‏‏‎ ‎

‏‏‎ ‎

‏‏‎ ‎

During a marathon, the energy that fuels every movement and breath we take comes from the foods we consume. However, not all energy sources are equal. Let's explore the science behind the two main fuels our body uses for training and racing: carbohydrates and fats.
 

Carbohydrates: The body's preferred fuel
When we eat carbohydrates, they are broken down into simpler sugars such as glucose. This glucose provides us with immediate energy by entering our bloodstream, or it is stored in our liver and muscles as glycogen. During high-intensity activities, our body prioritizes the use of these glycogen stores. Why? Because glycogen can be rapidly broken down anaerobically to produce ATP (adenosine triphosphate), which meets the immediate energy demands of strenuous activities. However, our glycogen reserves are limited. Once they are depleted, our performance will decrease, leading to the undesirable phenomenon "hitting the wall" or "bonking". To prevent glycogen depletion, you can employ strategies such as carbohydrate loading in the days leading up to a race and consuming easily digestible carbohydrates during the event itself.

Fats: a slow energy source
Fats are stored as triglycerides in adipose tissues and can provide a significant amount of energy, which is highly beneficial during prolonged physical activities. When the body runs out of carbohydrate stores, it starts using fats to produce ATP. Although the process of breaking down fats to produce energy is slower than glycogen breakdown, it releases more energy per gram of fat, thus ensuring a sustained energy output. The challenge lies in training the body to efficiently tap into these fat reserves, especially during the later stages of long-duration events. Fat metabolism becomes increasingly significant at moderate intensities, where aerobic conditions allow for the sustained oxidation of fat, a process that becomes even more crucial as glycogen stores wane.

How heart rate dictates energy/fuel use
The body's choice of fuel is closely linked to heart rate, which acts as a proxy for exercise intensity. As heart rate and exercise intensity increase, the body gradually shifts to relying more on carbohydrates. This change occurs because the body needs rapid energy production that fats cannot supply quickly enough. When exercise intensity reaches a point where the demand for ATP outstrips the oxygen available, usually above 70-80% of the maximum heart rate, the body increasingly depends on anaerobic metabolism, which primarily uses carbohydrates. 

 

Glycogen, which is stored in the muscles and liver, becomes the primary source of energy because it can be broken down into glucose without the need for oxygen, providing quick bursts of energy. However, since glycogen stores are limited, a higher reliance on this energy pathway can lead to quicker depletion, resulting in fatigue and decreased performance - often experienced by athletes as 'hitting the wall'. 

 

This relationship between heart rate and energy source is why endurance athletes often train at different heart rate zones to improve their body's ability to oxidize fats and save glycogen, delaying or even preventing the onset of fatigue. Such training can help in 'teaching' the body to become more efficient at fat metabolism, even at slightly higher intensities, which is beneficial for long-duration sports where preserving carbohydrates as long as possible is advantageous. How your heart rate behaves throughout a marathon depends on several factors, such as dehydration and loss of blood plasma volume, increased body temperature, the build-up of metabolic byproducts, and fuel shifts. This gradual increase in heart rate over time, known as 'cardiac drift,' can subtly shift fuel usage from fats back towards carbohydrates, influencing nutrition and hydration strategies. So, as your heart rate increases, your preferred fuel source shifts as well. 

 

Understanding the interplay between carbohydrates and fats during a marathon is crucial, as it informs our nutrition strategy, ensuring we have a steady energy supply and can adapt as the race progresses and our body's demands shift.

Hydration, while crucial, is frequently overlooked in fueling strategies for endurance sports. It's vital not only for maintaining fluid balance but also for facilitating nutrient transport, including carbohydrates, and supporting key physiological processes. It is not just about regulating your fluid balance, but it also plays an important role in the transportation and absorption of carbohydrates, gastric emptying, heart rate, and metabolism. Simply focusing on carbohydrates is not enough. Therefore, we want to highlight the significance of hydration and sodium. 

 

Approximately 60% of the human body is water, with its distribution varying across different tissues. Next we'll explore how water and electrolytes, vital for numerous bodily functions, interact to maintain performance.

 

Minerals are naturally occurring inorganic solids present in small amounts in the diet. When dissolved in water, they either have a positive or negative charge, depending on the type of mineral, and are called electrolytes. Electrolytes can be acids, bases, or salts and occur in the body in extracellular or intracellular fluids. Electrolytes have multiple functions in the body due to their electrical charge, and an imbalance in electrolyte concentration disturbs homeostasis. 

 

One of the primary functions of electrolytes is to regulate fluid levels. In the body, most membranes are semipermeable, meaning water can diffuse across the membrane, but the molecules dissolved in water cannot without the use of transporters. When a solution is divided into two compartments with a semipermeable membrane, such as the intracellular and extracellular spaces, only water can move over the membrane to establish an equilibrium between the two compartments. Concentration gradients and hydrostatic pressure both influence the water balance. Hydrostatic pressure is created by the difference in water volume percentages between cells and blood plasma. 

 

Besides regulating fluid levels, electrolytes are essential in transmitting nerve signals, muscle contraction, regulating blood pH, and macronutrient absorption (such as carbohydrates) in the small intestine.

Hydration
Water is vital for various physiological functions, including nutrient transport, body temperature regulation, and cellular structure. When you exercise intensely, your body generates heat that must be dissipated to maintain balance. The primary way your body loses heat is through sweating, which is affected by environmental factors such as humidity and wind. Inadequate heat loss can result in hyperthermia or heatstroke. Sweat not only cools your body but also causes fluid and electrolyte loss, which can affect your performance. Dehydration can reduce skin blood flow and sweating rate, making it difficult to cool your body. Even a 2% decrease in body weight due to fluid loss can lead to symptoms such as decreased alertness and performance. Electrolyte loss, especially sodium and chloride, can disrupt cellular function and cause muscle cramps. 

 

Your body doesn't naturally compensate for fluid and electrolyte loss during sweating, so you need to replenish them before, during, and after your run. You can estimate your sweat rates by measuring body weight changes before and after exercise and taking into account fluid intake and urine output. 

 

Drinks for hydration are classified as hypertonic (high sugar and salt concentration), isotonic (similar to blood), or hypotonic (lower than blood). Isotonic drinks are absorbed faster. Overconsumption of hypotonic drinks, in particular, can result in hyponatremia, a dilution of blood sodium, with symptoms that mimic dehydration. To restore electrolyte balance and prevent hyponatremia, it is recommended to consume isotonic or hypertonic drinks. Pre-exercise drinks with added sodium can increase plasma volume and performance, particularly in moderately trained individuals. During exercise, drinks should contain around 20-30 mmol/L sodium to replace losses and maintain taste. Post-exercise drinks should be 150% of total fluid loss to compensate for urinary losses, with a similar sodium content to during-exercise drinks to facilitate rapid fluid and electrolyte balance restoration.

