Comparison of caffeine and theophylline ingestion: exercise metabolism and endurance

The Relationship between Changes in MYBPC3 Single-Nucleotide Polymorphism-Associated Metabolites and Elite Athletes' Adaptive Cardiac Function

Athletic performance is a multifactorial trait influenced by a complex interaction of environmental and genetic factors. Over the last decades, understanding and improving elite athletes' endurance and performance has become a real challenge for scientists. Significant tools include but are not limited to the development of molecular methods for talent identification, personalized exercise training, dietary requirements, prevention of exercise-related diseases, as well as the recognition of the structure and function of the genome in elite athletes. Investigating the genetic markers and phenotypes has become critical for elite endurance surveillance. The identification of genetic variants contributing to a predisposition for excellence in certain types of athletic activities has been difficult despite the relatively high genetic inheritance of athlete status. Metabolomics can potentially represent a useful approach for gaining a thorough understanding of various physiological states and for clarifying disorders caused by strength-endurance physical exercise. Based on a previous GWAS study, this manuscript aims to discuss the association of specific single-nucleotide polymorphisms (SNPs) located in the MYBPC3 gene encoding for cardiac MyBP-C protein with endurance athlete status. MYBPC3 is linked to elite athlete heart remodeling during or after exercise, but it could also be linked to the phenotype of cardiac hypertrophy (HCM). To make the distinction between both phenotypes, specific metabolites that are influenced by variants in the MYBPC3 gene are analyzed in relation to elite athletic performance and HCM. These include theophylline, ursodeoxycholate, quinate, and decanoyl-carnitine. According to the analysis of effect size, theophylline, quinate, and decanoyl carnitine increase with endurance while decreasing with cardiovascular disease, whereas ursodeoxycholate increases with cardiovascular disease. In conclusion, and based on our metabolomics data, the specific effects on athletic performance for each MYBPC3 SNP-associated metabolite are discussed.

Effects of theophylline on ADCY5 activation-From cellular studies to improved therapeutic options for ADCY5-related dyskinesia patients

We show the effects of the three purine derivatives, caffeine, theophylline, and istradefylline, on cAMP production by adenylyl cyclase 5 (ADCY5)-overexpressing cell lines. A comparison of cAMP levels was performed for ADCY5 wild-type and R418W mutant cells. ADCY5-catalyzed cAMP production was reduced with all three purine derivatives, while the most pronounced effects on cAMP reduction were observed for ADCY5 R418W mutant cells. The gain-of-function ADCY5 R418W mutant is characterized by an increased catalytic activity resulting in elevated cAMP levels that cause kinetic disorders or dyskinesia in patients. Based on our findings in ADCY5 cells, a slow-release formulation of theophylline was administered to a preschool-aged patient with ADCY5-related dyskinesia. A striking improvement of symptoms was observed, outperforming the effects of caffeine that had previously been administered to the same patient. We suggest considering theophylline as an alternative therapeutic option to treat ADCY5-related dyskinesia in patients.

Effects of caffeinated beverage ingestion on salivary antimicrobial proteins responses to acute exercise in the heat

Caffeine is commonly used by athletes as an energy supplement, but studies on its effects on salivary antimicrobial proteins (sAMPs) in humans during exercise are rare with ambiguous findings. It is also still controversial whether hot environments affect sAMPs. Using a double-blind, randomized crossover design, we examined 12 endurance-trained male collegiate athletes who completed the following two experiments: a caffeine experiment (CAF) and a placebo experiment (PLA). The participants acutely consumed caffeine-containing (6 mg/kg body weight) sports drink (3 ml/kg body weight) or an equivalent amount of placebo sports drink and subsequently performed cycling exercise for 40 min in the heat (33 ± 0.24°C, 64 ± 2.50% relative humidity) at 50% of maximum output power, maintaining a pedal frequency of 60 rpm. Saliva was collected at 60 min pre-exercise (T–60), the start of exercise (T0), 20 min of exercise (T20), and the end of the exercise (T40), and salivary α-amylase (sAA) and lactoferrin (sLac) were tested. The rating of perceived exertion (RPE) was measured at T0–T40, while core body temperature (Tre) and heart rate (HR) were monitored continuously. Tre, HR, and RPE increased with time during the exercise (p < 0.01), with no difference in Tre and HR between the CAF and PLA (p > 0.05), but RPE was higher in the PLA than in the CAF (p < 0.05). sLac concentrations were significantly higher at T20 and T40 than at T–60 (p < 0.01) and higher at T40 than at T0 and T20 (p < 0.01), with no difference between the CAF and PLA (p > 0.05). Compared with T–60, sAA activity was significantly increased at T0, T20, and T40 (p < 0.01). sAA activity was significantly higher at T40 than at T0 and T20 (p < 0.01), at T20 than at T0 (p < 0.05), and in the CAF than in the PLA (p < 0.01). Heat stress caused by acute exercise in hot environments did not impair the sAMPs parameters of the participants. Instead, the participants showed transient increase in sAA activity and unchanged sLac concentrations. Caffeine may increase salivary markers related to immune response during exercise.

Investigation of potential behavioral and physiological effects of caffeine on D. magna

With the ever-increasing consumption of pharmaceutical compounds, their presence in the environment is now an undisputable reality. The majority of these compounds are released into the wild after their therapeutic use, as biotransformation products or in their original form. The presence of this class of compounds in the environment, due to their biological properties, can exert effects on non-target organisms, with adverse consequences. In addition, some bioactive substances, such as stimulants of the central nervous system, are also used by humans as part of their diet. The adverse consequences posed by such chemicals may be permanent or transient, if the exposure to xenobiotics is halted; it is thus of the paramount importance to study effects that result from long-term exposure to toxicants, but also the recovery of organisms previously exposed to such substances, especially if such chemicals may cause some type of addiction. Caffeine (1,3,7-trimethylxanthine) is a naturally occurring alkaloid found in many plants, being one of the most common stimulant/pharmaceutical compounds found in the environment. In addition, it is addictive, and strongly consumed by humans, a factor that contributes also for its continuous presence in the aquatic environment. The aim of this study was to evaluate the effects of environmentally relevant concentrations (0.08; 0.4; 2; 10; and 50 μg/L) of caffeine on behavior and physiological parameters (that are proxies of metabolic traits, such as oxygen uptake and glycogen content), in individuals of the freshwater crustacean species Daphnia magna, of distinct ages, and with or without a recovery period in the absence of caffeine. Regarding behavior, the results indicated that caffeine exposure altered the moved distance of the test organisms, but not according to a coherent pattern; low concentrations of caffeine reduced the movement of exposed daphnids, while higher levels did not have any measurable effect on this parameter. In addition, it was possible to identify subtle withdrawal effects (animals exposed to caffeine during 21 days and kept in uncontaminated media for 2 days). Regarding the other two studied parameters, caffeine exposure did not result in any significant modification in oxygen uptake and glycogen stores/reserves of the test organisms, in animals continuously exposed, or in those subjected to a recovery period, suggesting that despite a behavioral stimulatory effect, this was not followed by any metabolic change, and no addictive effect was possible to infer. The results showed that the presence of caffeine in environmental concentrations can induce mild behavioral effects at low, albeit realistic levels, but not capable of establishing clear biochemical changes.

