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INTRODUCTION: The tolerable duration (t) for high-intensity cycle ergometry bears a hyperbolic relationship to the power output (P) with an asymptote termed the critical power (CP), and a curvature constant (W') that is numerically equivalent to an amount of work that can be performed above CP. The physiological nature of W' has received little consideration compared with CP, e.g., whether the total amount of work above CP remains constant when the power actually changes during the high-intensity task. PURPOSE: The purpose of this study was to compare W' derived from the standard estimation method, consisting of several different constant-P tests, and the total amount of work above CP during an exhausting exercise bout using a variable-P protocol. METHODS: Eleven healthy male subjects (age: 21-40 yr) volunteered to participate in this study. Each initially performed four-to-six high-intensity square-wave exercise bouts for estimation of CP [mean (SD); 213.3 (22.4) W] and W' [12.68 (3.08) kJ]. The subjects subsequently performed two variable-P tests to the limit of tolerance. During the first part, P was 117% or 134% of CP for a duration that expended approximately half of W'. The work rate was then abruptly increased to 134% (UP protocol) or decreased to 117% (DOWN protocol) of CP for the second part. RESULTS: There were no significant differences between W' [12.68 (3.08) kJ] and the total amount of work above CP during the UP [12.14 (4.18) kJ] and DOWN [12.72 (4.05) kJ] protocols (P > 0.05). CONCLUSION: We conclude that the work equivalent of W' is not affected by power variations during exhausting cycle ergometry, at least in the P range of 100-134% of CP. [ABSTRACT FROM AUTHOR]

Breakfast skipping has been suggested to be associated with cardiovascular diseases. However, whether breakfast skipping affects vascular endothelial function (VEF), a marker of cardiovascular diseases, remains unclear. This study aimed to investigate the impact of breakfast consumption (Eating trial) and skipping (Skipping trial) on brachial artery (BA) VEF in healthy breakfast eaters. A total of nine healthy individuals (4 females and 5 males) either had breakfast between 830 and 900 or skipped it and had lunch between 1200 and 1230, followed by a 3-h rest period until 1530. For BA VEF evaluation, flow-mediated dilation (FMD) was measured by ultrasound before and after breakfast and lunch. FMD was calculated as the percent change in BA diameter normalized to the shear rate area under the curve (FMD/SR AUC ). Blood glucose, plasma insulin, and plasma free fatty acid levels in capillaries were measured before and after breakfast and lunch. At 1530, the Eating trial, but not the Skipping trial, significantly increased FMD/SR AUC from baseline ( P = 0.006). The Skipping trial showed significantly lower changes in FMD/SR AUC from 830 than the Eating trial at 1530 ( P < 0.001). We found a significant inverse correlation between changes in FMD/SR AUC between 830 and 1530 and peak glucose levels after lunch ( r = -0.882, P < 0.001) and with an incremental area under the curve for glucose between 830 and 1530 ( r = -0.668, P < 0.001). These results suggest that a single bout of breakfast skipping can suppress BA VEF in the afternoon because of postlunch hyperglycemia. NEW & NOTEWORTHY Skipping breakfast does not affect vascular endothelial function (VEF) before lunch. However, after lunch on normal meals (i.e., not oral glucose tolerance test), VEF was found to be lower in those who skipped breakfast than those who ate breakfast. Such reduced postlunch VEF after skipping breakfast was associated with postprandial hyperglycemia. These results provide important insight into the impact of eating breakfast on VEF and glycemic control in healthy adults.