Sodium

Sodium is a positively charged ion that is mainly present in the extracellular fluid. It plays an important role in regulating extracellular fluid volume and blood pressure, which are essential for the transport of substrates and the excitability of nerve and muscle cells. Electrolytes move from inside to outside the cell and vice versa, which is necessary to transfer the signal over a nerve. Nerve conduction is crucial not only in the brain but also for muscle cells to contract and relax.

 

Additionally, sodium helps maintain cellular homeostasis (maintaining internal cell balance - important because it ensures cells can perform essential functions such as nutrient absorption, energy production, waste elimination, and more) and water balance. A high sodium concentration increases water absorption in the gut and reabsorption in the kidney. There is a potential link between sodium loss and muscle cramps, so it is important for athletes suffering from cramps to consume enough salts. For physical activity shorter than two hours, it is recommended to consume an isotonic drink (0.5-0.7 g/L Na+). Training or racing for more than two hours should include sodium (0.7-1 g/L of water) in their drink to increase palatability, promote fluid retention, and prevent hyponatremia. For ultra-endurance exercise, it is recommended that the sodium concentration of beverages is around 1.7 to 2.9 g/L. 

In short
To achieve endurance during a marathon, it's important to maintain a proper balance of hydration, sodium, and carbohydrates. This trio forms the foundation of your fueling strategy. Hydration is important for nutrient transport and thermal regulation, but it's closely linked to sodium as well. Sodium helps with fluid balance, nerve function, and muscle contraction, making it crucial for optimal absorption of water and carbohydrates. Carbohydrates are a well-established energy source, but efficient uptake is dependent on proper balance of fluids and electrolytes. Drinking isotonic solutions can help with carbohydrate absorption, providing a steady stream of energy while also optimising fluid uptake and reducing gastrointestinal discomfort. This balanced approach ensures that each component (water, sodium, and carbohydrates) is utilized effectively, boosting endurance, maintaining electrolyte balance, and preventing dehydration and hyponatremia. You should tailor your intake strategy to maintain this delicate balance, especially during long events where the risk of imbalance is higher.

Endurance athletes are well acquainted with the concept of "bonking" or "hitting the wall." It refers to a moment during prolonged, high-intensity exercise when the body's quick-access energy currency, known as glycogen reserves, run very low. These reserves typically fuel two-ish hours of  activity, and the intensity of the exertion and pre-existing glycogen levels determine the exact duration. Somewhere between the 25 and 32k mark is often when this energy crisis occurs, and it's a critical juncture where your body's demand for rapid energy conversion outpaces its dwindling glycogen supply. 

 

To avoid this decline and extend performance boundaries, strategic carbohydrate consumption before and during your training and/or race is essential. Unlike fats, which the body has in ample supply, carbohydrates are a limited resource. Therefore, they require careful management for endurance pursuits. As a result, nutritional strategies for endurance sports primarily focus on maximising carbohydrate availability. This ensures that these vital stores are replenished and readily accessible when starting the race. This preparation enables you to maintain your desired pace deeper into the race, pushing back the physiological limits and averting the onset of fatigue.

Carb loading is a strategy used to optimise your glycogen reserves before a race. The method involves a high intake of carbohydrates (typically 10 to 12 grams per kilogram of body weight) during the 3 to 4 days before the race. For instance, an athlete weighing 70 kilograms would need to consume 700 to 840 grams of carbohydrates daily. 

 

To supplement this, you should reduce training intensity to allow the muscles to saturate with glycogen without complex loading protocols. Carb-loading may increase overall body weight due to additional glycogen (three parts water for every part of glycogen) but the benefits of enhanced energy stores and hydration outweigh any potential drawbacks. 

 

You should consume high-carb foods such as rice, pasta, cereals, and sweet spreads while avoiding high-fat and high-fibre options. The goal is to maintain a tasty and familiar diet that encourages the consumption of the necessary volume of food without leading to overindulgence. Incorporating carbohydrate-dense liquids like high-energy drinks or gels can further contribute to achieving carb-loading goals without contributing to fullness. Fibre is a non-digestible carbohydrate that could add unnecessary weight and affect race-day agility. Therefore, you should go for low-fibre options during this time. 

On the big day, breakfast plays a crucial role in providing sustained energy levels. The timing of your breakfast is essential to balance with adequate rest, especially when the marathon has a varied start time. When you wake up on race day, your body's liver glycogen, which fuels vital functions overnight, is quite low and requires replenishing to prevent hypoglycemia. 

 

To fuel your body in the morning, consume between 100 to 200 grams of carbohydrates within the 3 to 4-hour window before the race. Instead of having a single large meal, divide your carbohydrate intake across several smaller snacks or carbohydrate-rich drinks. This strategy caters to those who may find it challenging to eat a full meal due to pre-race nerves or digestive concerns. 

 

When choosing your pre-race food, go for items that are low in fat, fiber, and protein, as these can slow down the digestive process and cause gastrointestinal distress during the race. Dairy is often well-tolerated, but those sensitive to lactose may need to limit their intake on race morning. Your breakfast should consist of carbohydrate-rich foods like cereals, white bread, jam, honey, pancakes, and fruit juices. 

Caffeine is known for its ability to boost mental focus and reduce the feeling of exhaustion during intense physical activity. It works by blocking adenosine, a molecule that signals fatigue, leading to an increase in neuron activity and a sense of alertness. 

 

Athletes often use caffeine to enhance their performance, and it's recommended to take a moderate dose of 2 to 3 mg per kilogram of body weight, around 30 to 60 minutes before the activity. For example, a 70 kg person should consume around 140 to 210 mg of caffeine. 

 

Caffeine has several benefits, including mobilising fatty acids, enhancing muscle contraction, and triggering the release of endorphins that help reduce pain and potentially prolong endurance. 

 

While caffeine can cause dehydration when taken in large quantities (this is often exaggerated), maintaining proper hydration is still crucial, especially if you choose a caffeinated beverage that contains diuretics. Keeping a balance between fluid intake and caffeine consumption can help sustain energy levels without leading to dehydration. 

 

In summary, caffeine is a useful tool for athletes when used strategically alongside proper hydration, carbohydrate intake, and attention to individual tolerances. As each runner crosses the finish line, the elation felt may be a testament to the strategic interplay of caffeine, discipline, and the sheer will to outpace fatigue. 

 

We recommend taking 01 Before 30 minutes before the race to optimise its effects.

Now, the million dollar question: What to use during the race itself...? Well, as said, it's important to consume enough carbohydrates per hour during a race as they provide several advantages such as more energy, improved performance, and faster finishing times. Carbs are the best fuel source for athletes, so it's important to focus on them rather than other macro-nutrients. However, the amount of carbs you should consume per hour depends on various factors like the intensity of the race. If you're aiming to finish the race, 30-60 grams per hour should suffice (one 02 During gel or drink mix per hour). On the other hand, if you're running at a higher pace/intensity, you should consume 90 grams of carbs per hour, which equates to (just) two units of 02 During. A recommended approach is to consume one 02 During drink mix over the hour and a 02 During gel halfway into the hour. 

