Postexercise muscle glycogen synthesis with glucose, galactose, and combined galactose-glucose ingestion.

Ingested galactose can enhance postexercise liver glycogen repletion when combined with glucose but effects on muscle glycogen synthesis are unknown. In this double-blind randomized study participants [7 men and 2 women; V̇o2max: 51.1 (8.7) mL·kg-1·min-1] completed three trials of exhaustive cycling exercise followed by a 4-h recovery period, during which carbohydrates were ingested at the rate of 1.2 g·kg-1·h-1 comprising glucose (GLU), galactose (GAL) or galactose + glucose (GAL + GLU; 1:2 ratio). The increase in vastus lateralis skeletal-muscle glycogen concentration during recovery was higher with GLU relative to GAL + GLU [contrast: +50 mmol·(kg DM)-1; 95%CL 10, 89; P = 0.021] and GAL [+46 mmol·(kg DM)-1; 95%CL 8, 84; P = 0.024] with no difference between GAL + GLU and GAL [-3 mmol·(kg DM)-1; 95%CL -44, 37; P = 0.843]. Plasma glucose concentration in GLU was not significantly different vs. GAL + GLU (+ 0.41 mmol·L-1; 95%CL 0.13, 0.94) but was significantly lower than GAL (-0.75 mmol·L-1; 95%CL -1.34, -0.17) and also lower in GAL vs. GAL + GLU (-1.16 mmol·-1; 95%CL -1.80, -0.53). Plasma insulin was higher in GLU + GAL and GLU compared with GAL but not different between GLU + GAL and GLU. Plasma galactose concentration was higher in GAL compared with GLU (3.35 mmol·L-1; 95%CL 3.07, 3.63) and GAL + GLU (3.22 mmol·L-1; 95%CL 3.54, 2.90) with no difference between GLU + GAL (0.13 mmol·L-1; 95%CL -0.11, 0.37) and GLU. Compared with galactose or a galactose + glucose blend, glucose feeding was more effective in postexercise muscle glycogen synthesis. Comparable muscle glycogen synthesis was observed with galactose-glucose coingestion and exclusive galactose-only ingestion.NEW & NOTEWORTHY Postexercise galactose-glucose coingestion or exclusive galactose-only ingestion resulted in a lower rate of skeletal-muscle glycogen replenishment compared with exclusive glucose-only ingestion. Comparable muscle glycogen synthesis was observed with galactose-glucose coingestion and exclusive galactose-only ingestion.

Oxidation of independent and combined ingested galactose and glucose during exercise.

Coingestion of glucose and galactose has been shown to enhance splanchnic extraction and metabolism of ingested galactose at rest; effects during exercise are unknown. This study examined whether combined ingestion of galactose and glucose during exercise enhances exogenous galactose oxidation. Fourteen endurance-trained male and female participants [age, 27 (5) yr; V̇o2peak, 58.1 (7.0) mL·kg-1·min-1] performed cycle ergometry for 150 min at 50% peak power on four occasions, in a randomized counterbalanced manner. During exercise, they ingested beverages providing carbohydrates at rates of 0.4 g.min-1 galactose (GAL), 0.8 g.min-1 glucose (GLU), and on two occasions 0.8 g.min-1 total galactose-glucose (GAL + GLU; 1:1 ratio). Single-monosaccharide 13C-labeling (*) was used to calculate independent (GAL, GLU, GAL* + GLU, and GAL + GLU*) and combined (GAL* + GLU*, COMBINE) exogenous-monosaccharide oxidation between exercise. Plasma galactose concentrations with GAL + GLU [0.4 mmol.L; 95% confidence limits (CL): 0.1, 0.6] were lower (contrast: 0.5 mmol.L; 95% CL: 0.2, 0.8; P < 0.0001) than when GAL alone (0.9 mmol.L; 95% CL: 0.7, 1.2) was ingested. Exogenous carbohydrate oxidation with GAL alone (0.31 g·min-1; 95% CL: 0.28, 0.35) was marginally reduced (contrast: 0.05 g·min-1; 95% CL: -0.09, 0.00007; P = 0.01) when combined with glucose (GAL* + GLU 0.27 g·min-1; 0.24, 0.30). Total combined exogenous-carbohydrate oxidation (COMBINE: 0.57 g·min-1; 95% CL: 0.49, 0.64) was similar (contrast: 0.02 g·min-1; 95% CL: -0.05, 0.09; P = 0.63) when compared with isoenergetic GLU (0.55 g·min-1; 95% CL: 0.52, 0.58). In conclusion, coingestion of glucose and galactose did not enhance exogenous galactose oxidation during exercise. When combined, isoenergetic galactose-glucose ingestion elicited similar exogenous-carbohydrate oxidation to glucose suggesting galactose-glucose blends are a valid alternative for glucose as an exogenous-carbohydrate source during exercise.NEW & NOTEWORTHY Glucose and galactose coingestion blunted the galactosemia seen with galactose-only ingestion during exercise. Glucose and galactose coingestion did not enhance the oxidation of ingested galactose during exercise. Combined galactose-glucose (1:1 ratio) ingestion was oxidized to a similar extent as isoenergetic glucose-only ingestion during exercise. Galactose-glucose blends are a viable exogenous carbohydrate energy source for ingestion during exercise.

