twitch (SIT), M-wave, electromyography], alongside maximal voluntary contraction (MVC). Seven papers were reviewed, where exercise duration lasted between 115 and 180 min. CHO improved exercise performance in three studies, whereby two of them attributed it to CF via attenuation of VA and SIT reductions, while the other indicated peripheral involvement via attenuation of M-wave reduction. Although a few studies suggest that CHO attenuates CF, data on its direct effects on neurophysiological outcome measures are limited and mixed. Generally, measures employed in these studies were inadequate to conclude central contribution to fatigue. Factors including the techniques used and the lack of controls render additional confounding factors to make definitive deductions. Future studies should employ consistent techniques and appropriate neurophysiological controls to distinguish CHO effect at central level. The use of pharmacological intervention should be incorporated to elucidate involvement of central mechanisms.

Effects of a commercially available branched-chain amino acid-alanine-carbohydrate-based sports supplement on perceived exertion and performance in high intensity endurance cycling tests

“…In particular, BCAA were shown to positively impact the rating of perceived exertion (RPE) [14] and performance [21,22]. However, due to the great heterogeneity of the experimental protocols and formulations used, the results of these studies are not always unequivocal; hence, the actual efficacy of BCAAused alone or combined with other components -remains a much debated issue [15,23,24].…”

Enjuagues bucales con carbohidratos y su efecto en el rendimiento de carreras contrarreloj: Revisión sistemática

“…Actualmente, se sabe que el rendimiento deportivo está regulado por la disponibilidad de sustratos energéticos, ante la falta de CHO el sistema nervioso recibe señales que dan cuenta de una disminución generalizada de su utilización a nivel celular; la célula pasa de consumir Adenosin-trifosfato (ATP) a producir ATP, induciendo el desarrollo fatiga muscular y la inhibición de síntesis proteica (3)(4)(5)(6) . La literatura recomienda un consumo cercano al 50 a 60% de la ingesta calórica total para población normal, no obstante, estas recomendaciones no son muy específicas en deportistas puesto que generalmente no especifican variables como el tipo de actividad y el nivel del deportista (4,(7)(8)(9) .…”

Effect of quantity and quality of pre-exercise carbohydrate meals on central fatigue

“…While time to exhaustion could indicate fatigue during endurance exercise, CF is typically observed through the drop-in force-generating capacity (i.e., MVC) alongside other neurophysiological measurements, such as VA, where a reduction indicates lowered neural drive which could originate from spinal and/or supraspinal sites. In our recent review, we summarized that most studies that investigated the effect of CHO on CF did not employ standard neurophysiological techniques to distinguish the peripheral and central involvement of CHO in fatigue (23). Nybo (28) showed that hypoglycemia reduces CAR, whereas CHO supplementation during exercise preserves it.…”

“…Pre-exercise consumption of CHO-rich meals has been shown to produced mixed results with respect to time to exhaustion, as discussed in a review by Ormsbee (30); furthermore, only two studies listed by the authors compared the effect of high-versus low-CHO meals. More importantly, to date, there is no study, to our knowledge, that has compared the effects of high and low pre-exercise CHO meals on CF using neurophysiological measures (23). It should be noted that it is difficult and of ethical concern to measure serotonin from cerebrospinal fluid during exercise.…”