 

It's important to be selective when it comes to choosing gels or drink mixes. Avoid any products that use a single source of carbohydrates such as maltodextrin, glucose, or fructose, or primarily use just one of these carbs. These can cause gut issues or gastrointestinal (GI) problems. Instead, opt for a balanced mix of two or three carb sources and aim for a carb ratio of 2:1 or 2:1:1.5. This will make it easier for your gut to process these carbs, resulting in faster gastric emptying (energy availability) and fewer GI/gut issues.

 

So, in summary, and depending on your training/race intensity:

 

Low-intensity or sub-2-hour training sessions or race: 1 x 02 During (drink or gel) per hour

High-intensity or super-2-hour training sessions or race: 2 x 02 During (one drink and one gel) per hour

We talked about this in a previous blog, but we can’t stress it enough. Training your body to consume large amounts of carbohydrates per hour is crucial if you plan to use carbs as your primary fuel source during a race, such as a marathon. It is essential to consistently use them during your weekly runs, rides, or workouts. Also, it is not wise to switch brands or suddenly increase your hourly intake on race day. Do. Not. Do. That. Your body is already under significant stress during the race, and overloading or stressing your system can be harmful. This is why the off-season is the perfect time to read up, try new brands and products, and train your system to get used to specific carb ratios, formats (such as gels, drinks, bars), and quantities you intend to use during the race.

Use them for water or cooling, but best avoid the sports drinks they offer as they’re not the products you trained with. They may also offer (carbonated) products that are high in fat, protein or fibres, and you best avoid those. So, bring what you trained with and plan ahead.

We developed 02 During in response to an extremely confusing and broad offering of gels and drink mixes already available.  Despite the clear science and available information, many products still contain sub-optimal carb ratios and confusing quantities, making it difficult for athletes to optimize their energy management. How can we be expected to consume 90-135 grams per hour when gels typically contain between 18-25 grams of carbohydrates each, especially when such a low-carb gel costs around €2,00-3,50 per unit? This makes things too expensive and highly impractical for most—not to mention the challenge of carrying all those gels.

Both our 02 During drink mix and gel contain 45 grams of carbs per serving, simplifying intake planning and energy management optimisation while significantly reducing cost per hour/training - even when aiming for 135 g/h. 

To help you further, we've put together a comprehensive fuel and hydration guide. If you're interested in getting a personalised intake plan, just follow the link below, answer a few questions, and our performance coaches will tailor a plan for you.

Academy of Nutrition and Dietetics, Dietitians of Canada, & American College of Sport Medicine. (2016). Nutrition and Athletic Performance. Medicine and Science in Sports and Exercise, 48(3), 543–568. https://doi.org/10.1249/MSS.0000000000000852 

Achten, J., & Jeukendrup, A. E. (2004). Optimizing fat oxidation through exercise and diet. Nutrition, 20(7–8), 716–727. https://doi.org/10.1016/j.nut.2004.04.005 

Ahmed, E. M. (2015). Hydrogel: Preparation, characterization, and applications: A review. Journal of Advanced Research, 6(2), 105–121. https://doi.org/10.1016/j.jare.2013.07.006 

Andres, S., Ziegenhagen, R., Trefflich, I., Pevny, S., Schultrich, K., Braun, H., Schänzer, W., Hirsch-Ernst, K. I., Schäfer, B., & Lampen, A. (2017). Creatine and creatine forms intended for sports nutrition. In Molecular Nutrition and Food Research (Vol. 61, Issue 6, p. 1600772). Wiley-VCH Verlag. https://doi.org/10.1002/mnfr.201600772 

Aoi, W., & Marunaka, Y. (2014). Importance of pH Homeostasis in Metabolic Health and Diseases: Crucial Role of Membrane Proton Transport. BioMed Research International, 2014. https://doi.org/10.1155/2014/598986 

Apostu, M. (2014). A Strategy for Maintaining Fluid and Electrolyte Balance in Aerobic Effort. Procedia - Social and Behavioral Sciences, 117, 323–328. https://doi.org/10.1016/j.sbspro.2014.02.221 

Areta, J. L., Burke, L. M., Ross, M. L., Camera, D. M., West, D. W. D., Broad, E. M., Jeacocke, N. A., Moore, D. R., Stellingwerff, T., Phillips, S. M., Hawley, J. A., & Coffey, V. G. (2013). Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. Journal of Physiology, 591(9), 2319–2331. https://doi.org/10.1113/jphysiol.2012.244897 

Atletiekunie. (2020, September 30). Running fuel; Energygel of isotone sportdrank? Hardlopen.Nl. https://www.hardlopen.nl/artikelen/voeding/running-fuel-energygel-of-isotone-sportdrank/ 

Australian Institute of Sports. (2021). AIS SPORTS SUPPLEMENT FRAMEWORK CREATINE MONOHYDRATE. www.sportintegrity.gov.au/what-we-do/anti-doping/supplements-sport 

Ayhan, H., Erdo.an, M. Ö., Yi.it, Y., Gencer, E. G., Turan, R. .., Akyol, N. K., & Karakum, M. (2014). The Reliability of Blood Gas Electrolytes. JAEM, 13, 49–52. https://doi.org/10.5152/jaem.2014.06978 

Baker, L. B., & Jeukendrup, A. E. (2014). Optimal Composition of Fluid-Replacement Beverages. Compr Physiol, 4, 575–620. https://doi.org/10.1002/cphy.c130014 

Baker, L. B., Lang, J. A., & Kenney, W. L. (2008). Quantitative analysis of serum sodium concentration after prolonged running in the heat. Journal of Applied Physiology, 105(1), 91–99. https://doi.org/10.1152/japplphysiol.00130.2008 

Baker, L. B., Nuccio, R. P., & Jeukendrup, A. E. (2014). Acute effects of dietary constituents on motor skill and cognitive performance in athletes. Nutrition Reviews, 72(12), 790–802. https://doi.org/10.1111/nure.12157 

Balsom, P., Gaitanos, G. C., Söderlund, K., & Ekblom, B. (1999). High-intensity exercise and muscle glycogen availability in humans. Article in Acta Physiologica Scandinavica, 165, 337–345. https://doi.org/10.1046/j.1365-201x.1999.00517.x 

Baur, D. A., & Saunders, M. J. (2021). Carbohydrate supplementation: a critical review of recent 

innovations. European Journal of Applied Physiology, 121(1), 23–66. https://doi.org/10.1007/s00421-020-04534-y 

Bender, D. A., & Cunningham, S. M. C. (2021). Introduction to Nutrition and Metabolism. In Introduction to Nutrition and Metabolism (6th ed.). CRC Press. https://doi.org/10.1201/9781003139157 

Blancquaert, L., Everaert, I., & Derave, W. (2015). Beta-alanine supplementation, muscle carnosine and exercise performance. Current Opinion in Clinical Nutrition and Metabolic Care, 18(1), 63–70. https://doi.org/10.1097/MCO.0000000000000127 

Boeije, H. R. (2010). Analysis in Qualitative Research (1st ed.). SAGE. 