Effects of theophylline and theobromine on exercise performance and implications for competition sport: A systematic review

A systematic review was undertaken to evaluate studies on the effects of theophylline and theobromine on exercise performance in normal (healthy) subjects. Theophylline was found to have been studied on eight occasions and theobromine on one, the number of subjects per study ranging from seven to 15. In two exercise investigations, theophylline was superior to placebo at a p < 0.05 level and no different in four including one that was conducted in artificial hypoxia. In a treadmill time trial over 3 km, theobromine was superior to placebo and equal to caffeine, at the <0.05 level. In strength studies, theophylline increased wrist strength in one and showed a slight but not statistically significant increase in limb strength in four of the seven subjects in the other. Theophylline caused adverse effects in six participants. There were no adverse effects in the theobromine investigation. Although the studies showed contradicting results and/or insufficient data to draw solid conclusions, it appears both drugs have potential to enhance performance and could be considered for inclusion on the WADA banned list.

Effect of Acute Caffeine Intake on the Fat Oxidation Rate during Exercise: A Systematic Review and Meta-Analysis

A number of previous investigations have been designed to determine the effect of acute caffeine intake on the rate of fat oxidation during exercise. However, these investigations have shown contradictory results due to the differences in the exercise protocols used or the co-ingestion of caffeine with other substances. Hence, to date, there is no consensus about the effect of caffeine on fat oxidation during exercise. The purpose of this study was to conduct a systematic review followed by a meta-analysis to establish the effect of acute intake of caffeine (ranging from 2 to 7 mg/kg of body mass) on the rate of fat oxidation during exercise. A total of 19 studies published between 1978 and 2020 were included, all of which employed crossover experimental designs in which the ingestion of caffeine was compared to a placebo. Studies were selected if the exercise intensity was consistent in the caffeine and placebo trials and if these were preceded by a fasting protocol. A subsequent meta-analysis was performed using the random effects model to calculate the standardized mean difference (SMD). The meta-analysis revealed that caffeine significantly (p = 0.008) increased the fat oxidation rate (SMD = 0.73; 95% CI = 0.19 to 1.27). This increment was consistent with a significant (p = 0.04) reduction of the respiratory exchange ratio (SMD = -0.33; 95% CI = -0.65 to -0.01) and a significant (p = 0.049) increase in the oxygen uptake (SMD = 0.23; 95% CI = 0.01 to 0.44). The results also showed that there was a dose-response effect of caffeine on the fat oxidation rate, indicating that more than 3.0 mg/kg is necessary to obtain a statistically significant effect of this stimulant on fat oxidation during exercise. Additionally, the ability of caffeine to enhance fat oxidation during exercise was higher in sedentary or untrained individuals than in trained and recreational athletes. In conclusion, pre-exercise intake of a moderate dose of caffeine may effectively increase fat utilization during aerobic exercise of submaximal intensity performed after a fasting period. However, the fitness level of the participant may modulate the magnitude of the effect of caffeine on fat oxidation during exercise.

Non-carbohydrate Dietary Factors and Their Influence on Post-Exercise Glycogen Storage: a Review

The optimization of post-exercise glycogen synthesis can improve endurance performance, delay fatigue in subsequent bouts, and accelerate recovery from exercise. High carbohydrate intakes (1.2 g/kg of body weight/h) are recommended in the first 4 h after exercise. However, athletes may struggle to consume carbohydrates at those levels. PURPOSE OF REVIEW: Thus, we aimed to determine whether the consumption of non-carbohydrate dietary factors (creatine, glutamine, caffeine, flavonoids, and alcohol) enhances post-exercise glycogen synthesis. RECENT FINDINGS: Trained athletes may not realize the benefits of creatine loading on glycogen synthesis. The impacts of caffeine, glutamine, flavonoids, and alcohol on post-exercise glycogen synthesis are poorly understood. Other ergogenic benefits to exercise performance, however, have been reported for creatine, glutamine, caffeine, and flavonoids, which were beyond the scope of this review. Evidence in trained athletes is limited and inconclusive on the impact of these non-carbohydrate dietary factors on post-exercise glycogen synthesis.

Low caffeine dose improves intermittent sprint performance in hot and humid environments

While the effects of caffeine have been evaluated in relation to endurance exercise, few studies have assessed the ergogenic effects of low caffeine doses on intermittent exercise performance in hot and humid environments. Thus, we aimed to determine the effects of low-dose caffeine supplementation on intermittent exercise performance under these conditions. Eight male soccer players (age, 19.9 ± 0.3 years; height, 173.7 ± 6.3 cm; body mass, 65.1 ± 5.5 kg; V˙O₂max, 50.0 ± 3.1 mL ⋅ kg^-1⋅ min^-1) participated in this double-blind, randomized, cross-over study. Caffeine was orally administered at 60 min before exercise (dosage, 3 mg ⋅ kg^-1). The participants completed a 90-min intermittent sprint cycling protocol under two conditions (after receiving caffeine and placebo) at 32 °C and at 70% relative humidity. A significant improvement in the total amount of work was observed in the caffeine condition compared to the placebo condition (155.0 ± 15.8 vs 150.8 ± 14.5 kJ, respectively; p < 0.05, d = 0.28). In contrast, the rectal temperature measured at the end of exercise showed no significant difference between the conditions (38.9 ± 0.4 °C and 38.7 ± 0.5 °C in the caffeine and placebo conditions, respectively; p > 0.05, d = 0.57). Other thermal responses, such as the mean skin temperature, heart rate, or sweat volume, were not significantly different between these conditions. These results suggested that a low caffeine dose improved the intermittent sprint performance and the reasons could be explained by the fact that a low caffeine dose ingestion did not affect the thermoregulatory responses compared to the placebo condition and, thus, did not attenuate its ergogenic effect on exercise in hot and humid environments.