New Horizons in Carbohydrate Research and Application for Endurance Athletes.

The importance of carbohydrate as a fuel source for exercise and athletic performance is well established. Equally well developed are dietary carbohydrate intake guidelines for endurance athletes seeking to optimize their performance. This narrative review provides a contemporary perspective on research into the role of, and application of, carbohydrate in the diet of endurance athletes. The review discusses how recommendations could become increasingly refined and what future research would further our understanding of how to optimize dietary carbohydrate intake to positively impact endurance performance. High carbohydrate availability for prolonged intense exercise and competition performance remains a priority. Recent advances have been made on the recommended type and quantity of carbohydrates to be ingested before, during and after intense exercise bouts. Whilst reducing carbohydrate availability around selected exercise bouts to augment metabolic adaptations to training is now widely recommended, a contemporary view of the so-called train-low approach based on the totality of the current evidence suggests limited utility for enhancing performance benefits from training. Nonetheless, such studies have focused importance on periodizing carbohydrate intake based on, among other factors, the goal and demand of training or competition. This calls for a much more personalized approach to carbohydrate recommendations that could be further supported through future research and technological innovation (e.g., continuous glucose monitoring). Despite more than a century of investigations into carbohydrate nutrition, exercise metabolism and endurance performance, there are numerous new important discoveries, both from an applied and mechanistic perspective, on the horizon.

Addition of Fructose to a Carbohydrate-Rich Breakfast Improves Cycling Endurance Capacity in Trained Cyclists.

It was previously demonstrated that postexercise ingestion of fructose-glucose mixtures can lead to superior liver and equal muscle glycogen synthesis as compared with glucose-based carbohydrates (CHOs) only. After an overnight fast, liver glycogen stores are reduced, and based on this we hypothesized that addition of fructose to a glucose-based breakfast would lead to improved subsequent endurance exercise capacity. In this double-blind cross-over randomized study (eight males, peak oxygen uptake: 62.2 ± 5.4 ml·kg-1·min-1), participants completed two experimental trials consisting of two exercise bouts. In the afternoon of Day 1, they completed a cycling interval training session to normalize glycogen stores after which a standardized high-CHO diet was provided for 4 hr. On Day 2, in the morning, participants received 2 g/kg of CHOs in the form of glucose and rice or fructose and rice, both in a CHO ratio of 1:2. Two hours later they commenced cycling exercise session at the intensity of the first ventilatory threshold until task failure. Exercise capacity was higher in fructose and rice (137.0 ± 22.7 min) as compared with glucose and rice (130.06 ± 19.87 min; p = .046). Blood glucose and blood lactate did not differ between the trials (p > .05) and neither did CHO and fat oxidation rates (p > .05). However, due to the duration of exercise, total CHO oxidation was higher in fructose and rice (326 ± 60 g vs. 298 ± 61 g, p = .009). Present data demonstrate that addition of fructose to a glucose-based CHO source at breakfast improves endurance exercise capacity. Further studies are required to determine the mechanisms and optimal dose and ratio.

Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g h-1 versus 90 g h-1 at different ratios.

