Carbohydrate, protein and fat metabolism during exercise after oral carnitine supplementation in humans

Twenty non-vegetarian active males were pair-matched and randomly assigned to receive 2 g L-Carnitine L-tartrate (LC).d-1 or placebo for 2 weeks. Subjects exercised for 90 min at 70% O2max following 2 days of a prescribed diet (mean ± SD: 13.6 ± 1.6 MJ, 57% carbohydrate, 15% protein, 26% fat, 2% alcohol) before and after supplementation. Results indicated no change in carbohydrate oxidation, nitrogen excretion, branched-chain amino acid oxidation, or plasma urea during exercise between the beginning and end of supplementation in either group. Following 2 weeks LC supplementation the plasma ammonia response to exercise tended to be suppressed (0 vs. 2wk at 60 min exercise: 97 ± 26 vs. 80 ± 9; and 90 min exercise: 116 ± 47 vs. 87 ± 25 µmol.L-1), with no change in the placebo group. The data indicate that 2 weeks of LC supplementation does not affect fat, carbohydrate and protein contribution to metabolism during prolonged moderate intensity cycling exercise. However, the tendency towards suppressed ammonia accumulation indicates that oral LC supplementation may have the potential to reduce the metabolic stress of exercise or alter ammonia production/removal which warrants further investigation

Effects of exercise intensity and altered substrate availability on cardiovascular and metabolic responses to exercise after oral carnitine supplementation in athletes

The effects of 15 d of supplementation with L-carnitine L-tartrate (LC) on metabolic responses to graded-intensity exercise under conditions of altered substrate availability were examined. Fifteen endurance-trained male athletes undertook exercise trials after a 2-d high-carbohydrate diet (60% CHO, 25% fat) at baseline (D0), on Day 14 (D14), and after a single day of high fat intake (15% CHO, 70% fat) on Day 15 (D15) in a double-blind, placebo-controlled, pair-matched design. Treatment consisted of 3 g LC (2 g L-carnitine/d; n = 8) or placebo (P, n = 7) for 15 d. Exercise trials consisted of 80 min of continuous cycling comprising 20-min periods at each of 20%, 40%, 60%, and 80% VO2peak. There was no significant difference between whole-body rates of CHO and fat oxidation at any workload between D0 and D14 trials for either the P or LC group. Both groups displayed increased fat and reduced carbohydrate oxidation between the D14 and D15 trials (p less than .05). During the D15 trial, heart rate (p less than .05 for 20%, 40%, and 60% workloads) and blood glucose concentration (p less than .05 for 40% and 60% workloads) were lower during exercise in the LC group than in P. These responses suggest that LC may induce subtle changes in substrate handling in metabolically active tissues when fatty-acid availability is increased, but it does not affect whole-body substrate utilization during short-duration exercise at the intensities studied

Optimizing the restoration and maintenance of fluid balance after exercise-induced dehydration

Hypohydration, or a body water deficit, is a common occurrence in athletes and recreational exercisers following the completion of an exercise session. For those who will undertake a further exercise session that day, it is important to replace water losses to avoid beginning the next exercise session hypohydrated and the potential detrimental effects on performance that this may lead to. The aim of this review is to provide an overview of the research related to factors that may affect post-exercise rehydration. Research in this area has focused on the volume of fluid to be ingested, the rate of fluid ingestion and on fluid composition. Volume replacement during recovery should exceed that lost during exercise to allow for ongoing water loss however ingestion of large volumes of plain water results in a prompt diuresis, effectively preventing longer term maintenance of water balance. Addition of sodium to a rehydration solution is beneficial for maintenance of fluid balance due to its effect on extracellular fluid osmolality and volume. The addition of macronutrients, such as carbohydrate and protein, can promote maintenance of hydration by influencing absorption and distribution of ingested water which, in turn, effects extracellular fluid osmolality and volume. Alcohol is commonly consumed in the post-exercise period and may influence post-exercise rehydration as will the co-ingestion of food. Future research in this area should focus on providing information related to optimal rates of fluid ingestion, advisable solutions to ingest during different duration recovery periods and confirmation of mechanistic explanations for the observations outlined

Effect of exercise and heat-induced hypohydration on brain volume

Purpose: The aim of the present study was to quantify changes in brain volume following exercise/heat-induced hypohydration in man. Methods: Eight active men completed intermittent exercise in a warm environment, until 2.9 ± 0.1 % of body mass was lost. Subjects remained hypohydrated for two hours following the end of exercise. Brain volume was measured before, immediately following, and 1h and 2h after exercise using MRI (Philips 3T Achieva). Measures of subjective feelings and core body temperature were also monitored. Blood samples were drawn to determine serum electrolyte concentrations and osmolality and to allow calculation of changes in blood and plasma volumes. Results: Brain volume was not influenced by hypohydration (0.2 ± 0.4 %; ES 0.2; P = 0.310). Reductions in ventricular (4.0 ± 1.8 %; ES 4.6; P < 0.001) and CSF (3.1 ± 1.9%; ES 3.3; P = 0.003) volumes were observed following exercise. Compared with pre-exercise levels, serum osmolality was elevated throughout the 2h post-exercise period (+10 ± 2 mosmol/kg; P < 0.001). Core temperature increased from 37.1 ± 0.3oC at rest to 39.3 ± 0.5oC at the end of exercise (P = 0.001). Conclusions: These data demonstrate that brain volume remains unchanged in response to moderate hypohydration and the presence of serum hyperosmolality, suggesting that mechanisms are in place to defend brain volume

