CHO Oxidation Rates Research Articles

The Effect of Exercise Intensity on Carbohydrate Sparing Postexercise: Implications for Postexercise Hypoglycemia.

The purpose of this study was to determine the effect of exercise intensity on the proportion and rate of carbohydrate oxidation and glucoregulatory hormone responses during recovery from exercise. Six physically active participants completed 1hr of low-intensity (LI; 50% lactate threshold) or moderate-intensity (MI; 100% lactate threshold) exercise on separate days following a randomized counterbalanced design. During exercise and for 6hr of recovery, samples of expired air were collected to determine oxygen consumption, respiratory exchange ratio, energy expenditure, and substrate oxidation rates. Blood samples were also collected to measure glucoregulatory hormones (catecholamines, GH) and metabolites (glucose, free fatty acids, lactate, pH, and bicarbonate). During exercise, respiratory exchange ratio, energy expenditure, and the proportion and rate of carbohydrate (CHO) oxidation were higher during MI compared with LI. However, during recovery from MI, respiratory exchange ratio and the proportion and rate of CHO oxidation were lower than preexercise levels and corresponding LI. During exercise and early recovery, catecholamines and growth hormone were higher in MI than LI, and there was a trend for higher levels of free fatty acids in the early recovery from MI compared with LI. In summary, CHO oxidation during exercise increases with exercise intensity but there is a preference for CHO sparing (and fat oxidation) during recovery from MI exercise compared with LI exercise. This exercise intensity-dependent shift in substrate oxidation during recovery is explained, in part, by the pattern of change of key glucoregulatory hormones including catecholamines and growth hormone and plasma fatty acid concentrations.

Assessing exogenous carbohydrate intake needed to optimize human endurance performance across sex: insights from modeling runners pursuing a sub-2-h marathon.

Carbohydrate (CHO) availability sustains high metabolic demands during prolonged exercise. The adequacy of current CHO intake recommendations, 30-90 g·h-1 dependent on CHO mixture and tolerability, to support elite marathon performance is unclear. We sought to scrutinize the current upper limit recommendation for exogenous CHO intake to support modeled sub-2-h marathon (S2M) attempts across elite male and female runners. Male and female runners (n = 120 each) were modeled from published literature with reference characteristics necessary to complete a S2M (e.g., body mass and running economy). Completion of a S2M was considered across a range of respiratory exchange rates, with maximal starting skeletal muscle and liver glycogen content predicted for elite male and female runners. Modeled exogenous CHO bioavailability needed for male and female runners were 93 ± 26 and 108 ± 22 g·h-1, respectively (P < 0.0001, d = 0.61). Without exogenous CHO, males were modeled to deplete glycogen in 84 ± 7 min, females in 71 ± 5 min (P < 0.0001, d = 2.21) despite higher estimated CHO oxidation rates in males (5.1 ± 0.5 g·h-1) than females (4.4 ± 0.5 g·h-1; P < 0.0001, d = 1.47). Exogenous CHO intakes ≤ 90 g·h-1 are insufficient for 65% of modeled runners attempting a S2M. Current recommendations to support marathon performance appear inadequate for elite marathon runners but may be more suitable for male runners in pursuit of a S2M (56 of 120) than female runners (28 of 120).NEW & NOTEWORTHY This study scrutinizes the upper limit of exogenous carbohydrate (CHO) recommendations for elite male and female marathoners by modeling sex-specific needs across an extreme metabolic challenge lasting ∼2 h, a sub-2-h marathon. Contemporary nutritional guidelines to optimize marathon performance appear inadequate for most elite marathon runners but appear more appropriate for males over their female counterparts. Future research examining possible benefits of exogenous CHO intakes > 90 g·h-1 should prioritize female athlete study inclusion.

Pre-exercise isomaltulose intake affects carbohydrate oxidation reduction during endurance exercise and maximal power output in the subsequent Wingate test

BackgroundIngestion of low-glycemic index (GI) isomaltulose (ISO) not only suppresses subsequent carbohydrate (CHO) oxidation but also inversely retains more CHO after prolonged endurance exercise. Therefore, ISO intake may affect anaerobic power output after prolonged endurance exercise. This study aimed to clarify the time course of CHO utilization during endurance exercise after a single intake of ISO or sucrose (SUC) and the anaerobic power output at the end of endurance exercise.MethodsAfter an intake of either ISO or SUC, 13 athletes were kept at rest for 60 min. Thereafter, they performed a 90-min of treadmill running at their individual target level of % {rm{dot V}}{{rm{O}}_2}max. During the experimental session, the expired gas was recorded, and the energy expenditure (EE) and CHO oxidation rate were estimated. Immediately after 90 min of running, a 30-s Wingate test was performed, and the maximal anaerobic power output was compared between the ISO and SUC conditions.ResultsThe percentage of CHO-derived EE increased rapidly after CHO intake and then decreased gradually throughout the experiment. The slopes of the regression lines calculated from the time course in the CHO-derived EE were significantly (negatively) larger in the SUC condition (-19.4 ± 9.6 [%/h]) than in the ISO condition (-13.3 ± 7.5 [%/h]). Furthermore, the maximal power output in the Wingate test immediately after the endurance exercise was significantly higher in the ISO condition than in the SUC condition (peak power: 12.0 ± 0.6 vs. 11.5 ± 0.9 [W/kg]).ConclusionCompared with SUC intake, ISO intake does not produce an abrupt decline in the percentage of CHO-derived EE during prolonged endurance exercise; it remains relatively high until the final exercise phase. Additionally, anaerobic power output at the end of the exercise, largely contributed by anaerobic glycolysis, was greater after ISO intake than after SUC intake.