PURPOSE: This study aimed to investigate whether carbohydrate ingestion during 3 h long endurance exercise in highly trained cyclists at a rate of 120 g h-1 in 0.8:1 ratio between fructose and glucose-based carbohydrates would result in higher exogenous and lower endogenous carbohydrate oxidation rates as compared to ingestion of 90 g h-1 in 1:2 ratio, which is the currently recommended approach for exercise of this duration. METHODS: Eleven male participants (V̇O2peak 62.6 ± 7 mL kg-1 min-1, gas exchange threshold (GET) 270 ± 17 W and Respiratory compensation point 328 ± 32 W) completed the study involving 4 experimental visits consisting of 3 h cycling commencing after an overnight fast at an intensity equivalent to 95% GET. During the trials they received carbohydrates at an average rate of 120 or 90 g h-1 in 0.8:1 or 1:2 fructose-maltodextrin ratio, respectively. Carbohydrates were naturally high or low in 13C stable isotopes enabling subsequent calculations of exogenous and endogenous carbohydrate oxidation rates. RESULTS: Exogenous carbohydrate oxidation rates were higher in the 120 g h-1 condition (120-180 min: 1.51 ± 0.22 g min-1) as compared to the 90 g h-1 condition (1.29 ± 0.16 g min-1; p = 0.026). Endogenous carbohydrate oxidation rates did not differ between conditions (2.15 ± 0.30 and 2.20 ± 0.33 g min-1 for 120 and 90 g h-1 conditions, respectively; p = 0.786). CONCLUSIONS: The results suggest that carbohydrate ingestion at 120 g h-1 in 0.8:1 fructose-maltodextrin ratio as compared with 90 g h-1 in 1:2 ratio offers higher exogenous carbohydrate oxidation rates but no additional sparing of endogenous carbohydrates. Further studies should investigate potential performance effects of such carbohydrate ingestion strategies.

Power profiling and the power-duration relationship in cycling: a narrative review.

Emerging trends in technological innovations, data analysis and practical applications have facilitated the measurement of cycling power output in the field, leading to improvements in training prescription, performance testing and race analysis. This review aimed to critically reflect on power profiling strategies in association with the power-duration relationship in cycling, to provide an updated view for applied researchers and practitioners. The authors elaborate on measuring power output followed by an outline of the methodological approaches to power profiling. Moreover, the deriving a power-duration relationship section presents existing concepts of power-duration models alongside exercise intensity domains. Combining laboratory and field testing discusses how traditional laboratory and field testing can be combined to inform and individualize the power profiling approach. Deriving the parameters of power-duration modelling suggests how these measures can be obtained from laboratory and field testing, including criteria for ensuring a high ecological validity (e.g. rider specialization, race demands). It is recommended that field testing should always be conducted in accordance with pre-established guidelines from the existing literature (e.g. set number of prediction trials, inter-trial recovery, road gradient and data analysis). It is also recommended to avoid single effort prediction trials, such as functional threshold power. Power-duration parameter estimates can be derived from the 2 parameter linear or non-linear critical power model: P(t) = W'/t + CP (W'-work capacity above CP; t-time). Structured field testing should be included to obtain an accurate fingerprint of a cyclist's power profile.

Commercially available carbohydrate drink with menthol fails to improve thermal perception or cycling exercise capacity in males.

The purpose of this double-blinded, crossover randomized and counterbalanced study was to compare the effects of ingesting a tepid commercially available carbohydrate-menthol-containing sports drink (menthol) and an isocaloric carbohydrate-containing sports drink (placebo) on thermal perception and cycling endurance capacity "in a simulated home virtual cycling environment". It was hypothesized that the addition of menthol would improve indicators of thermal perception and improve endurance exercise capacity. Twelve healthy, endurance-trained males (age 29 ± 5 years, height 181 ± 6 cm, body mass 79 ± 2 kg and V̇O2max 57.3 ± 6.4 mL kg-1 min-1) completed two experimental trials on a stationary bicycle without external air flow. Each trial consisted of (1) cycling for 60 min at 90% of the first ventilatory threshold while receiving a fixed amount of menthol or placebo every 10 min followed immediately by (2) cycling until volitional exhaustion (TTE) at 105% of the intensity corresponding to the respiratory compensation point. TTE did not differ between both conditions (541 ± 177 and 566 ± 150 s for menthol and placebo; p > 0.05) and neither did ratings of perceived thermal comfort or thermal sensation (p > 0.05). Also, the rectal temperature at the end of TTE was comparable between menthol and placebo trials (38.7 ± 0.2°C and 38.7 ± 0.3°C, respectively; p > 0.05). The present results demonstrate that the addition of menthol to commercially available sports drink does not improve thermal comfort or endurance exercise capacity during ∼65 min of intense virtual cycling.Highlights Ingestion of a commercially available carbohydrate-menthol beverage at high exercise intensity and without air flow does not improve endurance exercise capacity.When ingested with carbohydrates, it appears that a combination of carbohydrates and menthol does not improve thermal discomfort caused by intense exercise and a lack of air flow.A menthol concentration higher than 0.01% might be required to induce the reduction in thermal discomfort when ingested in combination with carbohydrates.