Bogdanis, G. C., Nevill, M. E., Boobis, L. H., & Lakomy, H. K. A. (1996). Contribution of phosphocreatine and aerobic metabolism to energy supply during repeated sprint exercise. Journal of Applied Physiology, 80(3), 876–884. https://doi.org/10.1152/jappl.1996.80.3.876 

Booth, F. W., Ruegsegger, G. N., Toedebusch, R. G., & Yan, Z. (2015). Endurance Exercise and the Regulation of Skeletal Muscle Metabolism. Progress in Molecular Biology and Translational Science, 135, 129–151. https://doi.org/10.1016/bs.pmbts.2015.07.016 

Bowtell, J., & Kelly, · Vincent. (2019). Fruit-Derived Polyphenol Supplementation for Athlete Recovery and Performance. Sports Medicine, 49(1), 3–23. https://doi.org/10.1007/s40279-018-0998-x 

Brigelius.Flohé, R., & Traber, M. G. (1999). Vitamin E: function and metabolism. The FASEB Journal, 13(10), 1145–1155. https://doi.org/10.1096/fasebj.13.10.1145 

Brown, S. (2010). Likert Scale Examples for Surveys. 

Bucci, L. (1993). Nutrients as Ergogenic Aids for Sports and Exercise. In Nutrients as Ergogenic Aids for Sports and Exercise (1st ed.). CRC Press. https://doi.org/10.1201/9781003068051 

Buford, T. W., Kreider, R. B., Stout, J. R., Greenwood, M., Campbell, B., Spano, M., Ziegenfuss, T., Lopez, H., Landis, J., & Antonio, J. (2007). International Society of Sports Nutrition position stand: Creatine supplementation and exercise. Journal of the International Society of Sports Nutrition, 4(1), 1–8. https://doi.org/10.1186/1550-2783-4-6 

Campbell, C., Prince, D., Braun, M., Applegate, E., & Casazza, G. A. (2008). Carbohydrate-supplement form and exercise performance. International Journal of Sport Nutrition and Exercise Metabolism, 18(2), 179–190. https://doi.org/10.1123/ijsnem.18.2.179 

Cannell, J. J., Hollis, B. W., Sorenson, M. B., Taft, T. N., & B Anderson, J. J. (2009). Athletic Performance and Vitamin D. Med. Sci. Sports Exerc, 41(5), 1102–1110. https://doi.org/10.1249/MSS.0b013e3181930c2b 

Carr, A. C., & Maggini, S. (2017). Vitamin C and immune function. Nutrients, 9(11), 1211. https://doi.org/10.3390/nu9111211 

Carr, A. J., Hopkins, W. G., & Gore, C. J. (2011). Effects of acute alkalosis and acidosis on performance: A meta-analysis. Sports Medicine, 41(10), 801–814. https://doi.org/10.2165/11591440- 000000000-00000 

Casey, A., Constantin-Teodosiu, D., Howell, S., Hultman, E., & Greenhaff, P. L. (1996). Metabolic response of type I and II muscle fibers during repeated bouts of maximal exercise in humans. American Journal of Physiology - Endocrinology and Metabolism, 271(1 34-1). https://doi.org/10.1152/ajpendo.1996.271.1.e38 

Castelfranco, A. M., & Hartline, D. K. (2016). Evolution of rapid nerve conduction. Brain Research, 1641, 11–33. https://doi.org/10.1016/j.brainres.2016.02.015 

Coles, M. G., & Luetkemeier, M. J. (2005). Sodium-facilitated hypervolemia, endurance performance, and thermoregulation. International Journal of Sports Medicine, 26(3), 182–187. https://doi.org/10.1055/s-2004-820989 

Coyle, E. F. (2004). Fluid and fuel intake during exercise. Journal of Sports Sciences, 22(1), 39–55. https://doi.org/10.1080/0264041031000140545 

Darwish, A., & Lui, F. (2019). Physiology, Colloid Osmotic Pressure. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/pubmed/31082111 

de Oliveira, E. P., & Burini, R. C. (2014). Carbohydrate-dependent, exercise-induced gastrointestinal distress. Nutrients, 6(10), 4191–4199. https://doi.org/10.3390/nu6104191 

Dearlove, D. J., Harrison, O. K., Hodson, L., Jefferson, A., Clarke, K., & Cox, P. J. (2021). The Effect of Blood Ketone Concentration and Exercise Intensity on Exogenous Ketone Oxidation Rates in Athletes. Medicine and Science in Sports and Exercise, 53(3), 505–516. https://doi.org/10.1249/MSS.0000000000002502 

Doherty, M., & Smith, P. M. (2005). Effects of caffeine ingestion on rating of perceived exertion during and after exercise: A meta-analysis. Scandinavian Journal of Medicine and Science in Sports, 15(2), 69–78. https://doi.org/10.1111/j.1600-0838.2005.00445.x 

Dolan, E., Swinton, P. A., Painelli, V. D. S., Hemingway, B. S., Mazzolani, B., Smaira, F. I., Saunders, B., Artioli, G. G., & Gualano, B. (2019). A Systematic Risk Assessment and Meta-Analysis on the Use
 of Oral .-Alanine Supplementation. Advances in Nutrition, 10(3), 452–463. https://doi.org/10.1093/advances/nmy115 

Dong, O., & Wiltshire, T. (2019). Electrolytes. In Principles of Nutrigenetics and Nutrigenomics: Fundamentals of Individualized Nutrition (pp. 309–315). Elsevier. https://doi.org/10.1016/B978- 0-12-804572-5.00041-0 

Elejalde, E., Villarán, M. C., & Alonso, R. M. (2021). Grape polyphenols supplementation for exercise- induced oxidative stress. Journal of the International Society of Sports Nutrition, 18(1), 1–12. https://doi.org/10.1186/s12970-020-00395-0 

Etikan, I. (2016). Comparison of Convenience Sampling and Purposive Sampling. American Journal of Theoretical and Applied Statistics, 5(1), 1. https://doi.org/10.11648/j.ajtas.20160501.11 

European Food Safety Authority. (2017). Dietary Reference Values for nutrients Summary report. EFSA Supporting Publications, 14(12). https://doi.org/10.2903/sp.efsa.2017.e15121 

Evans, G. H., James, L. J., Shirreffs, S. M., & Maughan, R. J. (2017). Optimizing the restoration and maintenance of fluid balance after exercise-induced dehydration. Journal of Applied Physiology, 122(4), 945–951. https://doi.org/10.1152/japplphysiol.00745.2016 