No individual or combined effects of caffeine and beetroot-juice supplementation during submaximal or maximal running

Dietary supplements such as caffeine and beetroot juice are used by athletes in an attempt to optimize performance and therefore gain an advantage in competition. The aim of this study was to investigate the individual and combined effects of caffeine and beetroot-juice supplementation during submaximal and maximal treadmill running. Seven males (maximal oxygen uptake: 59.0 ± 2.9 mL·kg–1·min–1) and 2 females (maximal oxygen uptake: 53.1 ± 11.4 mL·kg–1·min–1) performed a preliminary trial followed by 4 experimental test sessions. Each test session consisted of two 5-min submaximal running bouts (at ∼70% and 80% of maximal oxygen uptake) and a maximal 1-km time trial (TT) in a laboratory. Participants ingested 70 mL of concentrated beetroot juice containing either 7.3 mmol of nitrate (BR) or no nitrate (PBR) 2.5 h prior to each test session, then either caffeine (C) at 4.8 ± 0.4 (4.3–5.6) mg/kg of body mass or a caffeine placebo (PC) 45 min before each test session. The 4 test sessions (BR-C, BR-PC, PBR-C, and PBR-PC) were presented in a counterbalanced and double-blind manner. No significant differences were identified between the 4 interventions regarding relative oxygen uptake, running economy, respiratory exchange ratio, heart rate (HR), or rating of perceived exertion (RPE) at the 2 submaximal intensities (P > 0.05). Moreover, there were no significant differences in performance, maximum HR, peak blood lactate concentration, or RPE during the maximal TT when comparing the interventions (P > 0.05). In conclusion, no beneficial effects of supplementing with typical doses of caffeine, beetroot juice, or a combination of the two were observed for physiological, perceptual, or performance responses during submaximal or maximal treadmill running exercise.

Caffeine and Physiological Responses to Submaximal Exercise: A Meta-Analysis

The aim of this study was to carry out a systematic review and meta-analysis of the effects of caffeine supplementation on physiological responses to submaximal exercise. A total of 26 studies met the inclusion criteria of adopting double-blind, randomized crossover designs that included a sustained (5-30 min) fixed-intensity bout of submaximal exercise (constrained to 60-85% maximal rate of oxygen consumption) using a standard caffeine dose of 3-6 mg·kg^-1 administered 30-90 min prior to exercise. Meta-analyses were completed using a random-effects model, and data are presented as raw mean difference (D) with associated 95% confidence limits (CLs). Relative to placebo, caffeine led to significant increases in submaximal measures of minute ventilation (D = 3.36 L·min^-1; 95% CL, 1.63-5.08; P = .0001; n = 73), blood lactate (D = 0.69 mmol·L^-1; 95% CL, 0.46-0.93; P < .00001; n = 208), and blood glucose (D = 0.42 mmol·L^-1; 95% CL, 0.29-0.55; P < .00001; n = 129). In contrast, caffeine had a suppressive effect on ratings of perceived exertion (D = -0.8; 95% CL, -1.1 to -0.6; P < .00001; n = 147). Caffeine had no effect on measures of heart rate (P = .99; n = 207), respiratory exchange ratio (P = .18; n = 181), or oxygen consumption (P = .92; n = 203). The positive effects of caffeine supplementation on sustained high-intensity exercise performance are widely accepted, although the mechanisms to explain that response are currently unresolved. This meta-analysis has revealed clear effects of caffeine on various physiological responses during submaximal exercise, which may help explain its ergogenic action.

Pharmacological potential of methylxanthines: Retrospective analysis and future expectations

Methylated xanthines (methylxanthines) are available from a significant number of different botanical species. They are ordinarily included in daily diet, in many extremely common beverages and foods. Caffeine, theophylline and theobromine are the main methylxanthines available from natural sources. The supposedly relatively low toxicity of methylxanthines, combined with the many beneficial effects that have been attributed to these compounds through time, generated a justified attention and a very prolific ground for dedicated scientific reports. Methylxanthines have been widely used as therapeutical tools, in an intriguing range of medicinal scopes. In fact, methylxanthines have been/were medically used as Central Nervous System stimulants, bronchodilators, coronary dilators, diuretics and anti-cancer adjuvant treatments. Other than these applications, methylxanthines have also been hinted to hold other beneficial health effects, namely regarding neurodegenerative diseases, cardioprotection, diabetes and fertility. However, it seems now consensual that toxicity concerns related to methylxanthine consumption and/or therapeutic use should not be dismissed. Taking all the knowledge and expectations on the potential of methylxanthines into account, we propose a systematic look at the past and future of methylxanthine pharmacologic applications, discussing all the promise and anticipating possible constraints. Anyways, methylxanthines will still substantiate considerable meaningful research and discussion for years to come.

Acute hematological and mood perception effects of bitter orange extract (p-synephrine) consumed alone and in combination with caffeine: A placebo-controlled, double-blind study

The purpose of this study was to examine acute hematological and mood perception responses to supplementation with p-synephrine alone and in combination with caffeine during quiet sitting. Sixteen subjects visited the laboratory on 6 occasions and were given (in randomized double-blind manner) 103-mg p-synephrine (S), 233-mg caffeine + 104-mg p-synephrine, 240-mg caffeine, 337-mg caffeine + 46-mg p-synephrine, 325-mg caffeine, or a placebo (PL). The subjects sat quietly for 3 hr while completing mood state questionnaires every 30 min. Venous blood samples were collected at baseline (pre) and 3 hr (post) to determine immune, lipid, and chemistry panels. Compared with PL, no significant supplement differences were observed during the S trial with the exception of differential time effects seen in hematocrit (decrease in PL, no change in S), triglycerides and very low-density lipoproteins (no changes in PL, significant decreases in S), and iron (no change in PL, significant elevation in S). Supplements containing caffeine showed increased feelings of attention, excitement, energy, and vigor. These data indicate that consumption of 103-mg p-synephrine does not negatively impact acute blood parameters, does not augment the effects of caffeine, or produce stimulant-like perceptual mood effects.