Exogenous ketosis increases blood and muscle oxygenation but not performance during exercise in hypoxia.

Available evidence indicates that elevated blood ketones are associated with improved hypoxic tolerance in rodents. From this perspective, we hypothesized that exogenous ketosis by oral intake of the ketone ester (R)-3-hydroxybutyl (R)-3-hydroxybutyrate (KE) may induce beneficial physiological effects during prolonged exercise in acute hypoxia. As we recently demonstrated KE to deplete blood bicarbonate, which per se may alter the physiological response to hypoxia, we evaluated the effect of KE both in the presence and absence of bicarbonate intake (BIC). Fourteen highly trained male cyclists performed a simulated cycling race (RACE) consisting of 3-h intermittent cycling (IMT180') followed by a 15-min time-trial (TT15') and an all-out sprint at 175% of lactate threshold (SPRINT). During RACE, fraction of inspired oxygen ([Formula: see text]) was gradually decreased from 18.6% to 14.5%. Before and during RACE, participants received either 1) 75 g of ketone ester (KE), 2) 300 mg/kg body mass bicarbonate (BIC), 3) KE + BIC, or 4) a control drink in addition to 60 g of carbohydrates/h in a randomized, crossover design. KE counteracted the hypoxia-induced drop in blood ([Formula: see text]) and muscle oxygenation by ∼3%. In contrast, BIC decreased [Formula: see text] by ∼2% without impacting muscle oxygenation. Performance during TT15' and SPRINT were similar between all conditions. In conclusion, KE slightly elevated the degree of blood and muscle oxygenation during prolonged exercise in moderate hypoxia without impacting exercise performance. Our data warrant to further investigate the potential of exogenous ketosis to improve muscular and cerebral oxygenation status, and exercise tolerance in extreme hypoxia.

Reliability and Validity of the CORE Sensor to Assess Core Body Temperature during Cycling Exercise.

Monitoring core body temperature (Tc) during training and competitions, especially in a hot environment, can help enhance an athlete's performance, as well as lower the risk for heat stroke. Accordingly, a noninvasive sensor that allows reliable monitoring of Tc would be highly beneficial in this context. One such novel non-invasive sensor was recently introduced onto the market (CORE, greenTEG, Rümlang, Switzerland), but, to our knowledge, a validation study of this device has not yet been reported. Therefore, the purpose of this study was to evaluate the validity and reliability of the CORE sensor. In Study I, 12 males were subjected to a low-to-moderate heat load by performing, on two separate occasions several days apart, two identical 60-min bouts of steady-state cycling in the laboratory at 19 °C and 30% relative humidity. In Study II, 13 males were subjected to moderate-to-high heat load by performing 90 min of cycling in the laboratory at 31 °C and 39% relative humidity. In both cases the core body temperatures indicated by the CORE sensor were compared to the corresponding values obtained using a rectal sensor (Trec). The first major finding was that the reliability of the CORE sensor is acceptable, since the mean bias between the two identical trials of exercise (0.02 °C) was not statistically significant. However, under both levels of heat load, the body temperature indicated by the CORE sensor did not agree well with Trec, with approximately 50% of all paired measurements differing by more than the predefined threshold for validity of ≤0.3 °C. In conclusion, the results obtained do not support the manufacturer's claim that the CORE sensor provides a valid measure of core body temperature.

High rates of fat oxidation are maintained after the sleep low approach despite delayed carbohydrate feeding during exercise.