Garthe, I., & Maughan, R. J. (2018). Athletes and supplements: Prevalence and perspectives. In International Journal of Sport Nutrition and Exercise Metabolism (Vol. 28, Issue 2, pp. 126–138). Human Kinetics Publishers Inc. https://doi.org/10.1123/ijsnem.2017-0429 

Gibala, M. J., Little, J. P., Macdonald, M. J., & Hawley, J. A. (2012). Physiological adaptations to low- volume, high-intensity interval training in health and disease. Journal of Physiology, 590(5), 1077– 1084. https://doi.org/10.1113/jphysiol.2011.224725 

Goodman, B. E. (2010). Insights into digestion and absorption of major nutrients in humans. American Journal of Physiology - Advances in Physiology Education, 34(2), 44–53. https://doi.org/10.1152/advan.00094.2009 

Greenleaf, J. E., Jackson, C. G. R., Geelen, G., Keil, L. C., Hinghofer-Szalkay, H., & Whittam, J. H. (1998). Plasma volume expansion with oral fluids in hypohydrated men at rest and during exercise.
 Aviation Space and Environmental Medicine, 69(9), 837–844. https://europepmc.org/article/med/9737753 

Greenleaf, J. E., Looft-Wilson, R., Wisherd, J. L., Jackson, C. G., Fung, P. P., Ertl, A. C., Barnes, P. R., Jensen, C. D., & Whittam, J. H. (1998). Hypervolemia in men from fluid ingestion at rest and during exercise. Aviation, Space, and Environmental Medicine, 69(4), 374–386. http://www.ncbi.nlm.nih.gov/pubmed/9561285 

Greenleaf Robin Looft-Wilson, J. E., & Wisherd M A McKenzie C D Jensen, J. L. (1997). Pre-exercise hypervolemia and cycle ergometer endurance in men. Biology of Sport, 14, 103–114. https://scholarworks.wm.edu/aspubs/1721 

Greenwood-Van Meerveld, B., Johnson, A. C., & Grundy, D. (2017). Gastrointestinal physiology and function. Handbook of Experimental Pharmacology, 239, 1–16. https://doi.org/10.1007/164_2016_118 

Greer, F. R. (2010). Vitamin K the basics-What’s new? Early Human Development, 86(SUPPL. 1), 43–47. https://doi.org/10.1016/j.earlhumdev.2010.01.015 

Greising, S. M., Gransee, H. M., Mantilla, C. B., & Sieck, G. C. (2012). Systems biology of skeletal muscle: Fiber type as an organizing principle. Wiley Interdisciplinary Reviews: Systems Biology and Medicine, 4(5), 457–473. https://doi.org/10.1002/wsbm.1184 

Guest, N. S., VanDusseldorp, T. A., Nelson, M. T., Grgic, J., Schoenfeld, B. J., Jenkins, N. D. M., Arent, S. M., Antonio, J., Stout, J. R., Trexler, E. T., Smith-Ryan, A. E., Goldstein, E. R., Kalman, D. S., & Campbell, B. I. (2021). International Society of Sports Nutrition position stand: caffeine and
 exercise performance. Journal of the International Society of Sports Nutrition, 18(1), 1. https://doi.org/10.1186/s12970-020-00383-4 

Guillochon, M., & Rowlands, D. S. (2017). Solid, gel, and liquid carbohydrate format effects on gut comfort and performance. International Journal of Sport Nutrition and Exercise Metabolism, 27(3), 247–254. https://doi.org/10.1123/ijsnem.2016-0211 

Harada, N., & Inagaki, N. (2012). Role of sodium-glucose transporters in glucose uptake of the intestine and kidney. Journal of Diabetes Investigation, 3(4), 352–353. https://doi.org/10.1111/j.2040- 1124.2012.00227.x 

Helge, J. W. (2000). Adaptation to a fat-rich diet: Effects on endurance performance in humans. Sports Medicine, 30(5), 347–357. https://doi.org/10.2165/00007256-200030050-00003 

Herrera, E., & Barbas, C. (2001). Vitamin E: Action, metabolism and perspectives. Journal of Physiology and Biochemistry, 57(1), 43–56. https://doi.org/10.1007/bf03179812 

Hew-Butler, T., Loi, V., Pani, A., & Rosner, M. H. (2017). Exercise-Associated hyponatremia: 2017 update. Frontiers in Medicine, 4(MAR), 1. https://doi.org/10.3389/fmed.2017.00021 

Hiner, A. (2018). Electrolyte series: magnesium. Nursing Critical Care, 13(1), 15–19. https://doi.org/10.1097/01.CCN.0000527218.03934.56 

Hingst, J. R., Bruhn, L., Hansen, M. B., Rosschou, M. F., Birk, J. B., Fentz, J., Foretz, M., Viollet, B., Sakamoto, K., Færgeman, N. J., Havelund, J. F., Parker, B. L., James, D. E., Kiens, B., Richter, E. A., Jensen, J., & Wojtaszewski, J. F. P. (2018). Exercise-induced molecular mechanisms promoting glycogen supercompensation in human skeletal muscle. Molecular Metabolism, 16, 24–34. https://doi.org/10.1016/j.molmet.2018.07.001 

Holway, F. E., & Spriet, L. L. (2011). Sport-specific nutrition: Practical strategies for team sports. Journal of Sports Sciences, 29(SUPPL. 1). https://doi.org/10.1080/02640414.2011.605459 

Jäger, R., Purpura, M., Shao, A., Inoue, T., & Kreider, R. B. (2011). Analysis of the efficacy, safety, and regulatory status of novel forms of creatine. Amino Acids, 40(5), 1369–1383. https://doi.org/10.1007/s00726-011-0874-6 

Jeukendrup, A. (2013). The new carbohydrate intake recommendations. Nestle Nutrition Institute Workshop Series, 75, 63–71. https://doi.org/10.1159/000345820 

Jeukendrup, A. E. (2008). Carbohydrate feeding during exercise. European Journal of Sport Science, 8(2), 77–86. https://doi.org/10.1080/17461390801918971 

Jeukendrup, A. E. (2010). Carbohydrate and exercise performance: The role of multiple transportable carbohydrates. Current Opinion in Clinical Nutrition and Metabolic Care, 13(4), 452–457. https://doi.org/10.1097/MCO.0b013e328339de9f 

Jeukendrup, & Gleeson. (2018). Sport nutrition (3th ed.). Human Kinetics Publishers Inc. 