Postprandial regulation of the gastric emptying (GE) rate plays an important role in food intake. Although oral sweetening with glucose may accelerate GE, the effects of different sweetness intensities of glucose (10% and 20%, w/v) and other energy sweeteners (e.g. fructose and sucrose) remain uncertain. The purpose of this study was to determine the effects of different glucose concentrations (Experiment 1) and different sugars with the same sweet taste intensity (Experiment 2) on postprandial GE. In both experiments, after ingesting a 200 kcal carbohydrate solution containing 50 g of maltodextrin, participants repeatedly sipped, but did not swallow, one of three (water, 10% and 20%, w/v glucose) or four (water and equally sweet 20%, w/v glucose, 12%, w/v fructose, and 14%, w/v sucrose) solutions for 1 min every 5 min over a 30 min period. GE was evaluated by measuring the temporal change in the cross-sectional area of the gastric antrum using ultrasound. In Experiment 1, oral stimulation with 20% (w/v) glucose resulted in greater GE than the control stimulus (i.e. water), but the effect of stimulation with 10% (w/v) glucose on GE was not different from that of the control stimulus. In Experiment 2, stimulation with 20% (w/v) glucose or 12% (w/v) fructose resulted in greater GE than the control stimulus. However, the effect of stimulation with 14% (w/v) sucrose on GE did not differ from that of the control stimulus. Consequently, oral stimulation with glucose or fructose solutions of moderate to high sweetness following a meal facilitates postprandial GE., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Blood glucose levels acutely increase postprandially depending on the type of meal consumed. However, it remains unclear whether postprandial hyperglycemia temporally affects cardiovascular responses to static handgrip exercise (SHG-ex). Thus, this study aimed to examine whether increased blood glucose induced by consumption of a high-glycemic index (HGI) meal affects pressor response to SHG-ex. A total of 14 healthy participants (7 women and 7 men) consumed an HGI meal, a low-glycemic index (LGI) meal, or no meal (control). Participants performed 30% maximal voluntary contraction SHG-ex followed by a postexercise muscle ischemia (PEMI) test before the meal and 60 min after consuming the meal. Blood glucose, plasma insulin, and plasma triglyceride levels were measured, and the area under the curve until 60 min (AUC 0-60 min ) after meal consumption was calculated. The HGI and LGI groups showed higher blood glucose and insulin AUC 0-60 min than the control group ( P < 0.001). At 60 min after the meal, the changes in blood pressure during SHG-ex were significantly greater in the HGI group, but not in the LGI group, than in the control group. The changes in blood pressure at the onset and end of SHG-ex 60 min after the meal were positively correlated with blood glucose AUC 0-60 min ( r = 0.321, P = 0.038; r = 0.402, P = 0.008, respectively) and plasma insulin AUC 0-60 min ( r = 0.339, P = 0.028; r = 0.302, P = 0.052, respectively). However, no association was observed during PEMI. These data suggest that postprandial hyperglycemia and hyperinsulinemia acutely exaggerate pressor response during SHG-ex in healthy young adults. NEW & NOTEWORTHY Postprandial hyperglycemia following consumption of a high-glycemic index (HGI) meal potentiated blood pressure response to static handgrip exercise (SHG-ex) in healthy young adults. These findings provide important insight into the role of the diet on acute circulatory response to exercise in healthy adults.

In almost all eubacteria, the AUA codon is translated by tRNA Ile2 bearing lysidine at the wobble position. Lysidine is introduced by tRNA Ile lysidine synthetase (TilS) via post-transcriptional modification of the cytidine of tRNA Ile2 (CAU). Lactobacillus casei and Lactobacillus plantarum have tilS homologues and tRNA Ile2 (CAU) genes. In addition, L. casei also has another tRNA Ile2 gene with an UAU anticodon. L. plantarum has a tRNA Ile (UAU)-like RNA. Here, we demonstrate that L. casei tRNA Ile2 (UAU) is charged with isoleucine by L. casei isoleucyl-tRNA synthetase (IleRS) but not by L. plantarum IleRS, even though the amino acid identity of these two enzymes is over 60%. It has been reported that, in Mycoplasma mobile, which has its tRNA Ile2 (UAU) but no tilS homologue, an Arg residue at position 865 of the IleRS is required for recognition of the UAU anticodon. This position is occupied by an Arg also in the IleRSs from both of the Lactobacillus species. Thus, other residues in L. casei, IleRS should also contribute to the recognition of tRNA Ile2 (UAU). We found that a chimeric L. casei IleRS in which the N-terminal domain was replaced by the corresponding region of L. plantatarum IleRS has very low aminoacylation activity towards both tRNA Ile2 (UAU) and tRNA Ile1 (GAU). The A18G mutant had barely detectable aminoacylation activity towards either of the tRNAs Ile . However, a double point mutant of A18G and G19N aminoacylated tRNA Ile1 (GAU), but not tRNA Ile2 (UAU). Our results suggest that, for L. casei IleRS, Ala18 and Gly19 also play a critical role in recognition of tRNA Ile2 (UAU)., (© 2022 Federation of European Biochemical Societies.)

Background: This study aims to compare the effects of soy protein isolate (SPI) and soy peptide (PEP) preload 30 min before a 75-g oral glucose tolerance test (OGTT) on the gastric emptying rate, plasma insulin, and blood glucose responses., Methods: Nine healthy young subjects were evaluated on four occasions. The participants consumed a 200-ml solution containing either 20 g of SPI or PEP in experiment 1. In experiment 2, 30 min after consuming either 20 g of SPI or PEP solutions, an OGTT was performed to evaluate the individual glycemic response. The gastric emptying rate was measured by the 13 C-sodium acetate breath test. Blood glucose and plasma insulin were measured before and after consuming either the SPI or PEP solutions and during the OGTT., Results: In experiment 1, plasma insulin levels were higher 30 min after consuming the PEP solution than after the SPI solution. PEP resulted in a faster gastric emptying rate than SPI. In experiment 2, just before performing the OGTT, the plasma insulin response was higher for PEP than for SPI. Fifteen minutes after starting the OGTT, the blood glucose response was lower after consuming PEP than after SPI. The gastric emptying rate tended to be faster after consuming PEP than after SPI (p = 0.08)., Conclusion: A PEP preload might be slightly more effective for the suppression of postprandial blood glucose excursion compared with SPI; thus, a PEP preload potentially induces an enhanced insulin response just before the OGTT., (© 2022. The Author(s).)