13C-glucose-fructose labeling reveals comparable exogenous CHO oxidation during exercise when consuming 120 g/h in fluid, gel, jelly chew, or coingestion

We examined the effects of carbohydrate (CHO) delivery form on exogenous CHO oxidation, gastrointestinal discomfort, and exercise capacity. In a randomized repeated-measures design [after 24 h of high CHO intake (8 g·kg-1) and preexercise meal (2 g·kg-1)], nine trained males ingested 120 g CHO·h-1 from fluid (DRINK), semisolid gel (GEL), solid jelly chew (CHEW), or a coingestion approach (MIX). Participants cycled for 180 min at 95% lactate threshold, followed by an exercise capacity test (150% lactate threshold). Peak rates of exogenous CHO oxidation (DRINK 1.56 ± 0.16, GEL 1.58 ± 0.13, CHEW 1.59 ± 0.08, MIX 1.66 ± 0.02 g·min-1) and oxidation efficiency (DRINK 72 ± 8%, GEL 72 ± 5%, CHEW 75 ± 5%, MIX, 75 ± 6%) were not different between trials (all P > 0.05). Despite ingesting 120 g·h-1, participants reported minimal symptoms of gastrointestinal distress across all trials. Exercise capacity was also not significantly different (all P > 0.05) between conditions (DRINK 446 ± 350, GEL 529 ± 396, CHEW 596 ± 416, MIX 469 ± 395 s). Data represent the first time that rates of exogenous CHO oxidation (via stable isotope methodology) have been simultaneously assessed with feeding strategies (i.e., preexercise CHO feeding and the different forms and combinations of CHO during exercise) commonly adopted by elite endurance athletes. We conclude that 120 g·h-1 CHO (in a 1:0.8 ratio of maltodextrin or glucose to fructose) is a practically tolerable strategy to promote high CHO availability and oxidation during exercise.NEW & NOTEWORTHY We demonstrate comparable rates of exogenous CHO oxidation from fluid, semisolid, solid, or a combination of sources. Considering the sustained high rates of total and exogenous CHO oxidation and relative lack of gastrointestinal symptoms, consuming 120 g CHO·h-1 appears to be a well-tolerated strategy to promote high CHO availability during exercise. Additionally, this is the first time that rates of exogenous CHO oxidation have been assessed with feeding strategies (e.g., coingestion of multiple CHO forms) typically reported by endurance athletes.

Impact of slow versus rapid digesting carbohydrates on substrate oxidation in pre-pubertal children: A randomized crossover trial

Consumption of rapid digesting sugars by children are under increased scrutiny because of their contribution to unhealthy weight gain. Previous studies in adults and children have suggested that altering the blend of carbohydrates (CHOs) consumed may cause shifts in substrate utilization. The purpose of this study was to examine the effects of consuming a slow digesting carbohydrate (SDC) and rapid digesting carbohydrate (RDC) on CHO and fat oxidation, glucose, and insulin responses at rest, during exercise, and post-exercise rest in pre-pubescent children. A randomized, double-blind, crossover design was used. Nineteen pre-pubescent children (n=10 boys, n=9 girls, mean±standard error, age=9.84±0.37-yrs) participated. Visits to the laboratory began with a 30-min measurement of resting metabolism followed by consumption of either an RDC or SDC drink. Postprandial resting metabolism was recorded for 60-min, immediately followed by 60-min of submaximal cycling exercise while metabolism was recorded, which was immediately followed by another 60-min recording of post-exercise metabolism. Total CHO and fat oxidation, endogenous and exogenous CHO oxidation, blood glucose, and insulin were assessed. Total CHO oxidation rate (g∙min-1) was greater after the RDC drink at 60min (p=0.032). Endogenous CHO oxidation rate (g∙min-1) was greater after the SDC drink at 15min (p≤0.010). Cumulative endogenous CHO oxidation (g) was greater after the SDC drink at 45min (p=0.009). Endogenous CHO oxidation accounted for a greater proportion of substrate oxidation after the first 60-min rest period (p=0.028), while exogenous CHO oxidation accounted for a greater proportion of substrate oxidation for the RDC at all time points (p≤0.019). The present study provides novel data suggesting that an SDC promotes greater endogenous substrate utilization in pre-pubertal children, which may have beneficial health impacts on energy intake and carbohydrate regulation/metabolism during growth and development. NCT03185884, clinicaltrials.gov.

Sustained Exposure to High Carbohydrate Availability Does Not Influence Iron-Regulatory Responses in Elite Endurance Athletes.