Spinal Cord Injury Level Influences Acute Plasma Caffeine Responses

PURPOSE

This study aimed to investigate the absorption curve and acute effects of caffeine at rest in individuals with no spinal cord injury (SCI), paraplegia (PARA), and tetraplegia (TETRA).

METHODS

Twenty-four healthy males (eight able-bodied [AB], eight PARA, and eight TETRA) consumed 3 mg·kg caffeine anhydrous (CAF) in a fasted state. Plasma caffeine [CAF], glucose, lactate, free fatty acid, and catecholamine concentrations were measured during a 150-min rest period.

RESULTS

Peak [CAF] was greater in TETRA (21.5 μM) compared with AB (12.2 μM) and PARA (15.1 μM), and mean peak [CAF] occurred at 70, 80, and 80 min, respectively. Moderate and large effect sizes were revealed for TETRA compared with PARA and AB (-0.55 and -1.14, respectively) for the total area under the [CAF] versus time curve. Large interindividual responses were apparent in SCI groups. The change in plasma catecholamine concentrations after CAF did not reach significance (P > 0.05); however, both adrenaline and noradrenaline concentrations were lowest in TETRA. Significant increases in free fatty acid were seen over time (P < 0.0005), but there was no significant influence of SCI level. Blood lactate concentration reduced over time (P = 0.022), whereas blood glucose concentration decreased modestly (P = 0.695), and no difference between groups was seen (P > 0.05).

CONCLUSION

The level of SCI influenced the caffeine absorption curve, and there was large interindividual variation within and between groups. Individual curves should be considered when using caffeine as an ergogenic aid in athletes with an SCI. The results indicate TETRA should trial low doses in training and PARA may consider consuming caffeine greater than 60 min before exercise performance. The study also supports caffeine's direct effect on adipose tissue, which is not secondary to catecholamine release.

Effects of Energy Drinks on Economy and Cardiovascular Measures

Peveler, WW, Sanders, GJ, Marczinski, CA, and Holmer, B. Effects of energy drinks on economy and cardiovascular measures. J Strength Cond Res 31(4): 882-887, 2017-The use of energy drinks among athletes has risen greatly. Caffeine and taurine are the 2 primary performance enhancing ingredients found in energy drinks. The number of emergency department visits involving energy drinks doubled over the past 5 years. Reviews of the health complications have highlighted adverse cardiovascular events. The literature reveals that caffeine is known to moderately increase blood pressure (BP) and heart rate (HR). The purpose of this study was to determine the effect of 3 different energy drinks on cardiovascular and performance measures. Fifteen recreational runners completed 5 trials. The first trial consisted of a graded exercise protocol. The 4 remaining trials consisted of 15-minute economy trials at a treadmill speed consistent with 70% of subject's V[Combining Dot Above]O2max. An hour before subjects ingested 1 of the 3 energy drinks or a placebo. HR, BP, V[Combining Dot Above]O2, and rating of perceived exertion (RPE) were recorded during the 15-minute trial. Mean values for dependent measures were compared using repeated-measures analysis of variance. Fifteen-minute systolic BP readings were significantly lower in the placebo trials (156.93 ± 15.50) in relation to the 3 energy drink trials (163.87 ± 13.30, 166.47 ± 13.71, and 165.00 ± 15.23). There were no significant differences in diastolic BP and HR. There were no significant differences found in V[Combining Dot Above]O2 or RPE measures. Ingestion of energy drinks demonstrated no change in V[Combining Dot Above]O2 or RPE during the economy trials. The findings show no performance benefits under the conditions of this study. However, there does appear to be a significant increase in systolic BP.

Multiple AMPK activators inhibit l-carnitine uptake in C2C12 skeletal muscle myotubes

Mutations in the gene that encodes the principal l-carnitine transporter, OCTN2, can lead to a reduced intracellular l-carnitine pool and the disease Primary Carnitine Deficiency. l-Carnitine supplementation is used therapeutically to increase intracellular l-carnitine. As AMPK and insulin regulate fat metabolism and substrate uptake, we hypothesized that AMPK-activating compounds and insulin would increase l-carnitine uptake in C2C12 myotubes. The cells express all three OCTN transporters at the mRNA level, and immunohistochemistry confirmed expression at the protein level. Contrary to our hypothesis, despite significant activation of PKB and 2DG uptake, insulin did not increase l-carnitine uptake at 100 nM. However, l-carnitine uptake was modestly increased at a dose of 150 nM insulin. A range of AMPK activators that increase intracellular calcium content [caffeine (10 mM, 5 mM, 1 mM, 0.5 mM), A23187 (10 μM)], inhibit mitochondrial function [sodium azide (75 μM), rotenone (1 μM), berberine (100 μM), DNP (500 μM)], or directly activate AMPK [AICAR (250 μM)] were assessed for their ability to regulate l-carnitine uptake. All compounds tested significantly inhibited l-carnitine uptake. Inhibition by caffeine was not dantrolene (10 μM) sensitive despite dantrolene inhibiting caffeine-mediated calcium release. Saturation curve analysis suggested that caffeine did not competitively inhibit l-carnitine transport. To assess the potential role of AMPK in this process, we assessed the ability of the AMPK inhibitor Compound C (10 μM) to rescue the effect of caffeine. Compound C offered a partial rescue of l-carnitine uptake with 0.5 mM caffeine, suggesting that AMPK may play a role in the inhibitory effects of caffeine. However, caffeine likely inhibits l-carnitine uptake by alternative mechanisms independently of calcium release. PKA activation or direct interference with transporter function may play a role.

[MUSCLE FATIGUE: FACTORS OF DEVELOPMENT AND WAYS OF CORRECTION]

The data regarding the analysis of the physiological and biochemical mechanisms of muscle fatigue and ways to prevent it are summarized. The effect of the most common endogenous and exogenous antioxidants in the biochemical processes in muscle fatigue was analyzed. It is shown that biocompatible, non-toxic water-soluble C(60) fullerenes, which possess powerful antioxidative properties, promise great prospects in the correction of skeletal muscle fatigue caused by the destructive action of free radicals.