Jones, A. M., Thompson, C., Wylie, L. J., & Vanhatalo, A. (2018). Dietary nitrate and physical performance. Annual Review of Nutrition, 38, 303–328. https://doi.org/10.1146/annurev-nutr- 082117-051622 

Kaur, N., Chugh, V., & Gupta, A. K. (2014). Essential fatty acids as functional components of foods- a review. Journal of Food Science and Technology, 51(10), 2289–2303. https://doi.org/10.1007/s13197-012-0677-0 

King, A. J., Rowe, J. T., & Burke, L. M. (2020). Carbohydrate hydrogel products do not improve performance or gastrointestinal distress during moderate-intensity endurance exercise. International Journal of Sport Nutrition and Exercise Metabolism, 30(5), 305–314. https://doi.org/10.1123/IJSNEM.2020-0102 

Knapik, J. J., Steelman, R. A., Hoedebecke, S. S., Austin, K. G., Farina, E. K., & Lieberman, H. R. (2016). Prevalence of Dietary Supplement Use by Athletes: Systematic Review and Meta-Analysis. Sports Med, 46, 103–123. https://doi.org/10.1007/s40279-015-0387-7 

Knuiman, P., Hopman, M. T. E., & Mensink, M. (2015). Glycogen availability and skeletal muscle adaptations with endurance and resistance exercise. In Nutrition and Metabolism (Vol. 12, Issue 1, pp. 1–11). BioMed Central Ltd. https://doi.org/10.1186/s12986-015-0055-9 

Koopman, R., Pannemans, D. L. E., Jeukendrup, A. E., Gijsen, A. P., Senden, J. M. G., Halliday, D., Saris, W. H. M., Van Loon, L. J. C., & Wagenmakers, A. J. M. (2004). Combined ingestion of protein and carbohydrate improves protein balance during ultra-endurance exercise. American Journal of Physiology - Endocrinology and Metabolism, 287(4 50-4), 712–720. https://doi.org/10.1152/ajpendo.00543.2003 

Koskinen, S. O. A., Heinemeier, K. M., Olesen, J. L., Langberg, H., & Kjaer, M. (2004). Physical exercise can influence local levels of matrix metalloproteinases and their inhibitors in tendon-related connective tissue. Journal of Applied Physiology, 96(3), 861–864. https://doi.org/10.1152/japplphysiol.00489.2003 

Kouw, I. W. K., Holwerda, A. M., Trommelen, J., Kramer, I. F., Bastiaanse, J., Halson, S. L., Wodzig, W. K. W. H., Verdijk, L. B., & van Loon, L. J. C. (2017). Protein ingestion before sleep increases overnight muscle protein synthesis rates in healthy older men: A randomized controlled trial. Journal of Nutrition, 147(12), 2252–2261. https://doi.org/10.3945/jn.117.254532 

Lagerwaard, B., Keijer, J., McCully, K. K., de Boer, V. C. J., & Nieuwenhuizen, A. G. (2019). In vivo assessment of muscle mitochondrial function in healthy, young males in relation to parameters of aerobic fitness. European Journal of Applied Physiology, 119(8), 1799–1808. https://doi.org/10.1007/s00421-019-04169-8 

Lancha Junior, A. H., de Salles Painelli, V., Saunders, B., & Artioli, G. G. (2015). Nutritional Strategies to Modulate Intracellular and Extracellular Buffering Capacity During High-Intensity Exercise. Sports Medicine, 45(1), 71–81. https://doi.org/10.1007/s40279-015-0397-5 

Larson-Meyer, D. E., & Willis, K. S. (2010). Vitamin D and Athletes. Current Sports Medicine Reports, 9(4), 220–226. https://doi.org/10.1249/JSR.0b013e3181e7dd45 

Lee Hamm, L., Nakhoul, N., & Hering-Smith, K. S. (2015). Acid-base homeostasis. Clinical Journal of the American Society of Nephrology, 10(12), 2232–2242. https://doi.org/10.2215/CJN.07400715 

Lee, M. J. C., Hammond, K. M., Vasdev, A., Poole, K. L., Impey, S. G., Close, G. L., & Morton, J. P. (2014). Self-selecting fluid intake while maintaining high carbohydrate availability does not impair half- marathon performance. International Journal of Sports Medicine, 35(14), 1216–1222. https://doi.org/10.1055/s-0034-1375635 

Leiper, J. B. (2015). Fate of ingested fluids: Factors affecting gastric emptying and intestinal absorption of beverages in humans. Nutrition Reviews, 73(suppl_2), 57–72. https://doi.org/10.1093/nutrit/nuv032 

Longhurts, R. (2016). Semi-structered interviews and focus groups. In R. Rojek (Ed.), Key methods in geography (3th ed., pp. 143–156). SAGE. 

Lundberg, J. O., Carlström, M., & Weitzberg, E. (2018). Metabolic Effects of Dietary Nitrate in Health and Disease. Cell Metabolism, 28(1), 9–22. https://doi.org/10.1016/j.cmet.2018.06.007 

Maganaris, C. N., & Maughan, R. J. (1998). Creatine supplementation enhances maximum voluntary isometric force and endurance capacity in resistance trained men. Acta Physiologica Scandinavica, 163(3), 279–287. https://doi.org/10.1046/j.1365-201x.1998.00395.x 

Margolis, L. M., & O’Fallon, K. S. (2020). Utility of Ketone Supplementation to Enhance Physical Performance: A Systematic Review. Advances in Nutrition, 11(2), 412–419. https://doi.org/10.1093/advances/nmz104 

Maté-Muñoz, J. L., Lougedo, J. H., Garnacho-Castaño, M. V., Veiga-Herreros, P., Lozano-Estevan, M. D. C., García-Fernández, P., de Jesús, F., Guodemar-Pérez, J., San Juan, A. F., & Domínguez, R. (2018). Effects of .-alanine supplementation during a 5-week strength training program: a randomized, controlled study. Journal of the International Society of Sports Nutrition, 15(1), 19. https://doi.org/10.1186/s12970-018-0224-0 

Maughan, R. J., Burke, L. M., Dvorak, J., Larson-Meyer, D. E., Peeling, P., Phillips, S. M., Rawson, E. S., 

Walsh, N. P., Garthe, I., Geyer, H., Meeusen, R., Van Loon, L., Shirreffs, S. M., Spriet, L. L., Stuart, M., Vernec, A., Currell, K., Ali, V. M., Budgett, R. G. M., ... Engebretsen, L. (2018). IOC consensus statement: Dietary supplements and the high-performance athlete. International Journal of Sport Nutrition and Exercise Metabolism, 28(2), 104–125. https://doi.org/10.1123/ijsnem.2018-0020 

McArdle, W. D., Katch, F. I., & Katch, V. L. (2016). Essential of exercise physiology (8th ed.). Lippincott Williams and Wilkins. 