This study implemented a 2-week high carbohydrate (CHO) diet intended to maximize CHO oxidation rates and examined the iron-regulatory response to a 26-km race walking effort. Twenty international-level, male race walkers were assigned to either a novel high CHO diet (MAX = 10g/kg body mass CHO daily) inclusive of gut-training strategies, or a moderate CHO control diet (CON = 6g/kg body mass CHO daily) for a 2-week training period. The athletes completed a 26-km race walking test protocol before and after the dietary intervention. Venous blood samples were collected pre-, post-, and 3hr postexercise and measured for serum ferritin, interleukin-6, and hepcidin-25 concentrations. Similar decreases in serum ferritin (17-23%) occurred postintervention in MAX and CON. At the baseline, CON had a greater postexercise increase in interleukin-6 levels after 26km of walking (20.1-fold, 95% CI [9.2, 35.7]) compared with MAX (10.2-fold, 95% CI [3.7, 18.7]). A similar finding was evident for hepcidin levels 3hr postexercise (CON = 10.8-fold, 95% CI [4.8, 21.2]; MAX = 8.8-fold, 95% CI [3.9, 16.4]). Postintervention, there were no substantial differences in the interleukin-6 response (CON = 13.6-fold, 95% CI [9.2, 20.5]; MAX = 11.2-fold, 95% CI [6.5, 21.3]) or hepcidin levels (CON = 7.1-fold, 95% CI [2.1, 15.4]; MAX = 6.3-fold, 95% CI [1.8, 14.6]) between the dietary groups. Higher resting serum ferritin (p = .004) and hotter trial ambient temperatures (p = .014) were associated with greater hepcidin levels 3hr postexercise. Very high CHO diets employed by endurance athletes to increase CHO oxidation have little impact on iron regulation in elite athletes. It appears that variations in serum ferritin concentration and ambient temperature, rather than dietary CHO, are associated with increased hepcidin concentrations 3hr postexercise.

Metabolic, hormonal and performance effects of isomaltulose ingestion before prolonged aerobic exercise: a double-blind, randomised, cross-over trial

BackgroundIsomaltulose has been discussed as a low glycaemic carbohydrate but evidence concerning performance benefits and physiological responses has produced varying results. Therefore, we primarily aimed to investigate the effects of isomaltulose ingestion compared to glucose and maltodextrin on fat and carbohydrate oxidation rates, blood glucose levels and serum hormone concentrations of insulin and glucose-dependent insulinotropic polypeptide (GIP). As secondary aims, we assessed running performance and gastrointestinal discomfort.MethodsTwenty-one male recreational endurance runners performed a 70-min constant load trial at 70% maximal running speed (Vmax), followed by a time to exhaustion (TTE) test at 85% Vmax after ingesting either 50 g isomaltulose, maltodextrin or glucose. Fat and carbohydrate oxidation rates were calculated from spiroergometric data. Venous blood samples for measurement of GIP and insulin were drawn before, after the constant load trial and after the TTE. Capillary blood samples for glucose concentrations and subjective feeling of gastrointestinal discomfort were collected every 10 min during the constant load trial.ResultsNo between-condition differences were observed in the area under the curve analysis of fat (p = 0.576) and carbohydrate oxidation rates (p = 0.887). Isomaltulose ingestion led to lower baseline postprandial concentrations of blood glucose compared to maltodextrin (percent change [95% confidence interval], − 16.7% [− 21.8,-11.6], p < 0.001) and glucose (− 11.5% [− 17.3,-5.7], p = 0.001). Similarly, insulin and GIP concentrations were also lower following isomaltulose ingestion compared to maltodextrin (− 40.3% [− 50.5,-30.0], p = 0.001 and − 69.1% [− 74.3,-63.8], p < 0.001, respectively) and glucose (− 32.6% [− 43.9,-21.2], p = 0.012 and − 55.8% [− 70.7,-40.9], p < 0.001, respectively). Furthermore, glucose fluctuation was lower after isomaltulose ingestion compared to maltodextrin (− 26.0% [− 34.2,-17.8], p < 0.001) and glucose (− 17.4% [− 29.1,-5.6], p < 0.001). However, during and after exercise, no between-condition differences for glucose (p = 0.872), insulin (p = 0.503) and GIP (p = 0.244) were observed. No between-condition differences were found for TTE (p = 0.876) or gastrointestinal discomfort (p = 0.119).ConclusionIsomaltulose ingestion led to lower baseline postprandial concentrations of glucose, insulin and GIP compared to maltodextrin and glucose. Consequently, blood glucose fluctuations were lower during treadmill running after isomaltulose ingestion, while no between-condition differences were observed for CHO and fat oxidation rates, treadmill running performance and gastrointestinal discomfort. Further research is required to provide specific guidelines on supplementing isomaltulose in performance and health settings.

