The effects of acute carbohydrate and caffeine feeding strategies on cycling efficiency

The effect of acute manipulation of carbohydrate availability on high intensity running performance, running economy, critical speed, and substrate metabolism in trained Male runners

Completing selected training sessions with reduced glycogen availability is associated with greater signalling and improved muscle oxidative capacity, although it may impact the overall quality of the session. We examined the effects of low carbohydrate availability on high intensity exercise performance, running economy, critical speed, and substrate metabolism. On two occasions, nine male runners (V̇O2peak 60.3 ± 3.3 mL.kg-1.min-1) completed a glycogen depletion protocol involving 90-min at 75%vV̇O2peak followed by 10 × 1-min at 110% vV̇O2peak. This was followed either by high (HIGH) or low (LOW) carbohydrate intake (>6 g.kg-1.day-1 and <50 g.day-1, respectively) until completion of a performance protocol on day 2 consisting of a series of time-trials (TT) (50m to 3000m) and physiological assessments. There were no differences between LOW and HIGH for any TT distance (mean TT performance times for LOW and HIGH were: 3000m TT 651.7 ± 52.8s and 646.4 ± 52.5s, 1500 m TT 304.0 ± 20.2s and 304.2 ± 22.1s, 400 m TT 67.64 ± 4.2s and 67.3 ± 3.8s, 50 m TT 7.27 ± 0.44s and 7.25 ± 0.45s, respectively, P > 0.05), though some athletes performed better in LOW (n = 5). While fat oxidation in LOW was significantly greater than HIGH (Δ0.32 ± 0.14 g.min-1; P < 0.001 at 14 km.h-1 and Δ0.34 ± 0.12 g.min-1 at 16 km.h-1; P < 0.01), running economy did not differ between trials (P > 0.05). Acute manipulation of carbohydrate availability showed immediate effects on substrate metabolism evidenced by greater fat oxidation without changes in RE. Acute low carbohydrate availability did not affect high intensity running performance across a range of distances.Highlights Acute manipulation of muscle glycogen availability using an exercise and dietary manipulation protocol did not affect subsequent high intensity running performance across a range of running distances.Reduced muscle glycogen resulted in a marked increase in fat oxidation in low glycogen condition but no changes in running economy or critical speed.Individual factors should be considered when prescribing high intensity sessions with restricted carbohydrate availability.

Carbohydrate intake before and during high intensity exercise with reduced muscle glycogen availability affects the speed of muscle reoxygenation and performance

Muscle glycogen state and carbohydrate (CHO) supplementation before and during exercise may impact responses to high-intensity interval training (HIIT). This study determined cardiorespiratory, substrate metabolism, muscle oxygenation, and performance when completing HIIT with or without CHO supplementation in a muscle glycogen depleted state. On two occasions, in a cross-over design, eight male cyclists performed a glycogen depletion protocol prior to HIIT during which either a 6% CHO drink (60 g.hr^-1) or placebo (%CHO, PLA) was consumed. HIIT consisted of 5 × 2 min at 80% peak power output (PPO), 3 × 10-min bouts of steady-state (SS) cycling (50, 55, 60% PPO), and a time-to-exhaustion (TTE) test. There was no difference in SS [Formula: see text], HR, substrate oxidation and gross efficiency (GE %) between CHO and PLA conditions. A faster rate of muscle reoxygenation (%. s^-1) existed in PLA after the 1st (Δ - 0.23 ± 0.22, d = 0.58, P < 0.05) and 3rd HIIT intervals (Δ - 0.34 ± 0.25, d = 1.02, P < 0.05). TTE was greater in CHO (7.1 ± 5.4 min) than PLA (2.5 ± 2.3 min, d = 0.98, P < 0.05). CHO consumption before and during exercise under reduced muscle glycogen conditions did not suppress fat oxidation, suggesting a strong regulatory role of muscle glycogen on substrate metabolism. However, CHO ingestion provided a performance benefit under intense exercise conditions commenced with reduced muscle glycogen. More research is needed to understand the significance of altered muscle oxygenation patterns during exercise.

