This study compared the effects of ingesting water (WATER), an 8.6% glucose solution (GLU) and an 8.6% glucose+fructose solution (2:1 ratio, GLU+FRU) on gastric emptying (GE), fluid delivery, and markers of hydration status during moderate intensity exercise. Eight male subjects (age=24 +/- 2 years, weight=74.5 +/- 1.2 kg, VO(2max)=62.6 +/- 2.5 mL/kg/min) performed three 120 min cycling bouts at 61% VO(2max)). Subjects ingested GLU, GLU+FRU (both delivering 1.5 g/min carbohydrate), or WATER throughout exercise, ingesting 2.1 L. Serial dye dilution measurements of GE were made throughout exercise and subjects ingested 5.00 g of D(2)O and 150 mg of (13)C-acetate at 60 min to obtain measures of fluid uptake and GE, respectively. GLU+FRU resulted in faster rates of deuterium accumulation, an earlier time to peak in the (13)C enrichment of expired air and a faster rate of GE compared with GLU. GLU+FRU also attenuated the rise in heart rate that occurred in GLU and WATER and resulted in lower ratings of perceived exertion. There was a greater loss in body weight with GLU corrected for fluid intake. These data suggest that ingestion of a combined GLU+FRU solution increases GE and "fluid delivery" compared with a glucose only solution.

The purpose of this study was to assess the level of agreement between two techniques commonly used to measure exogenous carbohydrate oxidation (CHO(EXO)). To accomplish this, seven healthy male subjects (24 +/- 3 yr, 74.8 +/- 2.1 kg, V(O2(max)) 62 +/- 4 ml x kg(-1) x min(-1)) exercised at 50% of their peak power for 120 min on two occasions. During these exercise bouts, subjects ingested a solution containing either 144 g glucose (8.7% wt/vol glucose) or water. The glucose solution contained trace amounts of both [U-13C]glucose and [U-14C]glucose to allow CHO(EXO) to be quantified simultaneously. The water trial was used to correct for background 13C enrichment. 13C appearance in the expired air was measured using isotope ratio mass spectrometry, whereas 14C appearance was quantified by trapping expired CO(2) in solution (using hyamine hydroxide) and adding a scintillator before counting radioactivity. CHO(EXO) measured with [13C]glucose ([13C]CHO(EXO)) was significantly greater than CHO(EXO) measured with [14C]glucose ([14C]CHO(EXO)) from 30 to 120 min. There was a 15 +/- 4% difference between [13C]CHO(EXO) and [14C]CHO(EXO) such that the absolute difference increased with the magnitude of CHO(EXO). Further investigations suggest that the difference is not because of losses of CO2 from the trapping solution before counting or an underestimation of the "strength" of the trapping solution. Previous research suggests that the degree of isotopic fractionation is small (S. C. Kalhan, S. M. Savin, and P. A. Adam. J Lab Clin Med89: 285-294, 1977). Therefore, the explanation for the discrepancy in calculated CHO(EXO) remains to be fully understood.

The purposes of this study were: 1) to obtain a measure of exogenous carbohydrate (CHO(Exo)) oxidation and plasma glucose kinetics during 5 h of exercise; and 2) to compare CHO(Exo) following the ingestion of a glucose solution (Glu) or a glucose + fructose solution (2:1 ratio, Glu+Fru) during ultraendurance exercise. Eight well-trained subjects exercised three times for 5 h at 58% maximum O2 consumption while ingesting either Glu or Glu+Fru (both delivering 1.5 g/min CHO) or water. The CHO used had a naturally high 13C enrichment, and five subjects received a primed continuous intravenous [6,6-2H2]glucose infusion. CHO(Exo) rates following the ingestion of Glu leveled off after 120 min and peaked at 1.24 +/- 0.04 g/min. The ingestion of Glu+Fru resulted in a significantly higher peak rate of CHO(Exo) (1.40 +/- 0.08 g/min), a faster rate of increase in CHO(Exo), and an increase in the percentage of CHO(Exo) oxidized (65-77%). However, the rate of appearance and disappearance of Glu continued to increase during exercise, with no differences between trials. These data suggest an important role for gluconeogenesis during the later stages of exercise. Following the ingestion of Glu+Fru, cadence (rpm) was maintained, and the perception of stomach fullness was reduced relative to Glu. The ingestion of Glu+Fru increases CHO(Exo) compared with the ingestion of Glu alone, potentially through the oxidation of CHO(Exo) in the liver or through the conversion to, and oxidation of, lactate.