Substrate oxidation during exercise in taekwondo athletes: impact of aerobic fitness status

The present study aimed to investigate the potential effect of different aerobic fitness levels on substrate oxidation in trained taekwondo athletes. 57 male athletes (age 21.10±7.79 years; VO2max 50.67±6.67 ml/kg/min) with regular weekly taekwondo training and training experience of at least three years completed a graded exercise test to exhaustion on a treadmill. Maximal fat oxidation (MFO), the exercise intensity related to MFO (Fatmax), and carbohydrate (CHO) oxidation rate were measured using indirect calorimetry methods. The athletes then were divided into a low (&lt;50 ml/kg/min, n=18) and high (&gt;50 ml/kg/min, n=39) VO2max group. The average MFO was higher in the high VO2max group than in the low VO2max group (0.46±0.19 vs 0.28±0.11 g/min; P&lt;0.001). Although Fatmax tended toward higher values in the high VO2max group, no difference was observed between the groups (49.15±15.22 vs 42.42±12.37% of VO2max; P=0.18). It was also shown that the high VO2max group had a lower CHO oxidation rate and a higher fat oxidation rate at given exercise intensities. In conclusion, it seems that MFO and substrate oxidation rates in taekwondo athletes can be influenced by aerobic fitness level such that the athletes with higher VO2max appeared to use more fat as a fuel source for energy supply during a given exercise.

Adaptation to a low carbohydrate high fat diet is rapid but impairs endurance exercise metabolism and performance despite enhanced glycogen availability.

Key points Brief (5–6 days) adaptation to a low carbohydrate high fat diet in elite athletes increased exercise fat oxidation to rates previously observed with medium (3–4 weeks) or chronic (>12 months) adherence to this diet, with metabolic changes being washed out in a similar time frame.Increased fat utilisation during exercise was associated with a 5–8% increase in oxygen cost at speeds related to Olympic Programme races.Acute restoration of endogenous carbohydrate (CHO) availability (24 h high CHO diet, pre‐race CHO) only partially restored substrate utilisation during a race warm‐up. Fat oxidation continued to be elevated above baseline values although it was lower than achieved by 5–6 days’ keto adaptation; CHO oxidation only reached 61% and 78% of values previously seen at exercise intensities related to race events.Acute restoration of CHO availability failed to overturn the impairment of high‐intensity endurance performance previously associated with low carbohydrate high fat adaptation, potentially due to the blunted capacity for CHO oxidation. We investigated substrate utilisation during exercise after brief (5–6 days) adaptation to a ketogenic low‐carbohydrate (CHO), high‐fat (LCHF) diet and similar washout period. Thirteen world‐class male race walkers completed economy testing, 25 km training and a 10,000 m race (Baseline), with high CHO availability (HCHO), repeating this (Adaptation) after 5–6 days’ LCHF (n = 7; CHO: <50 g day−1, protein: 2.2 g kg−1 day−1; 80% fat) or HCHO (n = 6; CHO: 9.7 g kg−1 day−1; protein: 2.2 g kg−1 day−1) diet. An Adaptation race was undertaken after 24 h HCHO and pre‐race CHO (2 g kg−1) diet, identical to the Baseline race. Substantial (>200%) increases in exercise fat oxidation occurred in the LCHF Adaptation economy and 25 km tests, reaching mean rates of ∼1.43 g min−1. However, relative V˙O2 (ml min−1 kg−1) was higher (P < 0.0001), by ∼8% and 5% at speeds related to 50 km and 20 km events. During Adaptation race warm‐up in the LCHF group, rates of fat and CHO oxidation at these speeds were decreased and increased, respectively (P < 0.001), compared with the previous day, but were not restored to Baseline values. Performance changes differed between groups (P = 0.009), with all HCHO athletes improving in the Adaptation race (5.7 (5.6)%), while 6/7 LCHF athletes were slower (2.2 (3.4)%). Substrate utilisation returned to Baseline values after 5–6 days of HCHO diet. In summary, robust changes in exercise substrate use occurred in 5–6 days of extreme changes in CHO intake. However, adaptation to a LCHF diet plus acute restoration of endogenous CHO availability failed to restore high‐intensity endurance performance, with CHO oxidation rates remaining blunted.

Carbohydrate Hydrogel Products Do Not Improve Performance or Gastrointestinal Distress During Moderate-Intensity Endurance Exercise.

The benefits of ingesting exogenous carbohydrate (CHO) during prolonged exercise performance are well established. A recent food technology innovation has seen sodium alginate and pectin included in solutions of multiple transportable CHO, to encapsulate them at pH levels found in the stomach. Marketing claims include enhanced gastric emptying and delivery of CHO to the muscle with less gastrointestinal distress, leading to better sports performance. Emerging literature around such claims was identified by searching electronic databases; inclusion criteria were randomized controlled trials investigating metabolic and/or exercise performance parameters during endurance exercise >1hr, with CHO hydrogels versus traditional CHO fluids and/or noncaloric hydrogels. Limitations associated with the heterogeneity of exercise protocols and control comparisons are noted. To date, improvements in exercise performance/capacity have not been clearly demonstrated with ingestion of CHO hydrogels above traditional CHO fluids. Studies utilizing isotopic tracers demonstrate similar rates of exogenous CHO oxidation, and subjective ratings of gastrointestinal distress do not appear to be different. Overall, data do not support any metabolic or performance advantages to exogenous CHO delivery in hydrogel form over traditional CHO preparations; although, one study demonstrates a possible glycogen sparing effect. The authors note that the current literature has largely failed to investigate the conditions under which maximal CHO availability is needed; high-performance athletes undertaking prolonged events at high relative and absolute exercise intensities. Although investigations are needed to better target the testimonials provided about CHO hydrogels, current evidence suggests that they are similar in outcome and a benefit to traditional CHO sources.