The relative influence of skin vascular conductance in glabrous (G; palm) and non-glabrous (NG; dorsal and forearm) regions to upstream brachial artery-shear stress (BA-SS) profile are unknown. This study aimed to elucidate the effects of G and/or NG skin vascular conductance (VC), which were modulated by warming or cooling manipulation, on BA-shear rate (SR, an estimate of SS) during cycling exercise. Seven healthy subjects performed 60-min exercise. Between 20 and 50 min of the exercise, the NG+G or G skin region were warmed to 42°C or cooled to 15°C using a water bath. Throughout the protocol, diameter and blood velocity in BA and skin VCs in forearm and palm were measured. All measurements showed that a steady-state response was reached after 20 min of exercise. Subsequently, during cooling manipulation, forearm VC was significantly decreased, and the concomitant BA-SR profile was revealed (primarily characterized by decreased antegrade SR and increased retrograde SR) in the NG+G. Such changes were not observed in G alone. During warming manipulation, forearm VC and mean BA-SR significantly increased only in the NG+G. In conclusion, vascular response in NG skin possibly plays a major role in the modulation of BA-SS profile during cycling exercise.

Hyperthermia during exercise in the heat causes minute ventilation ([Formula: see text]) to increase, which leads to reductions in arterial CO 2 partial pressure ([Formula: see text]) and cerebral blood flow. On the other hand, sodium bicarbonate ingestion reportedly results in metabolic alkalosis, leading to decreased [Formula: see text] and increased [Formula: see text] during prolonged exercise in a thermoneutral environment. Here, we investigated whether sodium bicarbonate ingestion suppresses heat-induced hyperventilation and the resultant hypocapnia and cerebral hypoperfusion during prolonged exercise in the heat. Eleven healthy men ingested a solution of sodium bicarbonate (0.3 g/kg body wt) (NaHCO 3 trial) or sodium chloride (0.208 g/kg) (NaCl trial). Ninety minutes after the ingestion, the subjects performed a cycle exercise for 60 min at 50% of peak oxygen uptake in the heat (35°C and 40% relative humidity). Esophageal temperature did not differ between the trials throughout ( P = 0.56, main effect of trial). [Formula: see text] gradually increased with exercise duration in the NaCl trial, but the increases in [Formula: see text] were attenuated in the NaHCO 3 trial ( P = 0.01, main effect of trial). Correspondingly, estimated [Formula: see text] and middle cerebral artery blood velocity (an index of anterior cerebral blood flow) were higher in the NaHCO 3 than the NaCl trial ( P = 0.002 and 0.04, main effects of trial). Ratings of perceived exertion were lower in the NaHCO 3 than the NaCl trial ( P = 0.02, main effect of trial). These results indicate that sodium bicarbonate ingestion mitigates heat-induced hyperventilation and reductions in [Formula: see text] and cerebral blood velocity during prolonged exercise in the heat. NEW & NOTEWORTHY Hyperthermia causes hyperventilation and concomitant hypocapnia and cerebral hypoperfusion. The cerebral hypoperfusion may underlie central fatigue. We demonstrate that sodium bicarbonate ingestion reduces heat-induced hyperventilation and attenuates hypocapnia-related cerebral hypoperfusion during prolonged exercise in the heat. In addition, we show that sodium bicarbonate ingestion reduces ratings of perceived exertion during the exercise. This study provides new insight into the development of effective strategies for preventing central fatigue during exercise in the heat.

Consumption of 2,4-decadienal (2,4-DD) delays gastric emptying (GE) rate in animals. Oil heating produces 2,4-DD and other aldehydes. Here we examined whether heated oil affects GE rate and food intake in humans, and whether it is mediated by 2,4-DD. In the first experiment, 10 healthy volunteers consumed 240-g pumpkin soup with 9.2 g of heated (HO) or non-heated corn oil (CO). Subsequently, 17 participants consumed pumpkin soup containing 3.1 g of either heated corn oil (HO), 1 mg 2,4-DD + non-heated corn oil (2,4-DD), or non-heated corn oil (CO). Sixty minutes following pumpkin soup, cod roe spaghetti was provided, and then energy intake was determined. To evaluate GE rate, 13 C breath test (Experiment 1) and ultrasonography (Experiments 1 and 2) were used. The results from the Experiment 1 confirmed that consumption of heated corn oil reduced GE rate. Experiment 2 showed a delayed GE rate in HO and 2,4-DD trials compared with CO trial ( p < 0.05). Energy intake was approximately 600-650 kJ lower in HO and 2,4-DD trials compared with CO trial ( p < 0.05). These findings suggest that 2,4-DD, either formed by oil heating or added to food, contributes to suppressing GE rate and energy intake.