Meta-Analysis of Carbohydrate Solution Intake during Prolonged Exercise in Adults: From the Last 45+ Years' Perspective

Carbohydrate (CHO) supplementation during prolonged exercise postpones fatigue. However, the optimum administration timing, dosage, type of CHO intake, and possible interaction of the ergogenic effect with athletes' cardiorespiratory fitness (CRF) are not clear. Ninety-six studies (from relevant databases based on predefined eligibility criteria) were selected for meta-analysis to investigate the acute effect of ≤20% CHO solutions on prolonged exercise performance. The between-subject standardized mean difference [SMD = ([mean post-value treatment group-mean post-value control group]/pooled variance)] was assessed. Overall, SMD [95% CI] of 0.43 [0.35, 0.51] was significant (p < 0.001). Subgroup analysis showed that SMD was reduced as the subjects' CRF level increased, with a 6-8% CHO solution composed of GL:FRU improving performance (exercise: 1-4 h); administration during the event led to a superior performance compared to administration before the exercise, with a 6-8% single-source CHO solution increasing performance in intermittent and 'stop and start' sports and an ~6% CHO solution appearing beneficial for 45-60 min exercises, but there were no significant differences between subjects' gender and age groups, varied CHO concentrations, doses, or types in the effect measurement. The evidence found was sound enough to support the hypothesis that CHO solutions, when ingested during endurance exercise, have ergogenic action and a possible crossover interaction with the subject's CRF.

Effect of Carbohydrate Content in a Pre-event Meal on Endurance Performance-Determining Factors: A Randomized Controlled Crossover-Trial

The current study aimed to investigate the effect of the relative CHO content in a pre-event meal on time to exhaustion (TTE), peak oxygen uptake (V∙O2peak), the 2nd lactate threshold (LT2), onset of blood lactate accumulation (OBLA), and work economy (WE) and to compare responses between well-trained and recreationally trained individuals. Eleven well-trained and 10 recreationally trained men performed three trials in a randomized cross-over design, in which they performed exercise tests (1) after a high-CHO pre-event meal (3 g · kg⁻¹), (2) a low-CHO pre-event meal (0.5 g · kg⁻¹), or (3) in a fasted-state. The test protocol consisted of five submaximal 5-min constant-velocity bouts of increasing intensity and a graded exercise test (GXT) to measure TTE. A repeated measure ANOVA with a between-subjects factor (well-trained vs. recreational) was performed. A main effect of pre-event meal was found (p = 0.001), with TTE being 8.0% longer following the high-CHO meal compared to the fasted state (p = 0.009) and 7.2% longer compared to the low-CHO meal (p = 0.010). No significant effect of pre-event meal on V∙O2peak, LT2, OBLA, or WE (p ≥ 0.087) was found and no significant interaction effect between training status and pre-event CHO intake was found for TTE or any of the performance-determining variables (p ≥ 0.257). In conclusion, high-CHO content in the pre-event meal led to a longer TTE compared to a meal with a low-CHO content or exercising in a fasted state, both in well-trained and recreationally trained participants. However, the underlying physiological reason for the increased TTE is unclear, as no effect of pre-event meal on the main physiological performance-determining variables was found. Thus, pre-event CHO intake should be standardized when the goal is to assess endurance performance but seems to be of less importance when assessing the main performance-determining variables.