Comparable Exogenous Carbohydrate Oxidation With Lactose Or Sucrose Feeding During Endurance Exercise

PURPOSE: Endogenous carbohydrate (CHO) availability can limit endurance exercise performance. CHO ingested during exercise such as glucose, glucose polymers and sucrose are readily oxidized and can improve endurance performance. The extent to which lactose can be utilized as a fuel source during exercise is unknown. The purpose is to elucidate the metabolic response to lactose ingestion during endurance exercise, compared to sucrose or water. METHODS: 11 participants (mean ± SD: 22 ± 4 years, 50.9 ± 4.7 ml.min-1.kg-1) cycled for 150 min at 50% of Wmax on 3 occasions. During exercise participants ingested, in a randomized order, water (WAT), lactose (LAC) or sucrose (SUC) containing beverages; a CHO dose of 0.8 g.min-1 (48 g.h-1) was used. Indirect calorimetry was used to calculate fat and total CHO oxidation and stable isotope tracer methodology (natural high 13C abundance CHO ingestion, 13C:12C ratio determination in expired breath by isotope-ratio mass spectrometry) was used to quantify exogenous CHO oxidation. Venous blood samples were taken throughout exercise and analyzed for glucose, lactate and non-esterified fatty acids (NEFA). RESULTS: Mean exogenous CHO oxidation rates in LAC (0.55 ± 0.19 g.min-1) and SUC (0.58 ± 0.10 g.min-1) were similar (P=0.68). Endogenous CHO oxidation contributed less to energy expenditure (EE) in LAC (39 ± 14 %) than in WAT (50 ± 11 %, P=0.01) and SUC (50 ± 8 %, P=0.04). Fat oxidation contributed most to EE in WAT (50 ± 11 %), which was significantly greater than in LAC (42 ± 8 %, P=0.04) and SUC (28 ± 6 %, P<0.01), with fat oxidation higher in LAC than SUC (P<0.01). Plasma glucose was significantly higher in LAC (5.2 ± 0.4 mmol.L-1) and SUC (5.3 ± 0.5 mmol.L-1) than WAT (4.6 ± 0.5 mmol.L-1, P≤0.01). Plasma lactate was significantly higher in SUC (1.7 ± 0.5 mmol.L-1) than WAT (1.5 ± 0.4 mmol.L-1, P<0.01). Plasma NEFA were significantly higher in WAT (1.1 ± 0.4 mmol.L-1) than SUC (0.5 ± 0.3 mmol.L-1, P<0.01), and tended to be higher in WAT than LAC (0.7 ± 0.4 mmol.L-1, P=0.08). CONCLUSIONS: Exogenous CHO oxidation during exercise was comparable from ingested lactose and sucrose. However, lactose ingestion promoted higher fat and lower endogenous CHO oxidation during exercise than sucrose. This suggests that lactose may be at least as efficacious as commonly used CHO sources for improving exercise performance.

Does Exercise Intensity Influence Dietary Protein Requirements Of Male Endurance Athletes?

Adequate protein intake is important for endurance athletes to replenish exercise-induced amino acid (AA) oxidation and support post-exercise muscle and whole body protein synthesis. High-intensity endurance exercise is associated with increased carbohydrate oxidation during exercise and greater protein turnover (synthesis and breakdown) after exercise relative to lower intensity exercise. Muscle glycogen depletion can increase AA oxidation during exercise and increase daily protein requirements. PURPOSE: To determine the impact of exercise intensity during prolonged endurance exercise on estimates of dietary protein requirements in endurance athletes. METHODS: Eight males (26±3y, 76±16kg; 62±6 ml O2·kg-1· min-1; mean±SD) completed two trials in a randomized order with exercise (20-km run) performed at a low (LOW; 72±1% HRmax, 55±5% VO2peak) or high (HIGH; 88±1%HRmax, 75±7% VO2peak) intensity. After 2 days of exercise and dietary (1.4g·kg-1·d-1 protein) control, participants consumed 0.6g·kg-1 CHO before a 20-km treadmill run with continuous HR monitoring and periodic measurement of gas exchange (indirect calorimetry). During the 8h post-exercise recovery period, participants consumed 8.6g·kg-1·d-1 CHO and hourly meals providing 0.93g ·kg-1·d-1 protein as crystalline AA modeled after egg protein, which was enriched with [13C]phenylalanine as an indicator AA. Breath and urine were collected at isotopic and metabolic steady state to determine phenylalanine excretion (F13CO2), flux (Q; estimate of protein breakdown), and oxidation (OX; reciprocal of protein synthesis). RESULTS: Preliminary analysis (n=6) showed that respiratory exchange ratio during exercise was higher in HIGH vs. LOW (0.92±0.03 vs. 0.88±0.03, p<0.05), which corresponded to a 37% greater CHO oxidation rate in HIGH (3.12±0.76 vs. 1.96±0.52 g·min-1, p<0.01). Exercise duration was shorter in HIGH vs LOW (86±18 vs. 112±23 min, p<0.01). F13CO2 was not different between trials (HIGH: 0.94±0.25 vs. LOW: 0.89±0.14 umol·kg-1·h-1, p>0.05). Urinary analysis is ongoing to determine Q and OX. CONCLUSION: Preliminary findings suggest that prolonged, high-intensity endurance exercise increases CHO oxidation during exercise but has little impact on estimates of protein requirements of male endurance athletes.