The aim of this experiment was to compare the efficiency of elite cyclists with that of trained and recreational cyclists. Male subjects (N = 69) performed an incremental exercise test to exhaustion on an electrically braked cycle ergometer. Cadence was maintained between 80 - 90 rpm. Energy expenditure was estimated from measures of oxygen uptake (VO2) and carbon dioxide production (VCO2) using stoichiometric equations. Subjects (age 26 +/- 7 yr, body mass 74.0 +/- 6.3 kg, Wpeak 359 +/- 40 W and VO(2)peak 62.3 +/- 7.0 mL/kg/min) were divided into 3 groups on the basis of their VO(2)peak (< 60.0 (Low, N = 26), 60 - 70 (Med, N = 27) and > 70 (High, N = 16) mL/kg/min). All data are mean +/- SE. Despite the wide range in aerobic capacities gross efficiency (GE) at 165 W (GE(165)), GE at the same relative intensity (GE(final)), delta efficiency (DE) and economy (EC) were similar between all groups. Mean GE(165) was 18.6 +/- 0.3 %, 18.8 +/- 0.4 % and 17.9 +/- 0.3 % while mean DE was 22.4 +/- 0.4 %, 21.6 +/- 0.4 % and 21.2 +/- 0.5 % (for Low, Medium and High, respectively). There was no correlation between GE(165), GE(final), DE or EC and VO(2)peak. Based on these data, we conclude that there are no differences in efficiency and economy between elite cyclists and recreational level cyclists.

The aim of this study was to determine whether consumption of a diet containing 8.5 g carbohydrate (CHO) x kg(-1) x day(-1) (high CHO; HCHO) compared with 5.4 g CHO x kg(-1) x day(-1) (control; Con) during a period of intensified training (IT) would result in better maintenance of physical performance and mood state. In a randomized cross-over design, seven trained runners [maximal O(2) uptake (Vo(2 max)) 64.7 +/- 2.6 ml x kg(-1) x min(-1)] performed two 11-day trials consuming either the Con or the HCHO diet. The last week of both trials consisted of IT. Performance was measured with a preloaded 8-km all-out run on the treadmill and 16-km all-out runs outdoors. Substrate utilization was measured using indirect calorimetry and continuous [U-(13)C]glucose infusion during 30 min of running at 58 and 77% Vo(2 max). Time to complete 8 km was negatively affected by the IT: time significantly increased by 61 +/- 23 and 155 +/- 38 s in the HCHO and Con trials, respectively. The 16-km times were significantly increased (by 8.2 +/- 2.1%) during the Con trial only. The Daily Analysis of Life Demands of Athletes questionnaire showed significant deterioration in mood states in both trials, whereas deterioration in global mood scores, as assessed with the Profile of Mood States, was more pronounced in the Con trial. Scores for fatigue were significantly higher in the Con compared with the HCHO trial. CHO oxidation decreased significantly from 1.7 +/- 0.2 to 1.2 +/- 0.2 g/min over the course of the Con trial, which was completely accounted for by a decrease in muscle glycogen oxidation. These findings indicate that an increase in dietary CHO content from 5.4 to 8.5 g CHO x kg(-1)x day(-1) (41 vs. 65% total energy intake, respectively) allowed better maintenance of physical performance and mood state over the course of training, thereby reducing the symptoms of overreaching.