Drug Use and Misuse in the Mountains: A UIAA MedCom Consensus Guide for Medical Professionals

Donegani, Enrico, Peter Paal, Thomas Küpper, Urs Hefti, Buddha Basnyat, Anna Carceller, Pierre Bouzat, Rianne van der Spek, and David Hillebrandt. Drug use and misuse in the mountains: a UIAA MedCom consensus guide for medical professionals. High Alt Med Biol. 17:157-184, 2016.-Aims: The aim of this review is to inform mountaineers about drugs commonly used in mountains. For many years, drugs have been used to enhance performance in mountaineering. It is the UIAA (International Climbing and Mountaineering Federation-Union International des Associations d'Alpinisme) Medcom's duty to protect mountaineers from possible harm caused by uninformed drug use. The UIAA Medcom assessed relevant articles in scientific literature and peer-reviewed studies, trials, observational studies, and case series to provide information for physicians on drugs commonly used in the mountain environment. Recommendations were graded according to criteria set by the American College of Chest Physicians.

RESULTS

Prophylactic, therapeutic, and recreational uses of drugs relevant to mountaineering are presented with an assessment of their risks and benefits.

CONCLUSIONS

If using drugs not regulated by the World Anti-Doping Agency (WADA), individuals have to determine their own personal standards for enjoyment, challenge, acceptable risk, and ethics. No system of drug testing could ever, or should ever, be policed for recreational climbers. Sponsored climbers or those who climb for status need to carefully consider both the medical and ethical implications if using drugs to aid performance. In some countries (e.g., Switzerland and Germany), administrative systems for mountaineering or medication control dictate a specific stance, but for most recreational mountaineers, any rules would be unenforceable and have to be a personal decision, but should take into account the current best evidence for risk, benefit, and sporting ethics.

Effect of Coffee Ingestion on Physiological Responses and Ratings of Perceived Exertion during Submaximal Endurance Exercise

This study examined the effect of coffee ingestion on physiological responses and ratings of perceived exertion (RPE) during submaximal endurance exercises by 10 healthy young adults. Participants performed a submaximal endurance cycling exercise corresponding to 60% of maximum oxygen uptake capacity for 60 min. They drank either caffeinated coffee with a caffeine content of 6 mg/kg body-mass of each participant (Caf) or a decaffeinated coffee (Dec) 60 min. before starting exercise. Participants participated in the blind design experiment under both conditions at a one-week interval. Oxygen uptake, respiratory exchange ratio, heart rate, RPE, and plasma lactate concentration were measured during the endurance exercise. The RPE under the Caffeinated coffee condition during the last 60 min. of endurance exercise was significantly lower than that in the Decaffeinated coffee condition. However, no significant differences in any physiological response were observed between conditions. Thus, caffeine ingestion 60 min. before starting exercise had an insignificant effect on the physiological responses, except for RPE during submaximal endurance exercises for 60 min. Caffeine ingestion before endurance exercise of relatively low intensity may have a beneficial effect on psychological responses.

Structure-Bioactivity Relationships of Methylxanthines: Trying to Make Sense of All the Promises and the Drawbacks

Methylxanthines are a group of phytochemicals derived from the purine base xanthine and obtained from plant secondary metabolism. They are unobtrusively included in daily diet in common products as coffee, tea, energetic drinks, or chocolate. Caffeine is by far the most studied methylxanthine either in animal or epidemiologic studies. Theophylline and theobromine are other relevant methylxanthines also commonly available in the aforementioned sources. There are many disseminated myths about methylxanthines but there is increased scientific knowledge to discuss all the controversy and promise shown by these intriguing phytochemicals. In fact, many beneficial physiologic outcomes have been suggested for methylxanthines in areas as important and diverse as neurodegenerative and respiratory diseases, diabetes or cancer. However, there have always been toxicity concerns with methylxanthine (over)consumption and pharmacologic applications. Herein, we explore the structure-bioactivity relationships to bring light those enumerated effects. The potential shown by methylxanthines in such a wide range of conditions should substantiate many other scientific endeavors that may highlight their adequacy as adjuvant therapy agents and may contribute to the advent of functional foods. Newly designed targeted molecules based on methylxanthine structure may originate more specific and effective outcomes.

Improvements in Cycling but Not Handcycling 10 km Time Trial Performance in Habitual Caffeine Users

Caffeine supplementation during whole-/lower-body exercise is well-researched, yet evidence of its effect during upper-body exercise is equivocal. The current study explored the effects of caffeine on cycling/handcycling 10 km time trial (TT) performance in habitual caffeine users. Eleven recreationally trained males (mean (SD) age 24 (4) years, body mass 85.1 (14.6) kg, cycling/handcycling peak oxygen uptake (V·_peak) 42.9 (7.3)/27.6 (5.1) mL∙kg∙min⁻¹, 160 (168) mg/day caffeine consumption) completed two maximal incremental tests and two familiarization sessions. During four subsequent visits, participants cycled/handcycled for 30 min at 65% mode-specific V·_peak (preload) followed by a 10 km TT following the ingestion of 4 mg∙kg⁻¹ caffeine (CAF) or placebo (PLA). Caffeine significantly improved cycling (2.0 (2.0)%; 16:35 vs. 16:56 min; p = 0.033) but not handcycling (1.8 (3.0)%; 24:10 vs. 24:36 min; p = 0.153) TT performance compared to PLA. The improvement during cycling can be attributed to the increased power output during the first and last 2 km during CAF. Higher blood lactate concentration (Bla) was reported during CAF compared to PLA (p < 0.007) and was evident 5 min post-TT during cycling (11.2 ± 2.6 and 8.8 ± 3.2 mmol/L; p = 0.001) and handcycling (10.6 ± 2.5 and 9.2 ± 2.9 mmol/L; p = 0.006). Lower overall ratings of perceived exertion (RPE) were seen following CAF during the preload (p < 0.05) but not post-TT. Lower peripheral RPE were reported at 20 min during cycling and at 30 min during handcycling, and lower central RPE was seen at 30 min during cycling (p < 0.05). Caffeine improved cycling but not handcycling TT performance. The lack of improvement during handcycling may be due to the smaller active muscle mass, elevated (Bla) and/or participants’ training status.