Aim: We examined the effect of modulating the shear stress (SS) profile using forearm warming and cooling on subsequent endothelial function in the brachial artery (BA) during exercise., Methods: Twelve healthy young subjects immersed their right forearm in water (15 ℃ or 42 ℃) during a leg cycling exercise at 120-130 bpm for 60 min. The same exercise without water immersion served as a control. The BA diameter and blood velocity were simultaneously recorded using Doppler ultrasonography to evaluate the antegrade, retrograde, and mean shear rates (SRs, an estimate of SS) before, during, and after exercise. The endothelial function in the right BA was evaluated using flow-mediated dilation (FMD) (%) using two-dimensional high-resolution ultrasonography before (baseline) and 15 and 60 min after exercise., Results: During exercise, compared with the control trial, higher antegrade and mean SRs and lower retrograde SRs were observed in the warm trial; conversely, lower antegrade and mean SRs and higher retrograde SRs were observed in the cool trial. At 15 min postexercise, no significant change was observed in the FMD from baseline in the warm (Δ%FMD: +1.6%, tendency to increase; p = 0.08) and control trials (Δ%FMD: +1.1%). However, in the cool trial, the postexercise FMD at 60 min decreased from baseline (Δ%FMD: -2.7%) and was lower than that of the warm (Δ%FMD: +1.5%) and control (Δ%FMD: +1.2%) trials. Accumulated changes in each SR during and after exercise were significantly correlated with postexercise FMD changes., Conclusion: Modulation of shear profiles in the BA during exercise appears to be associated with subsequent endothelial function.

This study examined the effect of carbohydrate drink ingestion timing on gastrointestinal tract blood flow and motility after mild cycling exercise. Eight healthy participants were randomly assigned to ingest a liquid solution with 75 g glucose at either 5 min (PE-5) or 30 min (PE-30) after a single bout of leg cycling exercise according to target heart rate (approximately 120 beats/min). As the control trial (Con), participants ingested the same liquid solution without exercise. Celiac artery blood flow (BF), superior mesenteric artery BF, and gastric emptying rate were assessed by ultrasonography before and for 60 min after ingesting the glucose solution. Blood lactate, glucose, and plasma insulin were also measured at baseline and for 60 min after ingesting the glucose solution. Celiac artery BF significantly decreased from resting baseline immediately after exercise in both the PE-5 and PE-30 trials, and then returned to resting baseline just before the ingestion of glucose solution in the PE-30 trial. After ingesting the glucose solution, changes in celiac artery BF, superior mesenteric artery BF, % gastric emptying rate, blood lactate, blood glucose, and plasma insulin were not significantly different among the three trials. The timing of nutrient ingestion after mild exercise does not seem to impact the subsequent gastrointestinal motility, blood flow, and glycemic responses.

This study aimed to examine the carotid baroreflex (CBR) control of the central and peripheral hemodynamics after exercise using the neck pressure (NP) and neck suction (NS) technique. Sixteen healthy young male participants (age: 27 ± 1.5 yr) were in a supine position for 30 min preexercise, followed by 60 min of cycling exercise, and then returned to a supine position for an additional 60 min postexercise. Both pre- and postexercise, the CBR-mediated responses of the central and peripheral hemodynamics were evaluated using 5-s periods of NP and NS (-60, -40, or +40 mmHg). As the central hemodynamics measurements, heart rate (HR), mean arterial pressure (MAP), cardiac output, and total vascular conductance were assessed. To determine peripheral circulation, vascular conductance in active and inactive limbs was measured. Eight participants [responder (RE) group] showed substantial postexercise hypotension (PEH) during recovery from exercise (Δ MAP: approximately -5 ± 0.9 mmHg, P < 0.05). The other eight participants did not display a reduction in MAP after exercise (non-RE group). In the non-RE group, the responsiveness of CBR-mediated changes in HR, MAP, and vascular conductance increased, particularly in response to -40 mmHg NS during postexercise compared with preexercise. However, in the RE group, any alterations in responsiveness to NP and NS were unchanged during PEH compared with preexercise. In conclusion, some normotensive individuals do not show PEH because the responsiveness of the CBR in central and peripheral hemodynamics following exercise is augmented, particularly to high blood pressure. NEW & NOTEWORTHY The carotid baroreflex (CBR) control of central and peripheral hemodynamics was investigated after exercise in both the presence and absence of postexercise hypotension (PEH). In individuals with no PEH, the responsiveness of CBR-mediated changes in all hemodynamics was augmented after exercise, particularly to high blood pressure; conversely, the CBR responsiveness remained unchanged in individuals with PEH. These findings provide insight into the mechanism of CBR control after exercise.