The purpose of the present study was to examine the effect of pre-exercise carbohydrate (CHO) ingestion on circulating leukocyte numbers, plasma interleukin (IL)-6, plasma cortisol, and lipopolysaccharide (LPS)-stimulated neutrophil degranulation responses in moderately trained male cyclists who completed approximately 1-h of high-intensity cycling. The influence of the timing of pre-exercise CHO ingestion was investigated in 8 subjects who consumed 75 g CHO as a glucose solution at either 15 (-15 trial), or 75 (-75 trial) min before the onset of exercise. The influence of the amount of pre-exercise CHO ingestion was investigated in a further 10 subjects who consumed either 25 g or 200 g CHO as a glucose solution or a placebo 45 min before the onset of exercise. At the onset of exercise in the timing experiment, the plasma glucose concentration was significantly (p < .05) lower on the -75 trial compared with pre-drink values, and the plasma cortisol concentration and neutrophil to lymphocyte (N/L) ratio were significantly (p < .05) elevated in the post-exercise period. In the -15 trial, plasma glucose level was well maintained, and the plasma cortisol concentration and N/L ratio were not significantly elevated above resting levels. However, LPS-stimulated neutrophil degranulation was similar in the -15 and -75 trials. The amount of CHO ingested had no effect on the magnitude of the rise in the N/L ratio compared with placebo when consumed 45 min pre-exercise. Finally, although an exercise-induced increase in the plasma IL-6 concentration was observed, this effect was independent of pre-exercise CHO ingestion.

PURPOSE The aim of this study was to determine if a high-carbohydrate (HCHO) compared to a control (CON) diet during a period of intensified training would prevent the development of overreaching. METHODS In a randomized cross-over design, the training of 7 trained male runners (VO2max 64.7 ± 2.6 ml/kg/min) was intensified for 7 days, after 4 days of normal training. On three days, subjects ran 60min steady state on a treadmill followed by a self-paced 8km all out run and on four days they ran 16km all out. During the two trials they consumed either a HCHO (8.5 ± 0.2 g CHO/kg/d) or a CON-diet (5.4 ± 0.1 g CHO/kg/d). Substrate utilization was measured using indirect calorimetry on day 1 and 11 and glucose kinetics were studied using a primed continuous [U-13C]-glucose infusion during 30 min of running at 58% VO2max and 30 min at 77% VO2max on day 11. RESULTS Time to complete 8km was significantly increased by 61 ± 23s in the HCHO-trial and by 155 ± 38s in the CON-trial. The 16km times were only significantly increased during the CON diet (8.2 ± 2.1%). Increases in global mood scores as assessed with the POMS were more marked in the CON-trial than the HCHO-trial. Training resulted in 7 ± 2 and 13 ± 2 fold increases in fatigue scores during the HCHO and CON-trials resp. During exercise at 58% VO2max, CHO oxidation decreased significantly from 1.7 ± 0.2 to 1.2 ± 0.2 g/min over the course of the CON-trial, while no changes were seen in the HCHO trial. On day 11, muscle glycogen oxidation was significantly higher during the HCHO trial compared to the CON trial at 58% VO2max (1.7 ± 0.2 vs 1.0 ± 0.1 g/min) and at 77% VO2max (2.2 ± 0.2 vs 1.2 ± 0.2 g/min). CONCLUSION The decrease in CHO oxidation during 7 days of CON was completely accounted for by a decrease in muscle glycogen oxidation. The findings indicate that during a period of intensified running training consuming a HCHO diet compared to a CON diet reduces the symptoms of overreaching, but it cannot prevent it. Supported by a grant of the Chemical Biological Defence and Human Sciences Domain of the UK MOD's CRP