Carbohydrate supplementation during a simulated 10-km open water swimming race: effects on physiological, perceptual parameters and performance

The aim of the present study was to test the effect of carbohydrate ingestion, simulating a 10-km open water race competition on energy cost (Csw), perceived exertion (RPE), heart rate (HR), stroke rate (SR) and performance. We hypothesized that carbohydrate ingestion would reduce Csw and RPE in elite open water swimmers (OW-swimmers) and improve performance. Eight elite OW-swimmers swam for 3 × 30 min with 20-s of interval necessary to collect data in the swimming flume at a pre-set pace corresponding to their 10-km race pace, followed by a time to exhaustion test (TTE) at 100% of the peak oxygen uptake (V̇O_2peak). During the set, OW-swimmers ingested 45-g of carbohydrates (CHO) in 550-mL of water (8% solution) during each of the two intervals or a placebo solution (PLA). HR, RPE, V̇O₂ and SR were measured. Shapiro-Wilk test was used to verify the normal distribution of data. Two-way repeated measures ANOVA and t-test was performed (p < 0.05). A significant difference emerged in TTE between the trials (169.00 ± 91.06 s in CHO; 102.31 ± 57.47 s in PLA). HR, RPE and SR increased during the TTE but did not differ between trials. Csw did not show a significant main effect between the two conditions and in time course in both conditions. CHO ingestion significantly increased TTE at 100% of V̇O_2peak after 90-min of swimming at 10-km race pace. These findings indicate that CHO intake during a 10-km open water swimming competition should have a beneficial impact on performance in the final part of the race.

Physiological Response to Cycling With Variable Versus Constant Power Output

Introduction: Variable power output (VP) is one of the main characteristics of a road cycling mass-start. Tolerating VP during outdoor road cycling highly influences performance. There is a lack of continuous and comprehensive measurements during this power condition. Accordingly, the aim of the present study was to investigate physiological response to VP vs. constant power output (CP) as well as the perceived exertion of these two power conditions, and to investigate if variations in power output which span above lactate threshold (LT), differ from variations below LT.

Methods: 15 elite competitive cyclists completed three test days, including 1 day of baseline testing and 2 days of main testing, consisting of four bouts of 28 min at two different intensities, “low” at 70% of LT and “high” at 95% of LT, with VP and CP. VP was performed with a 15% fluctuation of the average power output every second minute. Maximal oxygen uptake (VO₂), respiratory exchange ratio (RER), heart rate (HR), blood lactate (LA), rating of perceived exertion (RPE), cadence (RPM) and power output (W) were measured.

Results: At both low and high intensity, the VP condition induced a significantly higher VO₂, HR and LA than the CP condition. Whole-bout RPE was similar between power conditions at high intensity. Additionally, at the high intensity, cycling with VP led to a greater increase in LA and lesser increase in RPE compared to cycling with CP.

Discussion: The results of this study show that, despite considerable differences in the demand during the VP and CP bouts, there are minor differences in the perceptual and physiological response directly following these two power conditions in a cohort of elite competitive cyclists. A practical implication of these findings is that training with VP seems to be a viable alternative to training with CP, at least at high intensity.

Partial Replacement of Maltodextrin by Sweet Potato Flour (Ipomoea Batatas L. Lamarck) in the Development of a Shake Beverage

Sweet potato flour contains low-glycemic complex carbohydrates and, when it is ingested, prevents insulin spikes and prolongs the feeling of satiety. The aim of this study was to elaborate and to verify the acceptability of the shake with the total or partial substitution of maltodextrin for sweet potato flour. To elaborate the shake beverage, we used a 22 factorial design, with three central points, thus generating seven formulations. For the taste, color, texture, appearance, acceptance and attitude of purchase properties, sensory tests were conducted using a nine-point hedonic scale and panelists (n = 50). The highest acceptability formulations, formulations 3 (10% sweet potato flour; 25% maltodextrin) and 7 (0% sweet potato flour; 25% maltodextrin), were submitted to pH, moisture, ash, protein, lipid, crude fiber and total carbohydrate analyses. The statistical difference between the formulations from the T test (p < 0.05) was verified for the moisture, ash and lipid parameters. Formulation 3 presented higher values of moisture (93.26 ± 0.57) and lipids (1.91 ± 0.01), and formulation 7 had higher values of ash (0.39 ± 0.01). The results of the sensorial and physicochemical analyses of the shake indicate that sweet potato flour shows potential for the elaboration of this drink.