We investigated central fatigue during maximal exercise (EXmax) after 12×20-min respiratory muscle endurance training (eRMT) sessions over 4 weeks using cerebral near-infrared spectroscopy (NIRS; left, right prefrontal cortices: LPFC, RPFC); and self-reported effort perceptions (RPE). Healthy participants improved eRMT performance with no spirometry changes. Pre-eRMT, EXmax oxygenated (O2Hb), deoxygenated (HHb), and total (tHb) hemoglobin increases were larger in LPFC than RPFC. Post-eRMT, EXmax O2Hb, HHb, and tHb increases were smaller in LPFC than RPFC. Post-eRMT EXmax RPE were smaller. eRMT-induced LPFC-to-RPFC hemodynamic shifts during EXmax may facilitate decreased RPE.
This study investigated the influence of moderate-intensity exercise (EX; 20 min cycling exercise, 60% heart rate reserve) on executive function (EF) and prefrontal cortex (PFC) hemodynamics, compared to control (CON; 20 min seated, listening to statistics audio recording). EF tests were Go/NoGo, Task Switching, and Reading Span. Near-infrared spectroscopy (NIRS) measured total hemoglobin concentration (tHb). Compared to CON, right PFC tHb was elevated from baseline at 0 and 15 min post-EX during Go/NoGO and Task Switching, and at 0 min post-EX during Reading Span. In both EX and CON, tHb was unchanged during “rest” between EF tests.
Our goal was to use 2-channel frequency domain near-infrared spectroscopy (NIRS) to investigate the hemodynamic and metabolic mechanisms underlying hyperglycemia-associated long-term memory impairment. We hypothesized that prefrontal cortex (PFC) oxygen saturation (%Sat) and perfusion (tHb, i.e. total hemoglobin) would decrease due to hyperglycemia during learning, and then increase during recall. During learning, participants’ blood glucose was manipulated with beverages containing either 47.4 mg saccharine control (CON, n = 10), or 50 g dextrose + 23.7 mg saccharine (GLC, n = 10). In the Symbol-Digit Modalities Test (SMDT) participants matched nine symbols to corresponding digits (1-9 inclusive), completing 105 learning and 15 testing trials on day 1 and 15 testing trials on day 2. From learning to recall, CON SMDT performance was unchanged, but GLC SMDT performance was decreased 11% (P = 0.0173). There were significant interactions (2-way ANOVA) between the CON-GLC treatment effects and the learning-recall effects for both PFC perfusion and oxygen saturation. Specifically, comparing learning to recall, CON exhibited no tHb differences but for GLC there was a large tHb decrease during learning with a partial recovery toward CON values during recall (P = 0.0012); and, comparing learning to recall, CON exhibited a large %Sat decrease but GLC exhibited a large %Sat increase (P = 0.021). We speculate that, during learning, after overnight fasting (CON) the PFC demands more hemodynamic and metabolic resources and “works” harder, but with readily available sugar (GLC) the PFC exhibits decreased “effort.”
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