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  • Author: Kym J. Guelfi x
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Sharon Gam, Kym J. Guelfi and Paul A. Fournier

Studies have reported that rinsing the mouth with a carbohydrate (CHO) solution improves cycling time-trial performance compared with rinsing with a placebo solution. However, no studies have compared the effect of mouth rinsing with a no-mouth-rinse control condition. The aim of this study was to compare the effects of a CHO mouth rinse with those of a placebo rinse and a no-rinse condition. Ten male cyclists completed three 1,000-kJ cycling time trials in a randomized, counterbalanced order. At every 12.5% of the time trial completed, participants were required to rinse their mouths for 5 s with either a 6.4% maltodextrin solution (CHO), water (WA), or no solution (CON). Heart rate and ratings of perceived exertion (RPE) were recorded every 25% of the time trial completed. Time to completion was faster in both CHO (65.7 ± 11.07 min) and CON (67.6 ± 12.68 min) than in WA (69.4 ± 13.81 min; p = .013 and p = .042, respectively). The difference between CHO and CON approached significance (p = .086). There were no differences in heart rate or RPE between any conditions. In summary, repeated mouth rinsing with water results in decreased performance relative to not rinsing at all. Adding CHO to the rinse solution appears to oppose this fall in performance, possibly providing additional benefits to performance compared with not rinsing the mouth at all. This brings into question the magnitude of the effect of CHO mouth rinsing reported in previous studies that did not include a no-rinse condition.

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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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Katriona J.M O’Donoghue, Paul A. Fournier and Kym J. Guelfi

Although the manipulation of exercise and dietary intake to achieve successful weight loss has been extensively studied, it is unclear how the time of day that exercise is performed may affect subsequent energy intake. The purpose of the current study was to investigate the effect of an acute bout of exercise performed in the morning compared with an equivalent bout of exercise performed in the afternoon on short-term energy intake. Nine healthy male participants completed 3 trials: morning exercise (AM), afternoon exercise (PM), or control (no exercise; CON) in a randomized counterbalanced design. Exercise consisted of 45 min of treadmill running at 75% VO2peak. Energy intake was assessed over a 26-hr period with the participants eating ad libitum from a standard assortment of food items of known quantity and composition. There was no significant difference in overall energy intake (M ± SD; CON 23,505 ± 6,938 kJ, AM 24,957 ± 5,607 kJ, PM 24,560 ± 5,988 kJ; p = .590) or macronutrient preferences during the 26-hr period examined between trials. Likewise, no differences in energy intake or macronutrient preferences were observed at any of the specific individual meal periods examined (i.e., breakfast, lunch, dinner) between trials. These results suggest that the time of day that exercise is performed does not significantly affect short-term energy intake in healthy men.

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Jessica S. West, Tom Ayton, Karen E. Wallman and Kym J. Guelfi

Ingestion of an acute dose of phosphate has been shown to attenuate energy intake in the subsequent meal. This raises the question of whether the practice of phosphate supplementation over a number of days by athletes to enhance performance also influences energy intake. This study investigated the effect of 6 d of phosphate supplementation on appetite and energy intake, as well as aerobic capacity, in trained individuals. Twenty participants completed two 6-d phases of supplementation with either sodium phosphate (50 mg/kg of fat-free mass per day) or a placebo in a double-blinded, counterbalanced design. On Days 1, 2, and 6 of supplementation, a laboratory meal was provided to assess appetite and ad libitum energy intake. All other food and drink consumed during each supplementation phase were recorded in a food diary. After the 6 d of supplementation, peak aerobic capacity (VO2peak) was assessed. There was no difference in energy intake at the laboratory meal after an acute dose (i.e., on Day 1; placebo 2,471 ± 919 kJ, phosphate 2,353 ± 987 kJ; p = .385) or prolonged supplementation with sodium phosphate (p = .581) compared with placebo. Likewise, there was no difference in VO2peak with phosphate supplementation (placebo 52.6 ± 5.2 ml · kg−1 · min−1, phosphate 53.3 ± 6.1 ml · kg−1 · min−1; p = .483). In summary, 6 d of sodium phosphate supplementation does not appear to influence energy intake. Therefore, athletes supplementing with sodium phosphate can do so without hindering their nutritional status. However, given that phosphate supplementation failed to improve aerobic capacity, the ergogenic benefit of this supplement remains questionable.

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Cameron P. Brewer, Brian Dawson, Karen E. Wallman and Kym J. Guelfi

Research into supplementation with sodium phosphate has not investigated the effects of a repeated supplementation phase. Therefore, this study examined the potential additive effects of repeated sodium phosphate (SP) supplementation on cycling time-trial performance and peak oxygen uptake (VO2peak). Trained male cyclists (N = 9, M ± SD VO2peak = 65.2 ± 4.8 ml · kg−1 · min−1) completed baseline 1,000-kJ time-trial and VO2peak tests separated by 48 hr, then ingested either 50 mg · kg fat-free mass−1 · d−1 of tribasic SP or a combined glucose and NaCl placebo for 6 d before performing these tests again. A 14-d washout period separated the end of one loading phase and the start of the next, with 2 SP and 1 placebo phase completed in a counterbalanced order. Although time-trial performance (55.3–56.5 min) was shorter in SP1 and SP2 (~60–70 s), effect sizes and smallest-worthwhile-change values did not differ in comparison with baseline and placebo. However, mean power output was greater than placebo during time-trial performance at the 250-kJ and 500-kJ time points (p < .05) after the second SP phase. Furthermore, mean VO2peak values (p < .01) were greater after the SP1 (3.5–4.3%), with further improvements (p < .01) found in SP2 (7.1–7.7%), compared with baseline and placebo. In summary, repeated SP supplementation, ingested either 15 or 35 d after initial loading, can have an additive effect on VO2peak and possibly time-trial performance.

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Penelope S. Larsen, Cheyne E. Donges, Kym J. Guelfi, Greg C. Smith, David R. Adams and Rob Duffield

Aerobic exercise (AE) and strength exercise (SE) are reported to induce discrete and specific appetite-related responses; however, the effect of combining AE and SE (i.e., combined exercise; CE) remains relatively unknown. Twelve inactive overweight men (age: 48 ± 5 y; BMI: 29.9 ± 1.9 kg∙m2) completed four conditions in a random order: 1) nonexercise control (CON) (50 min seated rest); 2) AE (50 min cycling; 75% VO2peak); 3) SE (10 × 8 leg extensions; 75% 1RM); and 4) CE (50% SE + 50% AE). Perceived appetite, and appetiterelated peptides and metabolites were assessed before and up to 2 h postcondition (0P, 30P, 60P, 90P, 120P). Perceived appetite did not differ between trials (p < .05). Acylated ghrelin was lower at 0P in AE compared with CON (p = .039), while pancreatic polypeptide (PP) was elevated following AE compared with CON and CE. Glucose-dependent insulinotropic peptide (GIPtotal) was greater following all exercise conditions compared with CON, as was glucagon, although concentrations were generally highest in AE (p < .05). Glucose was acutely increased with SE and AE (p < .05), while insulin and C-peptide were higher after SE compared with all other conditions (p < .05). In inactive, middle-aged men AE, SE and CE each have their own distinct effects on circulating appetite-related peptides and metabolites. Despite these differential exercise-induced hormone responses, exercise mode appears to have little effect on perceived appetite compared with a resting control in this population.