Comparable Exogenous Carbohydrate Oxidation from Lactose or Sucrose during Exercise.

ABSTRACTPurposeIngesting 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.MethodsEleven participants (age, 22 ± 4 yr; V̇O2peak, 50.9 ± 4.7 mL·min−1·kg−1) cycled at 50% Wmax for 150 min on five occasions. Participants ingested CHO beverages (lactose or sucrose; 48 g·h−1, 0.8 g·min−1) or water throughout exercise. Total substrate and exogenous CHO oxidation was estimated using indirect calorimetry and stable isotope techniques (naturally high 13C-abundance CHO ingestion). Naturally low 13C-abundance CHO trials were conducted to correct background shifts in breath 13CO2 production. Venous blood samples were taken to determine plasma glucose, lactate, and nonesterified fatty acid concentrations.ResultsMean exogenous CHO oxidation rates were comparable with lactose (0.56 ± 0.19 g·min−1) and sucrose (0.61 ± 0.10 g·min−1; 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).ConclusionsLactose 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.

Exercise intensity regulates the effect of heat stress on substrate oxidation rates during exercise

Hyperthermia stimulates endogenous carbohydrate metabolism during exercise; however, it is not known if exercise intensity impacts the metabolic effect of heat stress. In the first study of this two-part investigation, endurance-trained male cyclists performed incremental exercise assessments in 18 and 35°C (60% rH). The stimulatory effect of heat stress on carbohydrate oxidation rates was greater at high vs. moderate vs. low relative intensity (P < 0.05). In agreement, no effects of heat stress on carbohydrate oxidation rates were observed during 60-min of subsequent low-intensity cycling. In study two, endurance-trained male cyclists performed 20-min of moderate-intensity (power at the first ventilatory threshold) and 5-min of high-intensity (power at the second ventilatory threshold) cycling in 18, 28, 34, and 40°C (60% rH). At moderate-intensity, carbohydrate oxidation rates were significantly elevated by heat stress in 40°C (P < 0.05), whereas at high-intensity carbohydrate oxidation rates were significantly elevated by heat stress in 34 and 40°C (P < 0.05). This exercise intensity-mediated regulation of the effect of heat stress on carbohydrate oxidation may be partially attributable to observed plasma adrenaline responses. Our data suggest that under moderate environmental heat stress (34–35°C, 60% rH), heat stress-induced changes in CHO oxidation rates are unlikely to occur unless the relative exercise intensity is high (81 ± 8%⩒O2max), whereas under more extreme environmental heat stress (40°C, 60% rH), these changes occur at lower relative intensities (69 ± 8%⩒O2max). This provides indication of when heat stress-induced metabolic changes during exercise are likely to occur.

Influences of a Cold and Warm Environment on Substrate Metabolism in Women during Running and Cycling

BackgroundWomen oxidize more fat than men at rest and during exercise due to differences in hormonal and blood flow regulatory mechanisms, as well as substrate storage and mobilization. Exercise studies examining the effects of varying environments on energy metabolism have consistently demonstrated a greater shift towards lipid utilization in cold compared to warm environments in men. In addition, these studies have been conducted at fixed exercise intensities and workloads only, and have not been validated with different exercise modalities. Thereby, this study aimed to determine whether cold and warm ambient temperatures influence fat and CHO oxidation across a range of exercise intensities during treadmill and cycle ergometer exercise in women.MethodsTwelve women (age 22 ± 1.8 yrs, weight 61 ± 6.6 kg, height 1.6 ± 0.09 m, body fat 26 ± 4.7 %, FFM 45 ± 5.8 kg, body surface area 1.6 ± 0.12 m2, and V̇O2 48 ± 5.1 mlO2·kg−1·min−1) completed four trials, one week apart, during which they performed an incremental peak oxygen consumption (V̇O2peak) test on a cycle ergometer or treadmill in a cold (5°C) or warm (35°C) environment. Cardiorespiratory and oxidation variables, including V̇O2, maximal fat oxidation rate (MFO), exercise intensity where MFO occurs (Fatmax), and relative contribution of lipids and carbohydrates (CHO) to total energy expenditure crossover point (CC) were assessed via indirect calorimetry. Lactate pre and post tests was also assessed. Analyses of variances and multiple linear regressions were performed.ResultsMFO was greater in the cold vs. warm for treadmill (0.51 ± 0.19 vs. 0.41 ± 0.14 g•min−1; p=0.04) but not during cycling (0.32 ± 0.14 vs. 0.23 ± 0.07 g•min−1; p=0.08). MFO was also greater during treadmill vs. cycling exercise, in both temperatures (0.46 ± 0.16 g•min−1 vs. 0.28 ± 0.11 g•min−1; p&lt;0.001). Fatmax was greater in the cold vs. warm within treadmill (63 ± 27 vs. 49 ± 22 % V̇O2max; p=0.02) but not cycling (41 ± 20 vs. 31 ± 12 % V̇O2max; p=0.16). CC was greater in the cold vs. warm within treadmill exercise (53 ± 20 vs. 39 ± 17% V̇O2max; p=0.04) but not during cycling (36 ± 12 vs. 28 ± 10% V̇O2max; p=0.19). Multiple linear regressions further revealed a strong influence of ambient temperature on lipids (p&lt;0.001) and CHO (p&lt;0.001) oxidation rates across exercise intensities.ConclusionsExercising in a cold environment increased MFO, Fatmax, and CC during treadmill exercise in women but not during cycling. These results imply that ambient temperature influences energy metabolism over a wide range of exercise intensities during treadmill exercise in women, similarly to what is seen in men. The large variability in fat oxidation in the present results, similar to other studies, will need to be investigated further in both women and men.Support or Funding InformationThis work was supported by a Laurentian University Research Fund grant.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Influence of low versus moderate glycemic index of diet on substrate oxidation and energy expenditure during incremental exercise in endurance athletes: a randomized counterbalanced cross-over trial