Effects of acute caffeine supplementation on reducing exercise-associated hypoglycaemia in individuals with Type 1 diabetes mellitus

AIM

To determine the effects of acute caffeine ingestion on glycaemia during moderate to vigorous intensity aerobic exercise and in recovery in individuals with Type 1 diabetes.

METHODS

A total of 13 patients with Type 1 diabetes [eight women, five men: mean ± sd age 25.9 ± 8.8 years, BMI 71.9 ± 11.0 kg, maximal oxygen consumption 46.6 ± 12.7 ml/kg/min, body fat 19.9 ± 7.2%, duration of diabetes 14.4 ± 10.1 years and HbA1c 55 ± 8 mmol/mol (7.4 ± 0.8%)] were recruited. Participants ingested capsules that contained gelatin or pure caffeine (6.0 mg/kg body mass) and performed afternoon exercise for 45 min at 60% maximal oxygen consumption on two separate visits with only circulating basal insulin levels.

RESULTS

The main finding was that a single caffeine dose attenuates the drop in glycaemia by 1.8 ± 2.8 mmol/l compared with placebo intake during exercise (P=0.056). Continuous glucose monitoring data, however, showed that caffeine was associated with elevated glycaemia at bedtime after exercise, compared with placebo, but lower glucose concentrations in the early morning the next day.

CONCLUSIONS

Caffeine intake should be considered as another strategy that may modestly attenuate hypoglycaemia in individuals with Type 1 diabetes during exercise, but should be taken with precautionary measures as it may increase the risk of late-onset hypoglycaemia.

Caffeine Affects Time to Exhaustion and Substrate Oxidation during Cycling at Maximal Lactate Steady State

This study analyzed the effects of caffeine intake on whole-body substrate metabolism and exercise tolerance during cycling by using a more individualized intensity for merging the subjects into homogeneous metabolic responses (the workload associated with the maximal lactate steady state—MLSS). MLSS was firstly determined in eight active males (25 ± 4 years, 176 ± 7 cm, 77 ± 11 kg) using from two to four constant-load tests of 30 min. On two following occasions, participants performed a test until exhaustion at the MLSS workload 1 h after taking either 6 mg/kg of body mass of caffeine or placebo (dextrose), in a randomized, double-blinded manner. Respiratory exchange ratio was calculated from gas exchange measurements. There was an improvement of 22.7% in time to exhaustion at MLSS workload following caffeine ingestion (95% confidence limits of ±10.3%, p = 0.002), which was accompanied by decrease in respiratory exchange ratio (p = 0.001). These results reinforce findings indicating that sparing of the endogenous carbohydrate stores could be one of the several physiological effects of caffeine during submaximal performance around 1 h.

Performance effects and metabolic consequences of caffeine and caffeinated energy drink consumption on glucose disposal

This review documents two opposing effects of caffeine and caffeine-containing energy drinks, i.e., their positive effects on athletic performance and their negative impacts on glucose tolerance in the sedentary state. Analysis of studies examining caffeine administration prior to performance-based exercise showed caffeine improved completion time by 3.6%. Similar analyses following consumption of caffeine-containing energy drinks yielded positive, but more varied, benefits, which were likely due to the diverse nature of the studies performed, the highly variable composition of the beverages consumed, and the range of caffeine doses administered. Conversely, analyses of studies administering caffeine prior to either an oral glucose tolerance test or insulin clamp showed a decline in whole-body glucose disposal of ~30%. The consequences of this resistance are unknown, but there may be implications for the development of a number of chronic diseases. Both caffeine-induced performance enhancement and insulin resistance converge with the primary actions of caffeine on skeletal muscle.

Caffeine ingestion after rapid weight loss in judo athletes reduces perceived effort and increases plasma lactate concentration without improving performance

The objective of this study was to examine the effect of caffeine on judo performance, perceived exertion, and plasma lactate response when ingested during recovery from a 5-day weight loss period. Six judokas performed two cycles of a 5-day rapid weight loss procedure to reduce their body weight by ~5%. After weigh-in, subjects re-fed and rehydrated over a 4-h recovery period. In the third hour of this "loading period", subjects ingested a capsule containing either caffeine (6 mg·kg-1) or placebo. One hour later, participants performed three bouts of a judo fitness test with 5-min recovery periods. Perceived exertion and plasma lactate were measured before and immediately after each test bout. Body weight was reduced in both caffeine and placebo conditions after the weight loss period (-3.9% ± 1.6% and -4.0% ± 2.3% from control, respectively, p < 0.05). At three hours after weigh-in, body weight had increased with both treatments but remained below the control (-3.0% ± 1.3% and -2.7% ± 2.2%). There were no significant differences in the number of throws between the control, caffeine or placebo groups. However, plasma lactate was systemically higher and perceived exertion lower in the subjects who ingested caffeine compared to either the control or placebo subjects (p < 0.05). In conclusion, caffeine did not improve performance during the judo fitness test after a 5-day weight loss period, but reduced perceived exertion and increased plasma lactate.

Differences between the nonselective adenosine receptor antagonists caffeine and theophylline in motor and mood effects: studies using medium to high doses in animal models

RATIONALE

Caffeine and theophylline are methylxanthines that are broadly consumed, sometimes at high doses, and act as minor psychostimulants. Both are nonselective adenosine antagonists for A1 and A2A receptors, which are colocalized with dopamine D1 and D2 receptors in striatal areas. Adenosine antagonists generally have opposite actions to those of dopamine antagonists. Although the effects of caffeine are widely known, theophylline has been much less well characterized, especially at high doses.

METHODS

Adult male CD1 mice were used to study the effect of a broad range of doses (25.0, 50.0 or 100.0mg/kg) of caffeine and theophylline on measures of spontaneous locomotion and coordination, as well as the pattern of c-Fos immunoreactivity in brain areas rich in adenosine and dopamine receptors. In addition, we evaluated possible anxiety and stress effects of these doses.

RESULTS

Caffeine, at these doses, impaired or suppressed locomotion in several paradigms. However, theophylline was less potent than caffeine at suppressing motor parameters, and even stimulated locomotion. Both drugs induced corticosterone release, however caffeine was more efficacious at intermediate doses. While caffeine showed an anxiogenic profile at all doses, theophylline only did so at the highest dose used (50mg/kg). Only theophylline increased c-Fos immunoreactivity in cortical areas.