Training with low carbohydrate availability enhances endurance training adaptations but training volume may be compromised. We explored whole-body metabolism and performance with delayed carbohydrate feeding during exercise undertaken following acute sleep-low training. We hypothesised this strategy would not suppress fat oxidation and would maintain exercise performance. The study involved three experimental trials and included 9 men and 1 woman (⩒O2peak = 58.8 ± 5.5 mL kg-1 min-1). Each trial started in the afternoon with an exhaustive cycling protocol. The following morning 1-h of steady-state cycling (SS) was followed by a time trial (TT). Carbohydrates (CHO) were not ingested in recovery from exhaustive exercise or during next day exercise in the Placebo trial (PLA); CHO were not ingested during recovery but were fed (15 g every ∼15-min) from 30-min into SS and continued during the TT in the delayed feeding trial (DELAY); CHO were provided during recovery (1.2 g/kg/h for 7 h) and next day exercise (as in DELAY) in a third condition (CHO). Exercise metabolism was assessed using indirect calorimetry and blood sampling. Fat oxidation rates during SS were similar in PLA (0.83 ± 0.17 g/min) and DELAY (0.78 ± 0.14 g/min) (p > 0.05) and higher than CHO (0.57 ± 0.27 g/min) (p < 0.05). There were no significant differences in TT performance (49.1 ± 10.7, 43.4 ± 7.6, 41.0 ± 7.9 min in PLA, DELAY and CHO, respectively; p > 0.05). Delayed carbohydrate feeding could be a strategy to maintain high-fat oxidation rates typically associated with exercise undertaken after the sleep-low approach to training but the acute performance effects remain inconclusive.

Impact of Post-Exercise Fructose-Maltodextrin Ingestion on Subsequent Endurance Performance.

Background: Current sports nutrition guidelines recommend athletes ingest carbohydrates at 1.0-1.2 g·kg-1·h-1 to optimize repletion of muscle glycogen during short-term recovery from endurance exercise. However, they do not provide specific advice on monosaccharides (e.g., fructose or glucose) other than to ingest carbohydrates of moderate to high glycaemic index. Recent evidence suggests that combined ingestion of fructose and glucose in recovery leads to enhanced liver glycogen synthesis and that this translates into improvement of subsequent endurance capacity. Purpose: The purpose of the present study was to investigate whether consuming a combination of fructose and glucose as opposed to glucose alone during short-term recovery (i.e., 4 h) from exhaustive exercise would also improve subsequent pre-loaded cycle time trial (TT) performance. Methods: Eight participants (seven men, one woman; V ∙ O2peak: 56.8 ± 5.0 mLO2·min-1·kg-1; Wmax: 352 ± 41 W) participated in this randomized double-blind study. Each experimental session involved a glycogen reducing exercise bout in the morning, a 4-h recovery period and 1-h of steady state (SS) exercise at 50% Wmax followed by a ~40-min simulated TT. During recovery carbohydrates were ingested at a rate of 1.2 g·kg-1·h-1 in the form of fructose and maltodextrin (FRU + MD) or dextrose and maltodextrin (GLU + MD) (both in 1:1.5 ratio). Substrate oxidation rates, including ingested carbohydrate oxidation, were determined during the steady state (SS). Blood samples were collected during recovery, during the SS exercise and at the end of the TT for determination of glucose and lactate concentrations. Results: There were no differences in TT performance [37.41 ± 3.45 (GLU + MD); 37.96 ± 5.20 min (FRU + MD), p = 0.547]. During the first 45-min of SS oxidation of ingested carbohydrates was greater in FRU + MD (1.86 ± 0.41 g-1·min-1 and 1.51 ± 0.37 g-1·min-1 for FRU + MD and GLU + MD, respectively; time x condition interaction p = 0.003) and there was a trend toward higher overall carbohydrate oxidation rates in FRU + MD (2.50 ± 0.36 g-1·min-1 and 2.31 ± 0.37 g-1·min-1 for FRU + MD and GLU + MD, respectively; p = 0.08). However, at 60-min of SS, differences in substrate oxidation disappeared. Conclusion: Ingestion of combined fructose and glucose compared to glucose only during recovery from an exhaustive exercise bout increased the ingested carbohydrate oxidation rate during subsequent exercise. Under the conditions studied, subsequent TT performance was not improved with fructose-glucose.

