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Laís Monteiro Rodrigues Loureiro, Caio Eduardo Gonçalves Reis and Teresa Helena Macedo da Costa

involved in the process of glycogen synthesis. Adenosine monophosphate-activated protein kinase (AMPK) is an enzyme responsible for the translocation of glucose transporter 4 (GLUT-4) to the cell membrane when activated by skeletal muscle contraction ( Mu et al., 2001 ; Stapleton et al., 1996 ). AMPK

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Rachel B. Parks, Hector F. Angus, Douglas S. King and Rick L. Sharp

synergistic actions of insulin and muscle contractions stimulated GLUT4 translocation until counterregulatory hormones normalized blood glucose by ∼30 min into exercise ( Defronzo et al., 1981 ; Hargreaves et al., 1987 ). However, subsequent studies could not replicate the results, instead finding

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Xiaomin Sun, Zhen-Bo Cao, Kumpei Tanisawa, Satomi Oshima and Mitsuru Higuchi

football ( Guo et al., 2013 ; Murata et al., 2016 ; Selden et al., 2009 ) athletes, who often intentionally try to increase their body mass as a means of performance enhancement. Selden et al. ( 2009 ) reported that players from the National Football League have higher fasting glucose concentrations

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Ilkka Heinonen, Jukka Kemppainen, Toshihiko Fujimoto, Juhani Knuuti and Kari K. Kalliokoski

metabolism of human bone marrow increases from a resting state to low-intensity exercise ( Heinonen et al., 2013a ). Furthermore, measurement of glucose uptake (GU) by 18 F-fluorodeoxyglucose (FDG) in mouse bone at rest demonstrated that relative to other tissues, bone accumulated a significant fraction of

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Erik A. Richter, Jørgen F.P. Wojtaszewski, Søren Kristiansen, Jens R. Daugaard, Jakob N. Nielsen, Wim Derave and Bente Kiens

In the present short review some factors affecting glucose utilization during exercise in skeletal muscle will be briefly described. Special focus will be put on the glucose transport step across the sarcolemma. Glucose transporters (GLUT4) are expressed at a surprisingly similar level in the different muscle fiber types in human skeletal muscle in contrast to findings in the rat. When working at the same absolute work load muscle glucose transport is decreased in trained compared with untrained muscle in part due to a decrease in GLUT4 translocation to the sarcolemma in trained muscle. However, when trained and untrained muscle are stressed severely by a workload taxing 100% of their peak oxygen uptake in a glycogen-depleted state, then glucose uptake is larger in trained than in untrained muscle and correlates with muscle GLUT4 content. Finally, the possible role of the AMP-activated protein kinase (AMPK) in regulating glucose uptake during exercise is discussed. It is indicated that at present no experiments definitively link activation of AMPK to activation of muscle glucose transport during exercise.

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Stephen P. Bailey, Julie Hibbard, Darrin La Forge, Madison Mitchell, Bart Roelands, G. Keith Harris and Stephen Folger

examined differences in exercise performance, comparing glucose and maltodextrin MR with artificial sweeteners in elite cyclists. These investigators found that cycle time-trial performance times were significantly improved when either 6.4% glucose or maltodextrin rinse was used prior to exercise. During

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Andrew R. Coggan, Robert J. Spina, Wendy M. Kohrt, Dennis M. Bier and John O. Holloszy

We hypothesized that when plasma glucose availability is maintained by carbohydrate (CHO) ingestion, trained cyclists can utilize plasma glucose at very high rates during the later stages of prolonged exercise (10). To test this hypothesis, a well-trained male cyclist was studied during exercise to fatigue at 70% VO2max when ingesting glucose throughout exercise. A primed continuous infusion of [U-13C]glucose was begun after 60 min of exercise to measure rates of plasma glucose appearance (Ra), disappearance (Rd), and oxidation (Rox). Ra and Rd rose progressively throughout exercise, peaking at 6.85 and 6.99 mmollmin, respectively, at fatigue (i.e., 133 min). Most (93%) of this glucose was oxidized; during the final 30 min of exercise, Rox, averaged 6.10 mmollmin and accounted for approximately half of total CHO oxidation. These results support the hypothesis that trained cyclists can oxidize plasma glucose at very high rates during the later stages of prolonged exercise when fed CHO.

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Edwin Chong, Kym J. Guelfi and Paul A. Fournier

This study investigated whether combined ingestion and mouth rinsing with a carbohydrate solution could improve maximal sprint cycling performance. Twelve competitive male cyclists ingested 100 ml of one of the following solutions 20 min before exercise in a randomized double-blinded counterbalanced order (a) 10% glucose solution, (b) 0.05% aspartame solution, (c) 9.0% maltodextrin solution, or (d) water as a control. Fifteen min after ingestion, repeated mouth rinsing was carried out with 11 × 15 ml bolus doses of the same solution at 30-s intervals. Each participant then performed a 45-s maximal sprint effort on a cycle ergometer. Peak power output was significantly higher in response to the glucose trial (1188 ± 166 W) compared with the water (1036 ± 177 W), aspartame (1088 ± 128 W) and maltodextrin (1024 ± 202W) trials by 14.7 ± 10.6, 9.2 ± 4.6 and 16.0 ± 6.0% respectively (p < .05). Mean power output during the sprint was significantly higher in the glucose trial compared with maltodextrin (p < .05) and also tended to be higher than the water trial (p = .075). Glucose and maltodextrin resulted in a similar increase in blood glucose, and the responses of blood lactate and pH to sprinting did not differ significantly between treatments (p > .05). These findings suggest that combining the ingestion of glucose with glucose mouth rinsing improves maximal sprint performance. This ergogenic effect is unlikely to be related to changes in blood glucose, sweetness, or energy sensing mechanisms in the gastrointestinal tract.

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Alan J. McCubbin, Anyi Zhu, Stephanie K. Gaskell and Ricardo J.S. Costa

guidelines during prolonged endurance exercise (>2.5 hr) suggest that up to 90 g/hr be consumed by combining glucose and/or its polymers with fructose ( Thomas et al., 2016 ). This approach is recommended to maximize exogenous carbohydrate provision, while aiming to minimize exercise

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Darren Triplett, J. Andrew Doyle, Jeffrey C. Rupp and Dan Benardot

A number of recent research studies have demonstrated that providing glucose and fructose together in a beverage consumed during exercise results in significantly higher oxidation rates of exogenous carbohydrate (CHO) than consuming glucose alone. However, there is insufficient evidence to determine whether the increased exogenous CHO oxidation improves endurance performance. The purpose of this study was to determine whether consuming a beverage containing glucose and fructose (GF) would result in improved cycling performance compared with an isocaloric glucose-only beverage (G). Nine male competitive cyclists (32.6 ± 5.8 years, peak oxygen uptake 61.5 ± 7.9 ml · kg-1 · min-1) completed a familiarization trial and then 2 simulated 100-km cycling time trials on an electronically braked Lode cycle ergometer separated by 5–7 d. During the randomly ordered experimental trials, participants received 36 g of CHO of either G or GF in 250 ml of water every 15 min. All 9 participants completed the 100-km time trial significantly faster when they received the GF beverage than with G (204.0 ± 23.7 vs. 220.6 ± 36.6 min; p = .023). There was no difference at any time point between trials for blood glucose or for blood lactate. Total CHO oxidation increased significantly from rest during exercise but was not statistically significant between the GF and G trials, although there was a trend for CHO oxidation to be higher with GF in the latter stages of the time trial. Consumption of a CHO beverage containing glucose and fructose results in improved 100-km cycling performance compared with an isocaloric glucose-only beverage.