CONCLUSION

Theophylline has fewer disruptive effects than caffeine on motor parameters and produces less stress and anxiety effects. These results are relevant for understanding the potential side effects of methylxanthines when consumed at high doses.

Likely additive ergogenic effects of combined preexercise dietary nitrate and caffeine ingestion in trained cyclists

Aims. To evaluate the possible additive effects of beetroot juice plus caffeine on exercise performance. Methods. In a randomized, double-blinded study design, fourteen healthy well-trained men aged 22 ± 3 years performed four trials on different occasions following preexercise ingestion of placebo (PLA), PLA plus 5 mg/kg caffeine (PLA+C), beetroot juice providing 8 mmol of nitrate (BR), and beetroot juice plus caffeine (BR+C). Participants cycled at 60% maximal oxygen uptake (V˙O2max) for 30 min followed by a time to exhaustion (TTE) trial at 80% V˙O2max. Saliva was collected before supplement ingestion, before exercise, and after the TTE trial for salivary nitrate, nitrite, and cortisol analysis. Results. In beetroot trials, saliva nitrate and nitrite increased >10-fold before exercise compared with preingestion (P ≤ 0.002). TTE in BR+C was 46% higher than in PLA (P = 0.096) and 18% and 27% nonsignificant TTE improvements were observed on BR+C compared with BR and PLA+C alone, respectively. Lower ratings of perceived exertion during TTE were found during 80% V˙O2max on BR+C compared with PLA and PLA+C (P < 0.05 for both). Conclusions. Acute preexercise beetroot juice coingestion with caffeine likely has additive effects on exercise performance compared with either beetroot or caffeine alone.

The effects of caffeine, nicotine, ethanol, and tetrahydrocannabinol on exercise performance

Caffeine, nicotine, ethanol and tetrahydrocannabinol (THC) are among the most prevalent and culturally accepted drugs in western society. For example, in Europe and North America up to 90% of the adult population drinks coffee daily and, although less prevalent, the other drugs are also used extensively by the population. Smoked tobacco, excessive alcohol consumption and marijuana (cannabis) smoking are addictive and exhibit adverse health effects. These drugs are not only common in the general population, but have also made their way into elite sports because of their purported performance-altering potential. Only one of the drugs (i.e., caffeine) has enough scientific evidence indicating an ergogenic effect. There is some preliminary evidence for nicotine as an ergogenic aid, but further study is required; cannabis and alcohol can exhibit ergogenic potential under specific circumstances but are in general believed to be ergolytic for sports performance. These drugs are currently (THC, ethanol) or have been (caffeine) on the prohibited list of the World Anti-Doping Agency or are being monitored (nicotine) due to their potential ergogenic or ergolytic effects. The aim of this brief review is to evaluate the effects of caffeine, nicotine, ethanol and THC by: 1) examining evidence supporting the ergogenic or ergolytic effects; 2) providing an overview of the mechanism(s) of action and physiological effects; and 3) where appropriate, reviewing their impact as performance-altering aids used in recreational and elite sports.

Caffeine and glucose homeostasis during rest and exercise in diabetes mellitus

Caffeine is a substance that has been used in our society for generations, primarily for its effects on the central nervous system that causes wakefulness. Caffeine supplementation has become increasingly more popular as an ergogenic aid for athletes and considerable scientific evidence supports its effectiveness. Because of their potential to alter energy metabolism, the effects of coffee and caffeine on glucose metabolism in diabetes have also been studied both epidemiologically and experimentally. Predominantly targeting the adenosine receptors, caffeine causes alterations in glucose homeostasis by decreasing glucose uptake into skeletal muscle, thereby causing elevations in blood glucose concentration. Caffeine intake has also been proposed to increase symptomatic warning signs of hypoglycemia in patients with type 1 diabetes and elevate blood glucose levels in patients with type 2 diabetes. Other effects include potential increases in glucose counterregulatory hormones such as epinephrine, which can also decrease peripheral glucose disposal. Despite these established physiological effects, increased coffee intake has been associated with reduced risk of developing type 2 diabetes in large-scale epidemiological studies. This review paper highlights the known effects of caffeine on glucose homeostasis and diabetes metabolism during rest and exercise.

The combination of theophylline and endothelin receptor antagonism improves exercise performance of rats under simulated high altitude

Decreased physical performance is a well-known consequence of rapid ascent to high altitude. Hypoxic pulmonary vasoconstriction (HPV) potentially limits cardiac output and systemic blood flow, thus preventing successful adaptation to rapid ascent. We hypothesized that pharmacological enhancement of the heart rate with theophylline, combined with reversal of HPV via endothelin blockade, could increase exercise performance at high altitude. Female Sprague-Dawley rats were treated with combinations of 1) theophylline, 2) the endothelin receptor antagonists sitaxsentan/ambrisentan, and/or 3) phosphodiesterase-5 inhibitor sildenafil and exposed to either a simulated high altitude (4,267 m) or 12% oxygen. Exercise capacity, peripheral blood flow, hemodynamics, and pulmonary leak were examined. Combination treatment with theophylline and endothelin blockade, but not with the respective single compounds, significantly prolonged run-to-fatigue time under simulated high altitude. No such efficacy was found when theophylline was combined with sildenafil. Neither theophylline nor sitaxsentan or their combination influenced breathing rates and hemoglobin oxygen saturation. Whereas under hypoxia, theophylline significantly increased muscular blood flow, and sitaxsentan increased tissue oxygenation, the combination improved both parameters but in a reduced manner. Under hypoxia, the combination treatment but not the single compounds significantly enhanced pulmonary arterial pressure compared with controls (13.1 ± 6.3 vs. 11.9 ± 5.2 mmHg), whereas mean arterial pressure remained unaffected. Pulmonary wet-to-dry weight ratios were unaffected by combination treatment. We conclude that concomitant dosing with a cardiac stimulant and endothelin antagonist can partially reverse loss of physical performance capacity under hypobaric hypoxia, independent from improving blood oxygen saturation.