McMahon, N. F., Leveritt, M. D., & Pavey, T. G. (2017). The Effect of Dietary Nitrate Supplementation on Endurance Exercise Performance in Healthy Adults: A Systematic Review and Meta-Analysis. In Sports Medicine (Vol. 47, Issue 4, pp. 735–756). Springer International Publishing. https://doi.org/10.1007/s40279-016-0617-7 

Mendez-Villanueva, A., Edge, J., Suriano, R., Hamer, P., & Bishop, D. (2012). The Recovery of Repeated- Sprint Exercise Is Associated with PCr Resynthesis, while Muscle pH and EMG Amplitude Remain Depressed. PLoS ONE, 7(12). https://doi.org/10.1371/journal.pone.0051977 

Mujika, I., & Burke, L. M. (2011). Nutrition in team sports. Annals of Nutrition and Metabolism, 57(SUPPL. 2), 26–35. https://doi.org/10.1159/000322700 

Murray, B., & Rosenbloom, C. (2018). Fundamentals of glycogen metabolism for coaches and athletes. Nutrition Reviews, 76(4), 243–259. https://doi.org/10.1093/NUTRIT/NUY001 

Nils-Gerrit Wunsch. (2020, November 25). Global sports nutrition market 2018-2023. Statista. https://www-statista-com.ezproxy.library.wur.nl/statistics/450168/global-sports-nutrition- market/ 

Noakes, T. D., & Speedy, D. B. (2006). Case proven: Exercise associated hyponatraemia is due to overdrinking. So why did it take 20 years before the original evidence was accepted? British Journal of Sports Medicine, 40(7), 567–572. https://doi.org/10.1136/bjsm.2005.020354 

O’Brien, W. J., Stannard, S. R., Clarke, J. A., & Rowlands, D. S. (2013). Fructose-maltodextrin ratio governs exogenous and other cho oxidation and performance. Medicine and Science in Sports and Exercise, 45(9), 1814–1824. https://doi.org/10.1249/MSS.0b013e31828e12d4 

O’Neal, E. K., Wingo, J. E., Richardson, M. T., Leeper, J. D., Neggers, Y. H., & Bishop, P. A. (2011). Half- marathon and full-marathon runners’ hydration practices and perceptions. Journal of Athletic Training, 46(6), 581–591. https://doi.org/10.4085/1062-6050-46.6.581 

Office of Dietary Supplements. (2021, March 26). Phosphorus - Health Professional Fact Sheet. https://ods.od.nih.gov/factsheets/Phosphorus-HealthProfessional/ 

Oliveira, C., Ferreira, D., Caetano, C., Granja, D., Pinto, R., Mendes, B., & Sousa, M. (2017). Nutrition and Supplementation in Soccer. Sports, 5(2), 28. https://doi.org/10.3390/sports5020028 

Orrù, S., Imperlini, E., Nigro, E., Alfieri, A., Cevenini, A., Polito, R., Daniele, A., Buono, P., & Mancini, A. (2018). Role of functional beverages on sport performance and recovery. Nutrients, 10(10), 1470. https://doi.org/10.3390/nu10101470 

Padayatty, S. J., Katz, A., Wang, Y., Eck, P., Kwon, O., Lee, J. H., Chen, S., Corpe, C., Levine, M., Dutta, A., & Dutta, S. K. (2003). Vitamin C as an Antioxidant: Evaluation of Its Role in Disease Prevention.
 Journal of the American College of Nutrition, 22(1), 18–35. https://doi.org/10.1080/07315724.2003.10719272 

Paulsen, G., Hamarsland, H., Cumming, K. T., Johansen, R. E., Hulmi, J. J., Børsheim, E., Wiig, H., Garthe, I., & Raastad, T. (2014). Vitamin C and E supplementation alters protein signalling after a strength training session, but not muscle growth during 10 weeks of training. Journal of Physiology,
 592(24), 5391–5408. https://doi.org/10.1113/jphysiol.2014.279950 

Paulsen, Gøran, Cumming, K. T., Holden, G., Hallén, J., Rønnestad, B. R., Sveen, O., Skaug, A., Paur, I., Bastani, N. E., Østgaard, H. N., Buer, C., Midttun, M., Freuchen, F., Wiig, H., Ulseth, E. T., Garthe, I., Blomhoff, R., Benestad, H. B., & Raastad, T. (2014). Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: A double-blind, randomised, controlled trial. Journal of Physiology, 592(8), 1887–1901. https://doi.org/10.1113/jphysiol.2013.267419 

Pawlak-Chaouch, M., Boissière, J., Gamelin, F. X., Cuvelier, G., Berthoin, S., & Aucouturier, J. (2016). Effect of dietary nitrate supplementation on metabolic rate during rest and exercise in human: A systematic review and a meta-analysis. Nitric Oxide - Biology and Chemistry, 53, 65–76. https://doi.org/10.1016/j.niox.2016.01.001 

Perez-Idarraga, A., & Aragon-Vargas, L. F. (2014). Postexercise rehydration: Potassium-rich drinks versus water and a sports drink. Applied Physiology, Nutrition and Metabolism, 39(10), 1167– 1174. https://doi.org/10.1139/apnm-2013-0434 

Perim, P., Marticorena, F. M., Ribeiro, F., Barreto, G., Gobbi, N., Kerksick, C., Dolan, E., & Saunders, B. (2019). Can the Skeletal Muscle Carnosine Response to Beta-Alanine Supplementation Be Optimized? Frontiers in Nutrition, 6, 135. https://doi.org/10.3389/fnut.2019.00135 

Peternelj, T. T., & Coombes, J. S. (2011). Antioxidant supplementation during exercise training: Beneficial or detrimental? Sports Medicine, 41(12), 1043–1069. https://doi.org/10.2165/11594400-000000000-00000 

Pfeiffer, B., Stellingwerff, T., Zaltas, E., & Jeukendrup, A. E. (2010). CHO oxidation from a CHO Gel compared with a drink during exercise. Medicine and Science in Sports and Exercise, 42(11), 2038– 2045. https://doi.org/10.1249/MSS.0b013e3181e0efe6 

Pfortmueller, C. A., Uehlinger, D., von Haehling, S., & Schefold, J. C. (2018). Serum chloride levels in critical illness—the hidden story. Intensive Care Medicine Experimental, 6(1), 10. https://doi.org/10.1186/s40635-018-0174-5 

Philpott, J. D., Witard, O. C., & Galloway, S. D. R. (2018). Applications of omega-3 polyunsaturated fatty acid supplementation for sport performance. Research in Sports Medicine, 27(2), 219–237. https://doi.org/10.1080/15438627.2018.1550401 

Pinckaers, P. J. M., Churchward-Venne, T. A., Bailey, D., & van Loon, L. J. C. (2017). Ketone Bodies and Exercise Performance: The Next Magic Bullet or Merely Hype? Sports Medicine, 47(3), 383–391. https://doi.org/10.1007/s40279-016-0577-y 

Potgieter, S. (2013). Sport nutrition: A review of the latest guidelines for exercise and sport nutrition from the American College of Sport Nutrition, the International Olympic Committee and the International Society for Sports Nutrition. South African Journal of Clinical Nutrition, 26(1), 6–16. https://doi.org/10.1080/16070658.2013.11734434 

Powers, M. E., Arnold, B. L., Weltman, A. L., Perrin, D. H., Mistry, D., Kahler, D. M., Kraemer, W., & Volek, J. (2003). Creatine supplementation increases total body water without altering fluid distribution. Journal of Athletic Training, 38(1), 44–50. /pmc/articles/PMC155510/ 