Comparable Exogenous Carbohydrate Oxidation from Lactose or Sucrose during Exercise.

PURPOSE: Ingesting readily oxidized carbohydrates (CHO) such as sucrose during exercise can improve endurance performance. Whether lactose can be utilized as a fuel source during exercise is unknown. The purpose of this study was to investigate the metabolic response to lactose ingestion during exercise, compared with sucrose or water. METHODS: Eleven participants (age, 22 ± 4 yr; V[Combining Dot Above]O2peak, 50.9 ± 4.7 mL·min·kg) cycled at 50% Wmax for 150 min on five occasions. Participants ingested CHO beverages (lactose or sucrose; 48 g·h, 0.8 g·min) or water throughout exercise. Total substrate and exogenous CHO oxidation was estimated using indirect calorimetry and stable isotope techniques (naturally high C-abundance CHO ingestion). Naturally low C-abundance CHO trials were conducted to correct background shifts in breath CO2 production. Venous blood samples were taken to determine plasma glucose, lactate, and nonesterified fatty acid concentrations. RESULTS: Mean exogenous CHO oxidation rates were comparable with lactose (0.56 ± 0.19 g·min) and sucrose (0.61 ± 0.10 g·min; P = 0.49) ingestion. Endogenous CHO oxidation contributed less to energy expenditure in lactose (38% ± 14%) versus water (50% ± 11%, P = 0.01) and sucrose (50% ± 7%, P ≤ 0.05). Fat oxidation was higher in lactose (42% ± 8%) than in sucrose (28% ± 6%; P ≤ 0.01); CHO conditions were lower than water (50% ± 11%; P ≤ 0.05). Plasma glucose was higher in lactose and sucrose than in water (P ≤ 0.01); plasma lactate was higher in sucrose than in water (P ≤ 0.01); plasma nonesterified fatty acids were higher in water than in sucrose (P ≤ 0.01). CONCLUSIONS: Lactose and sucrose exhibited similar exogenous CHO oxidation rates during exercise at moderate ingestion rates. Compared with sucrose ingestion, lactose resulted in higher fat and lower endogenous CHO oxidation.

Postexercise Fructose-Maltodextrin Ingestion Enhances Subsequent Endurance Capacity.

PURPOSE: Restoring skeletal muscle and hepatic glycogen content during short-term (<6 h) recovery from prolonged exercise is pertinent for athletes seeking to maximize performance in repeated exercise bouts. Previous research suggests that coingestion of fructose-glucose carbohydrate sources augments hepatic and has equivalent effects on skeletal muscle glycogen storage during short-term recovery from prolonged exercise compared with isocaloric glucose ingestion. The aim of the present investigation was to determine whether this has a discernible effect on subsequent exercise capacity. METHODS: Eight trained endurance runners and triathletes performed two experimental trials in a single-blind, randomized, and counterbalanced crossover design. Trials involved treadmill running to exhaustion at 70% V˙O2max, a 4-h recovery with 90 g·h of glucose-maltodextrin (GLU + MAL) or fructose-maltodextrin (FRU + MAL) ingestion (1:1.5 ratio), and a second bout of treadmill running to exhaustion at 70% V˙O2max. RESULTS: Exercise capacity in bout 2 was significantly greater with FRU + MAL (81.4 ± 22.3 vs 61.4 ± 9.6 min, P = 0.02), a large magnitude effect (effect size = 1.84 ± 1.12, 32.4% ± 19.9%). Total carbohydrate oxidation rates were not significantly different during bout 1 or 2 between trials, although total carbohydrate oxidized in bout 2 was significantly greater with FRU + MAL (223 ± 66 vs 157 ± 26 g, P = 0.02). Ingested carbohydrate oxidation rates were greater during bout 2 with FRU + MAL (P = 0.001). Plasma glucose and nonesterified fatty acid concentrations were not significantly different between trials. Plasma lactate concentrations were significantly greater during recovery before bout 2 with FRU + MAL (P = 0.001). Self-reported nausea and stomach fullness during bout 2 were marginally in favor of FRU + MAL. CONCLUSION: Short-term recovery of endurance capacity was significantly enhanced with FRU + MAL versus GLU + MAL ingestion during recovery.