Independent and combined effects of carbohydrate and caffeine ingestion on aerobic cycling performance in the fed state

The purpose of this study was to examine the independent and combined effects of carbohydrate and caffeine ingestion on performance and various physiological parameters during aerobic cycling (∼1 h). Ten male cyclists (28 ± 9 years, 73 ± 6 kg, 66 ± 9 mL·kg(-1)·min(-1) maximal oxygen consumption) performed 20 min of steady-state (SS) cycling (60% peak power (W(max))) followed by a simulated 20-km time trial (TT) under placebo (PLA), carbohydrate (CHO), caffeine (CAF), and combined CAF-CHO conditions, all of which were performed in the fed state. CAF-CHO improved TT performance by 3.4% ± 2% (84 ± 57 s) compared with PLA (p < 0.05), whereas no differences were detected among CHO, CAF, and PLA. The SS respiratory exchange ratio was elevated in CHO (0.92 ± 0.03), CAF (0.96 ± 0.07), and CAF-CHO (0.95 ± 0.02) compared with PLA (0.89 ± 0.03) (p < 0.05). Post-SS and post-TT blood glucose levels were also elevated in CAF-CHO (88.3 ± 16.7 mg·dL(-1) and 111.2 ± 33.5 mg·dL(-1), respectively) compared with PLA (74.5 ± 9.8 mg·dL(-1) and 85.4 ± 17.6 mg·dL(-1), respectively) (p < 0.05). Treatment conditions did not differentially impact SS pulmonary ventilation, oxygen consumption, heart rate, peak quadriceps muscle strength, rating of perceived exertion, or blood lactate. CAF and CHO improved TT performance when taken together but not independently. Although the present work did not yield any definitive physiological mechanisms for the performance findings, these data suggest that cyclists in the fed state should ingest carbohydrate and caffeine together to improve time trial performance.

Acute effects of a caffeine-containing supplement on bench press and leg extension strength and time to exhaustion during cycle ergometry

The purpose of the present study was to examine the acute effects of a caffeine-containing supplement (SUPP) on 1 repetition maximum (1RM) bench press and leg extension strength, as well as time to exhaustion (TTE), during cycle ergometry at a power output that corresponded to 80% of VO2peak. The study used a double-blinded, placebo-controlled, crossover design. Twenty-one untrained men (mean +/- SD age = 23.0 +/- 2.6 yr) were randomly assigned to take either the SUPP or placebo (PLAC) first. The SUPP contained 400 mg of caffeine, 66.7 mg of capsicum extract, 10 mg of bioperine, and 40 mg of niacin, and the PLAC was microcrystalline cellulose. Sixty minutes after taking either the SUPP or PLAC, the subjects were tested for 1RM bench press and leg extension strength, as well as TTE. After 1 week of rest, the subjects ingested the opposite substance (SUPP or PLAC) and were retested for 1RM bench press and leg extension strength, as well as TTE. The results indicated that the SUPP had no effect on 1RM bench press strength, 1RM leg extension strength, or TTE at 80% VO2peak. These findings did not support the use of the caffeine-containing SUPP in the present study as an ergogenic aid in untrained individuals.

International society of sports nutrition position stand: caffeine and performance

Position Statement: The position of The Society regarding caffeine supplementation and sport performance is summarized by the following seven points: 1.) Caffeine is effective for enhancing sport performance in trained athletes when consumed in low-to-moderate dosages (~3-6 mg/kg) and overall does not result in further enhancement in performance when consumed in higher dosages (≥ 9 mg/kg). 2.) Caffeine exerts a greater ergogenic effect when consumed in an anhydrous state as compared to coffee. 3.) It has been shown that caffeine can enhance vigilance during bouts of extended exhaustive exercise, as well as periods of sustained sleep deprivation. 4.) Caffeine is ergogenic for sustained maximal endurance exercise, and has been shown to be highly effective for time-trial performance. 5.) Caffeine supplementation is beneficial for high-intensity exercise, including team sports such as soccer and rugby, both of which are categorized by intermittent activity within a period of prolonged duration. 6.) The literature is equivocal when considering the effects of caffeine supplementation on strength-power performance, and additional research in this area is warranted. 7.) The scientific literature does not support caffeine-induced diuresis during exercise, or any harmful change in fluid balance that would negatively affect performance.

The effects of caffeine on ventilation and pulmonary function during exercise: an often-overlooked response

The effects of caffeine on exercise performance have been well documented, with most reviews focusing on the metabolic, hormonal, and/or central nervous system effects. However, caffeine's effects on ventilation and pulmonary function are often overlooked. Studies have shown that caffeine is a strong ventilatory stimulant, increasing the sensitivity of the peripheral chemoreceptors in untrained subjects and increasing exercise ventilation at all workloads in highly trained endurance athletes. The consequences of increased exercise ventilation could hold either positive or negative effects for exercise performance. Anti-inflammatory and bronchoprotective effects of caffeine are great enough to consider its efficacy as a possible prophylactic antiasthma treatment. Although an upper urinary concentration limit exists for caffeine with international sports doping control agencies, caffeine's universal accessibility in the marketplace has resulted in its daily use being increasingly more socially acceptable as an ergogenic substance for sport and exercise.

Effect of sugar-free Red Bull energy drink on high-intensity run time-to-exhaustion in young adults

Consuming sugar-free Red Bull energy drink before exercise has become increasingly popular among exercising individuals. The main purported active ingredient in sugar-free Red Bull is caffeine, which has been shown to increase aerobic exercise performance. The purpose of this study was to determine the effects of sugar-free Red Bull energy drink on high-intensity run time-to-exhaustion in young adults. Physically active university students (n = 17, 9 men, 8 woman; 21 +/- 4 years, 73.4 +/- 3.1 kg, 175.1 +/- 3.2 cm) participated in a double-blind, crossover, repeated-measures study where they were randomized to supplement with sugar-free Red Bull (2 mg x kg(-1) body mass caffeine or approximately 147 mg caffeine; 4 kcal/250 mL) and noncaffeinated, sugar-free placebo (lemon-lime flavored soft drink, tonic water, lime juice; 4 kcal/250 mL) separated by 7 days. Exercise capacity was assessed by a run time-to-exhaustion test at 80% Vo2max, perceived exertion was assessed immediately after exercise, and blood lactate was measured before and after exercise. There were no differences in run time-to-exhaustion (Red Bull: 12.6 +/- 3.8 minutes, placebo: 11.8 +/- 3.4 minutes), perceived exertion (Red Bull: 17.1 +/- 2.0, placebo: 16.6 +/- 1.8), or blood lactate between groups. In conclusion, sugar-free Red Bull energy drink did not influence high-intensity run time-to-exhaustion in young adults.