The purpose of the present study was to examine whether combined ingestion of a large amount of fructose and glucose during cycling exercise would lead to exogenous carbohydrate oxidation rates >1 g/min. Eight trained cyclists (maximal O(2) consumption: 62 +/- 3 ml x kg(-1) x min(-1)) performed four exercise trials in random order. Each trial consisted of 120 min of cycling at 50% maximum power output (63 +/- 2% maximal O(2) consumption), while subjects received a solution providing either 1.2 g/min of glucose (Med-Glu), 1.8 g/min of glucose (High-Glu), 0.6 g/min of fructose + 1.2 g/min of glucose (Fruc+Glu), or water. The ingested fructose was labeled with [U-(13)C]fructose, and the ingested glucose was labeled with [U-(14)C]glucose. Peak exogenous carbohydrate oxidation rates were approximately 55% higher (P < 0.001) in Fruc+Glu (1.26 +/- 0.07 g/min) compared with Med-Glu and High-Glu (0.80 +/- 0.04 and 0.83 +/- 0.05 g/min, respectively). Furthermore, the average exogenous carbohydrate oxidation rates over the 60- to 120-min exercise period were higher (P < 0.001) in Fruc+Glu compared with Med-Glu and High-Glu (1.16 +/- 0.06, 0.75 +/- 0.04, and 0.75 +/- 0.04 g/min, respectively). There was a trend toward a lower endogenous carbohydrate oxidation in Fruc+Glu compared with the other two carbohydrate trials, but this failed to reach statistical significance (P = 0.075). The present results demonstrate that, when fructose and glucose are ingested simultaneously at high rates during cycling exercise, exogenous carbohydrate oxidation rates can reach peak values of approximately 1.3 g/min.

Rebound hypoglycemia has been reported after pre-exercise carbohydrate (CHO) ingestion in some studies but not in others. Differences in the experimental design and factors such as the exercise intensity are likely to be responsible for the discrepancies between these studies. Exercise intensity might be a crucial factor since it affects both insulinemia, liver glucose production and muscle glucose uptake. Purpose: Therefore the aim of the present study was to compare the glycemic and insulinemic responses to exercise at different intensities after ingestion of a standardized pre-exercise CHO load. Methods: Eight trained subjects (VO2max 58.4 ± 1.9 ml/kg/min) consumed 75g of glucose 45min prior to 20min of exercise at 55 ± 1, 77 ± 1 and 90 ± 1%VO2max. Blood samples were collected before glucose ingestion, at 15min intervals at rest and 5min intervals during exercise. Results: There were no significant differences in glucose or insulin concentrations between the three trials during exercise. Immediately pre-exercise, plasma glucose concentration had returned to pre-ingestion levels, while the insulin concentration was more than 3 times higher than pre-ingestion (45 ± 10, 62 ± 14, 62 ± 15 vs 16 ± 2, 16 ± 2, 16 ± 1 μU/mL for the 55%, 77% and 90% trials resp.). During exercise, plasma glucose concentration decreased from 4.7 ± 0.3, 5.5 ± 0.3, 4.8 ± 0.3 mmol/L before the start of exercise to 4.1 ± 0.2, 4.0 ± 0.2, 4.1 ± 0.2 mmol/L during the first 5min in the 55%, 77% and 90% trials respectively and then stabilized in all trials. During the 55% and 77% trials, 3 subjects developed hypoglycemia (glucose concentration < 3.5mmol/L), while hypoglycemia occurred in 4 subjects during the 90% trial. Insulin concentrations decreased during the first 10min of exercise and then leveled off at pre-ingestion concentrations. Conclusions: These data suggest that the glycemic response to 75g of CHO 45min pre-exercise is similar during exercise of different intensities. The discrepancies found in studies regarding hypoglycemia after pre-exercise CHO feedings cannot therefore be explained by differences in exercise intensity employed in those studies.