The study was aimed at assessing the influence of 3-week low glycemic index (LGI) versus moderate glycemic index (MGI) diet on substrate oxidation during incremental exercise. 17 runners completed two 3-week trials of either LGI or MGI diet in a randomised counterbalanced manner. Before and after each trial the incremental cycling test was performed. Metabolic alternations were observed only within tested diets and no significant differences in fat and carbohydrate (CHO) oxidation were found between MGI and LGI diets. Following MGI diet CHO oxidation rate increased. The AUC of fat oxidation decreased after both diets. Percent contribution of fat to energy yield declined, whereas contribution of CHO was augmented following MGI diet. This study indicates that the 3-week MGI diet increased the rate of carbohydrate oxidation during incremental cycling test and improved performance in acute intense exercise test, while both high-carbohydrate diets downregulated fat oxidation rate.

Re-examination of the contribution of substrates to energy expenditure during high-intensity intermittent exercise in endurance athletes.

BackgroundIt has been believed that the contribution of fat oxidation to total energy expenditure is becoming negligible at higher exercise intensities (about 85% VO2max). The aim of the present study was to examine the changes in substrate oxidation during high-intensity interval exercise in young adult men.MethodsA total of 18 healthy well-trained (aged 19.60 ± 0.54 years, BMI = 22.19 ± 0.64 kg/m2, n = 10) and untrained (aged 20.25 ± 0.41 years, BMI = 22.78 ± 0.38 kg/m2, n = 8) young men volunteered to participate in this study. After an overnight fast, subjects were tested on a cycle ergometer and completed six 4-min bouts of cycling (at ∼80% VO2max) with 2 min of rests between intervals. Energy expenditure and the substrate oxidation rate were measured during the experiment by using indirect calorimetry. The blood lactate concentration was collected immediately after each interval workout.ResultsThe fat oxidation rate during each workout was significantly different between the untrained and the athlete groups (p < 0.05), and the carbohydrate (CHO) oxidation rate during the experiment was similar between groups (p > 0.05). Moreover, lactate concentration significantly increased in the untrained group (p < 0.05), whereas it did not significantly change in the athlete group during the workouts (p > 0.05). Fat contribution to energy expenditure was significantly higher in the athlete group (∼25%) than in the untrained group (∼2%).ConclusionsThe present study indicates that 17 times more fat oxidation was measured in the athlete group compared to the untrained group. However, the athletes had the same CHO oxidation rate as the recreationally active subjects during high-intensity intermittent exercise. Higher fat oxidation rate despite the same CHO oxidation rate may be related to higher performance in the trained group.

Co-ingestion Of Glucose And Fructose During Exercise On Acute Exposure To Altitude

The reduction in partial pressure of oxygen (O2) leading to reduced O2 delivery to tissues at altitude has the potential to alter substrate utilization during exercise. Experiments at sea level suggest performance benefits from consuming multiple transportable carbohydrates, the impact of this at altitude is not known. PURPOSE: To investigate how carbohydrate (CHO) (glucose and fructose) ingestion effects fuel utilization during exercise at 2500m and the impact of this on performance. METHODS: Ingestion of 1.2 g.min-1 glucose plus 0.8 g.min-1 fructose was compared to 1.2 g.min-1 glucose and a placebo during 120 minutes running at 70% V[Combining Dot Above]O2max performed by eight males in a normobaric hypoxic chamber set at 2500m altitude. Exogenous and endogenous oxidation was quantified using 13C stable mass isotope tracing techniques. Performance was measured in a 5 km TT. RESULTS: CHO ingestion shifted fuel use to predominantly CHO (79.51 ± 7.11, 79.45 ± 1.88 and 56.66 ± 20.18% in glucose plus fructose, glucose alone and placebo, respectively) compared with placebo where fat (20.49 ± 7.11, 20.55 ± 11.88 and 43.34 ± 20.18% in glucose plus fructose, glucose alone and placebo, respectively) was the dominant fuel. Co-ingestion of glucose and fructose led to significantly (p< 0.001; ES= 3.82) greater peak exogenous CHO oxidation rates compared to glucose alone (1.51 ± 0.14 g.min-1 and 0.96 ± 0.07 g.min-1, respectively) and this resulted in a significantly (p= 0.007; ES= 1.01) lower contribution from endogenous CHO oxidation (49.15 ± 8.85% and 59.65 ± 1.80%, respectively). Co-ingestion of glucose and fructose did not improve performance in the 5 km TT (25:37 ± 03:01 minutes) compared to glucose alone (25:13 ± 02:53 minutes). However, time to complete the 5 km TT was significantly (p= 0.002; ES= 0.47) faster in the glucose only trial compared to placebo (26:33 ± 2:59 minutes). CONCLUSION: CHO ingestion reduced the reliance on fat oxidation compared to placebo and the co-ingestion of glucose and fructose increased exogenous and spared endogenous CHO oxidation over glucose alone. However, the co-ingestion of glucose and fructose did not provide an ergogenic benefit at 2500m.