Mild hypohydration increases the frequency of driver errors during a prolonged, monotonous driving task

The aim of the present study was to examine the effect of mild hypohydration on performance during a prolonged, monotonous driving task. Methods: Eleven healthy males (age 22 ± 4 y) were instructed to consume a volume of fluid in line with published guidelines (HYD trial) or 25% of this intake (FR trial) in a crossover manner. Participants came to the laboratory the following morning after an overnight fast. One hour following a standard breakfast, a 120 min driving simulation task began. Driver errors, including instances of lane drifting or late breaking, EEG and heart rate were recorded throughout the driving task. Results: Pre-trial bodymass (P=0.692), urine osmolality (P=0.838) and serumosmolality (P=0.574)were the same on both trials. FR resulted in a 1.1±0.7% reduction in bodymass, compared to−0.1±0.6% in the HYD trial (P = 0.002). Urine and serum osmolality were both increased following FR (P b 0.05). There was a progressive increase in the total number of driver errors observed during both the HYD and FR trials, but significantly more incidents were recorded throughout the FR trial (HYD 47 ± 44, FR 101 ± 84; ES = 0.81; P = 0.006). Conclusions: The results of the present study suggest that mild hypohydration, produced a significant increase in minor driving errors during a prolonged, monotonous drive, compared to that observed while performing the same task in a hydrated condition. The magnitude of decrement reported,was similar to that observed following the ingestion of an alcoholic beverage resulting in a blood alcohol content of approximately 0.08% (the current UK legal driving limit), or while sleep deprived

A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index

BACKGROUND: The identification of beverages that promote longer-term fluid retention and maintenance of fluid balance is of real clinical and practical benefit in situations in which free access to fluids is limited or when frequent breaks for urination are not desirable. The postingestion diuretic response is likely to be influenced by several beverage characteristics, including the volume ingested, energy density, electrolyte content, and the presence of diuretic agents. OBJECTIVE: This study investigated the effects of 13 different commonly consumed drinks on urine output and fluid balance when ingested in a euhydrated state, with a view to establishing a beverage hydration index (BHI), i.e., the volume of urine produced after drinking expressed relative to a standard treatment (still water) for each beverage. DESIGN: Each subject (n = 72, euhydrated and fasted male subjects) ingested 1 L still water or 1 of 3 other commercially available beverages over a period of 30 min. Urine output was then collected for the subsequent 4 h. The BHI was corrected for the water content of drinks and was calculated as the amount of water retained at 2 h after ingestion relative to that observed after the ingestion of still water. RESULTS: Total urine masses (mean +/- SD) over 4 h were smaller than the still-water control (1337 +/- 330 g) after an oral rehydration solution (ORS) (1038 +/- 333 g, P < 0.001), full-fat milk (1052 +/- 267 g, P < 0.001), and skimmed milk (1049 +/- 334 g, P < 0.001). Cumulative urine output at 4 h after ingestion of cola, diet cola, hot tea, iced tea, coffee, lager, orange juice, sparkling water, and a sports drink were not different from the response to water ingestion. The mean BHI at 2 h was 1.54 +/- 0.74 for the ORS, 1.50 +/- 0.58 for full-fat milk, and 1.58 +/- 0.60 for skimmed milk. CONCLUSIONS: BHI may be a useful measure to identify the short-term hydration potential of different beverages when ingested in a euhydrated state. This trial was registered at www.isrctn.com as ISRCTN13014105

Exposure to high solar radiation reduces self-regulated exercise intensity in the heat outdoors

High radiant heat load reduces endurance exercise performance in the heat indoors, but this remains unconfirmed in outdoor exercise. The current study investigated the effects of variations in solar radiation on self-regulated exercise intensity and thermoregulatory responses in the heat outdoors at a fixed rating of perceived exertion (RPE). Ten male participants completed 45-min cycling exercise in hot outdoor environments (about 31 °C) at a freely chosen resistance and cadence at an RPE of 13 (somewhat hard). Participants were blinded to resistance, pedal cadence, distance and elapsed time and exercised at three sunlight exposure conditions: clear sky (mean ± SD: 1072 ± 91 W·m−2; HIGH); thin cloud (592 ± 32 W·m−2; MID); and thick cloud (306 ± 52 W·m−2; LOW). Power output (HIGH 96 ± 22 W; MID 103 ± 20 W; LOW 108 ± 20 W) and resistance were lower in HIGH than MID and LOW (P < .001). Pedal cadence was lower, the core-to-skin temperature gradient was narrower, body heat gain from the sun (SHG) was greater and thermal sensation was higher with increasing solar radiation and all variables were different between trials (P < .01). Mean skin temperature was higher in HIGH than MID and LOW (P < .01), but core temperature was similar between trials (P = .485). We conclude that self-regulated exercise intensity in the heat outdoors at a fixed RPE of somewhat hard is reduced with increasing solar radiation because of greater thermoregulatory strain, perceived thermal stress and SHG. This suggests that reduced self-selected exercise intensity during high solar radiation exposure in the heat may prevent excessive core temperature rise.PostprintPeer reviewe

Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015

The third International Exercise-Associated Hyponatremia (EAH) Consensus Development Conference convened in Carlsbad, California in February 2015 with a panel of 17 international experts. The delegates represented 4 countries and 9 medical and scientific sub-specialties pertaining to athletic training, exercise physiology, sports medicine, water/sodium metabolism, and body fluid homeostasis. The primary goal of the panel was to review the existing data on EAH and update the 2008 Consensus Statement.1 This document serves to replace the second International EAH Consensus Development Conference Statement and launch an educational campaign designed to address the morbidity and mortality associated with a preventable and treatable fluid imbalance. The following statement is a summary of the data synthesized by the 2015 EAH Consensus Panel and represents an evolution of the most current knowledge on EAH. This document will summarize the most current information on the prevalence, etiology, diagnosis, treatment and prevention of EAH for medical personnel, athletes, athletic trainers, and the greater public. The EAH Consensus Panel strove to clearly articulate what we agreed upon, did not agree upon, and did not know, including minority viewpoints that were supported by clinical experience and experimental data. Further updates will be necessary to both: (1) remain current with our understanding and (2) critically assess the effectiveness of our present recommendations. Suggestions for future research and educational strategies to reduce the incidence and prevalence of EAH are provided at the end of the document as well as areas of controversy that remain in this topic. [excerpt

A Pilot Study Investigating the Influence of Glucagon-Like Peptide-1 Receptor Single Nucleotide Polymorphisms on Gastric Emptying Rate in Caucasian Men

Gastric emptying rate in humans is subject to large individual variability, but previous research on the influence of genetics is scarce. Variation in the glucagon-like peptide-1 receptor (GLP1R) gene is a plausible candidate gene to partially explain the high variance. This study aimed to investigate the influence of genetic variation in the GLP1R gene on gastric emptying rate of a glucose solution in humans. Forty eight healthy Caucasian males took part in this investigation. Gastric emptying rate of a 6% glucose solution was assessed using the 13C breath test method and a venous blood sample was obtained from each participant. Participants were genotyped for 27 Tag single nucleotide polymorphisms (SNPs) in the GLP1R locus using Sequenom MassARRAY iPLEX GOLD analysis and MALDI-TOF mass spectrometry. The time at which maximal emptying rate occurred (Tlag) was faster in participants with the CC genotype than in TT and TC genotypes for SNP rs742764: [median (quartiles) CC, 35 (30–36) min vs. TT, 43 (39–46) min, and TC, 41 (39–45) min; P &lt; 0.01]. Tlag was also slower in participants with the AA genotype compared to the TT and TA genotypes for SNP rs2254336: [AA, 43 (39–49) min vs. TT, 36 (34–41) min, and TA, 39 (35–42) min; P &lt; 0.05]. Analysis by phenotype also showed differences in half-emptying time (T12) and Tlag for SNPs rs9283907, rs2268657, and rs2254336. Several neighboring Tag SNPs within the GLP1R gene were found to be associated with gastric emptying rate, and should be further investigated

Metabolic profiling of human saliva before and after induced physiological stress by ultra-high performance liquid chromatography-ion mobility-mass spectrometry

A method has been developed for metabolite profiling of the salivary metabolome based on protein precipitation and ultra-high performance liquid chromatography coupled with ion mobility-mass spectrometry (UHPLC–IM–MS). The developed method requires 0.5 mL of human saliva, which is easily obtainable by passive drool. Standard protocols have been established for the collection, storage and pre-treatment of saliva. The use of UHPLC allows rapid global metabolic profiling for biomarker discovery with a cycle time of 15 min. Mass spectrometry imparts the ability to analyse a diverse number of species reproducibly over a wide dynamic range, which is essential for profiling of biofluids. The combination of UHPLC with IM–MS provides an added dimension enabling complex metabolic samples to be separated on the basis of retention time, ion mobility and mass-to-charge ratio in a single chromatographic run. The developed method has been applied to targeted metabolite identification and untargeted metabolite profiling of saliva samples collected before and after exercise-induced physiological stress. δ-Valerolactam has been identified as a potential biomarker on the basis of retention time, MS/MS spectrum and ion mobility drift time