Background: Carbohydrate intake before exercise may result in hypoglycemia. The development of this hypoglycemia may depend on the timing of carbohydrate intake. Purpose: To investigate the metabolic and performance responses to pre-exercise carbohydrate feedings ingested different times before exercise. Methods: Eight subjects (28 ± 3yr, 74.5 ± 2.6kg, VO2max 63.1 ± 3.1mL/kg/min) arrived in the lab following an overnight fast and ingested a bolus of 75g of glucose in 500mL water. Thereafter they rested for 15, 45 or 75min (15-Pre, 45-Pre or 75-Pre) before exercising for 20min at 65% Wmax followed immediately by a time trial (685 ± 18kJ). Results: There were no differences in performance between conditions (mean power 268 ± 10, 269 ± 7 and 276 ± 12W for 15-Pre, 45-Pre and 75-Pre). There were significant differences between 15-Pre and 45-Pre/75-Pre in plasma glucose and between all conditions in insulin concentrations at the onset of exercise (glucose 6.6 ± 0.6, 4.5 ± 0.2 and 3.7 ± 0.2mmol/L respectively, insulin 72.6 ± 10.4, 50.8 ± 9.9 and 33.9 ± 5.5μU/mL respectively, p < 0.05). These differences disappeared within 10 min of exercise. No subjects became hypoglycemic (plasma glucose < 3.5mmol/L) in the 15-Pre trial while 3 and 5 subjects were transiently hypoglycemic in the 45-Pre and 75-Pre conditions respectively. However performance and ratings of perceived did not seem to be related to hypoglycemia. Conclusion: 15 and 75min delays resulted in glucose and insulin concentrations that were respectively higher and lower at the onset of exercise than those caused by a 45min delay. These differences disappeared within 10min of exercise and had no effect on performance. Although hypoglycemia was observed in some subjects during the first 10min, this did not seem to be related to performance.

PURPOSE:The aim of this experiment was to establish the reproducibility of gross efficiency (GE), delta efficiency (DE), and economy (EC) during a graded cycle ergometer test in seventeen male subjects.METHODS:All subjects performed three identical exercise tests at a constant pedal cadence of 80 rpm on an electrically braked cycle ergometer. Energy expenditure was estimated from measures of oxygen uptake (VO(2)) and carbon dioxide production (VCO(2)) by using stoichiometric equations.RESULTS:The subjects characteristics were age 24 +/- 6 yr, body mass 74.6 +/- 6.9 kg, body fat 13.9 +/- 2.2%, and VO(2max) 61.9 +/- 2.4 mL x kg(-1) x min(-1) (all means +/- SD). Average GE, DE, and EC for the three tests were 19.8 +/- 0.6%, 25.8 +/- 1.5%, and 5.0 +/- 0.1 kJ x L(-1), respectively. The coefficients of variation (confidence limits) were GE 4.2 (3.2-6.4)%, DE 6.7 (5.0-10.0)%, and EC 3.3 (2.4-4.9)%. GE was significantly lower at 95 W and 130 W when compared with 165 W, 200 W, 235 W, 270 W, and 305 W. GE at 165 W was significantly lower (P < 0.05) that GE at 235 W. A weak correlation (r = 0.491; P < 0.05) was found between peak oxygen uptake (VO(2peak)) and GE, whereas no correlations were found between VO(2max) and DE or EC.CONCLUSION:We conclude that a graded exercise test with 3-min stages and 35-W increments is a method by which reproducible measurements of both GE and EC can be obtained, whereas measurements of DE seemed slightly more variable.

The aim of this experiment was to investigate a possible relationship between aerobic capacity (VO2peak) and gross efficiency (GE) during submaximal cycling. 73 subjects with VO2peak values ranging from 45.1 to 83.1 ml.kg−1.min−1 performed an incremental exercise test to exhaustion on a cycle ergometer beginning at 95 W and increasing by 35 W every 3 minutes. Cadence was maintained between 80–90 rpm. Oxygen uptake was averaged over the last two minutes of each stage. Subjects were divided into three groups by VO2peak corresponding to <60 ml.kg−1.min−1 (L, n = 27), 60–70 ml.kg−1.min−1 (M, n = 33) and >70ml.kg−1.min−1 (H, n = 13). GE was averaged for all workloads between 50–70% VO2peak. All data is presented as mean ± SD. Mean VO2peak (ml.kg−1.min−1) was significantly different between the groups (L = 55.3 ± 6.2, M = 63.4 ± 5.7, H = 75.5 ± 9.6, F2,70 = 128.7, p < 0.01). Despite a wide range of aerobic capacities there was no correlation between VO2peak and mean GE (r = 0.156, p = 0.188). One-way ANOVA revealed no significant differences in GE (%) between the groups (L = 18.6 ± 1.0, M = 18.8 ± 1.5, H = 18.9 ± 1.0, F2,70 = 0.322, p = 0.726). These data suggest that aerobic capacity is not related to gross efficiency.