Effect of a Carbohydrate Mouth Rinse on Plasma Glucose and Plasma Insulin during a 40‐km Cycling Time Trial

Rinsing the mouth with a carbohydrate solution, without ingesting, improves exercise performance of up to an hour in duration. Performance gains are attributed to the activation of brain regions associated with motivation and motor control. In addition to this neural response, a hormonal cascade may also be present, and include a cephalic‐phase insulin response from oral carbohydrate recognition.PURPOSEThe aim of this study was to examine whether exercise performance gains achieved through a carbohydrate mouth rinse are the partial result of a cephalic‐phase insulin response from oral carbohydrate recognition.METHODSEight trained, competitive cyclists [age (mean ± SEM) = 24 ± 2 y; VO2max = 64.5 ± 2.8 ml/kg/min] completed three simulated, 40‐km time trials comprised of a familiarization trial, carbohydrate mouth rinse trial (CHO) and placebo trial (PLA). Mouth rinse was administered prior to onset of exercise, and every 5‐km throughout exercise. During CHO and PLA trials, plasma glucose and plasma insulin samples were obtained immediately prior to mouth rinsing procedures. Metabolic data and cycling time were collected throughout the exercise session. CHO oxidation rates were calculated based on the equation: g/min = 4.210 VCO2 – 2.962 VO2, while fat oxidation rates were calculated based on: (g/min) = 1.695 VO2 – 1.701 VCO2 (Jeukendrup 2005).RESULTSTime to completion was faster for CHO (67.1 ± 1.1 sec) compared to PLA (67.9 ± 1.0 sec). Plasma glucose did not differ between conditions (p = 0.801) and held steady throughout exercise; additionally, respiratory exchange ratio was not statistically different between conditions (p = 0.081). There was no change in plasma insulin either within trials or between trials (p = 0.638). CHO oxidation rates were not statistically different (p = 0.06) between the CHO (3.43 ± 0.80 g/min) and PLA (2.98 ± 0.18 g/min) groups; fat oxidation rates were not statistically different (p = 0.10) between the CHO (0.59 ± 0.09) and PLA (0.76 ± 0.06) groups.CONCLUSIONSRinsing the mouth with a carbohydrate solution prior to exercise and after each 5‐km interval improved 40‐km time trial performance. This finding shows that improved exercise performance occurs independent of changes in plasma glucose, plasma insulin, RER, or substrate oxidation rates. These findings build on previous research to support the notion of a CHO mouth rinse having primarily a neurological response (Chambers 2009), and not acting via a cephalic‐phase insulin response, in order to improve exercise performance.Support or Funding InformationIndiana University – School of Public Health Student Research Grant Award ‐ March 2016 ($1000)BK Betty Stevens Award (UF funding for trip to Experimental Biology 2017)

CHO Mouth Rinse Ameliorates Neuromuscular Response with Lower Endogenous CHO Stores.

This study aimed to investigate carbohydrate (CHO) mouth rinse response on neuromuscular activity, fuel oxidation rates, and cycling performance with different initial levels of endogenous CHO availability. In a double-blind, randomized placebo-controlled design, eight males completed six experimental mouth rinse trials: CHO (6.4% maltodextrin) or placebo solution in a fed state (FED), 12-h fasted state (FAST), or a combined exercise-depleted muscle glycogen and 12-h fasted state (DEP). Trials consisted of 30-min cycling at 90% of gas exchange threshold, followed by a 20-km cycling time trial. Plasma lactate, plasma glucose, oxygen uptake, and EMG activity were measured, and CHO and fat oxidation rates were calculated. CHO mouth rinse maintained higher plasma glucose levels as the constant load exercise progressed (P = 0.023). The reduced EMG activity in the DEP condition with the placebo during constant load exercise was ameliorated with CHO mouth rinse (P < 0.01). Furthermore, the power output and the EMG activity throughout the 20-km time trial were reduced in the DEP condition with placebo but were both restored with CHO mouth rinse (P < 0.05). Time trial performance was only improved with CHO in the DEP compared with the corresponding placebo (P < 0.05), and no differences between supplements were observed in the FED or FAST states. Analyses of the qualitative inference showed "benefit very likely" of CHO mouth rinse on exercise performance in DEP, "possibly benefit" in FAST, and "negligible or trivial" in FED. CHO mouth rinse had no effect on CHO and fat oxidation rates in either exercise mode. The CHO mouth rinse influences exercise performance when endogenous CHO availability is low, and an enhanced central motor drive is potentially the main influencing mechanism.