Prompers, J. J., Wessels, B., Kemp, G. J., & Nicolay, K. (2014). Mitochondria: Investigation of in vivo muscle mitochondrial function by 31P magnetic resonance spectroscopy. International Journal of Biochemistry and Cell Biology, 50(1), 67–72. https://doi.org/10.1016/j.biocel.2014.02.014 

Rehrer, N., & Van Vliet, L. (2007). Sodium Loading Aids Fluid Balance and Reduces Physiological Strain of Trained Men Exercising in the Heat Related papers. Medicine & Science in Sports & Exercise, 39(1), 123–130. https://doi.org/10.1249/01.mss.0000241639.97972.4a 

Rodriguez, N., Di Marco, N., & Langley, S. (2009). American College of Sports Medicine position stand. Nutrition and athletic performance. Medicine and Science in Sports and Exercise, 41(3), 709–731. https://doi.org/10.1249/MSS.0b013e31890eb86 

Rollo, I., & Williams, C. (2011). Effect of mouth-rinsing carbohydrate solutions on endurance performance. Sports Medicine, 41(6), 449–461. https://doi.org/10.2165/11588730-000000000- 00000 

Rosenbloom, C. (2012). Food and fluid guidelines before, during, and after exercise. Nutrition Today, 47(2), 63–69. https://doi.org/10.1097/NT.0b013e31824c5cb8 

Rowlands, D. S., Swift, M., Ros, M., & Green, J. G. (2012). Composite versus single transportable carbohydrate solution enhances race and laboratory cycling performance. Applied Physiology, Nutrition and Metabolism, 37(3), 425–436. https://doi.org/10.1139/H2012-013 

Santamaria, P. (2006). Nitrate in vegetables: Toxicity, content, intake and EC regulation. Journal of the Science of Food and Agriculture, 86(1), 10–17. https://doi.org/10.1002/jsfa.2351 

Sareban, M., Zügel, D., Koehler, K., Hartveg, P., Zügel, M., Schumann, U., Steinacker, J. M., & Treff, G. (2016). Carbohydrate intake in form of gel is associated with increased gastrointestinal distress but not with performance differences compared with liquid carbohydrate ingestion during simulated long-distance triathlon. International Journal of Sport Nutrition and Exercise Metabolism, 26(2), 114–122. https://doi.org/10.1123/ijsnem.2015-0060 

Saunders, B., Elliott-Sale, K., Artioli, G. G., Swinton, P. A., Dolan, E., Roschel, H., Sale, C., & Gualano, B. (2017). .-Alanine supplementation to improve exercise capacity and performance: A systematic review and meta-Analysis. British Journal of Sports Medicine, 51(8), 658–669. https://doi.org/10.1136/bjsports-2016-096396 

Sebastiaan Horn. (2018, May 16). De isotone sportdrank! Duursport. https://www.duursport.nl/blog/sportdrank-isotoon/ 

Seifter, J. L. (2019). Body Fluid Compartments, Cell Membrane Ion Transport, Electrolyte Concentrations, and Acid-Base Balance. In Seminars in Nephrology (Vol. 39, Issue 4, pp. 368–379). W.B. Saunders. https://doi.org/10.1016/j.semnephrol.2019.04.006 

Shirreffs, S. M. (2009). Hydration in sport and exercise: Water, sports drinks and other drinks. Nutrition Bulletin, 34(4), 374–379. https://doi.org/10.1111/j.1467-3010.2009.01790.x 

Shirreffs, Susan M. (2003). The optimal sports drink. Schweizerische Zeitschrift Fur Sportmedizin Und Sporttraumatologie, 51(1), 25–30. 

Sims, S. T., Rehrer, N. J., Bell, M. L., & Cotter, J. D. (2007). Preexercise sodium loading aids fluid balance and endurance for women exercising in the heat. Journal of Applied Physiology, 103(2), 534–541. https://doi.org/10.1152/japplphysiol.01203.2006 

Spriet, L. L. (2014a). New insights into the interaction of carbohydrate and fat metabolism during exercise. Sports Medicine, 44(SUPPL.1), 87–96. https://doi.org/10.1007/s40279-014-0154-1 

Spriet, L. L. (2014b). Exercise and Sport Performance with Low Doses of Caffeine. Sports Medicine, 44(2), 175–184. https://doi.org/10.1007/s40279-014-0257-8 

Stafford, D. W. (2005). The vitamin K cycle. Journal of Thrombosis and Haemostasis, 3(8), 1873–1878. https://doi.org/10.1111/j.1538-7836.2005.01419.x 

Steenge, G. R., Simpson, E. J., & Greenhaff, P. L. (2000). Protein- and carbohydrate-induced augmentation of whole body creatine retention in humans. Journal of Applied Physiology, 89(3), 1165–1171. https://doi.org/10.1152/jappl.2000.89.3.1165 

Stegen, S., Blancquaert, L., Everaert, I., Bex, T., Taes, Y., Calders, P., Achten, E., & Derave, W. (2013). Meal and beta-alanine coingestion enhances muscle carnosine loading. Medicine and Science in Sports and Exercise, 45(8), 1478–1485. https://doi.org/10.1249/MSS.0b013e31828ab073 

Strazzullo, P., & Leclercq, C. (2014). Sodium. Advances in Nutrition, 5(2), 188–190. https://doi.org/10.3945/an.113.005215 

Strobel, N. A., Peake, J. M., Matsumoto, A., Marsh, S. A., Coombes, J. S., Wadley, G. D., Strobel, N. A., Peake, J. M., Matsumoto, A., Marsh, S. A., Coombes, J. 
S., & Antioxidant, G. D. W. (2011). Supple- mentation Reduces Skeletal Muscle Mitochondrial Biogenesis. Med. Sci. Sports Exerc, 43(6), 1017– 1024. https://doi.org/10.1249/MSS.0b013e318203afa3 

Suhett, L. G., de Miranda Monteiro Santos, R., Silveira, B. K. S., Leal, A. C. G., de Brito, A. D. M., de Novaes, J. F., & Lucia, C. M. Della. (2021). Effects of curcumin supplementation on sport and physical exercise: a systematic review. Critical Reviews in Food Science and Nutrition, 61(6), 946– 958. https://doi.org/10.1080/10408398.2020.1749025 

Tang, J. E., Moore, D. R., Kujbida, G. W., Tarnopolsky, M. A., & Phillips, S. M. (2009). Ingestion of whey hydrolysate, casein, or soy protein isolate: Effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. Journal of Applied Physiology, 107(3), 987–992. https://doi.org/10.1152/japplphysiol.00076.2009 

Thielecke, F., & Blannin, A. (2020). Omega-3 fatty acids for sport performance—are they equally beneficial for athletes and amateurs? A narrative review. Nutrients, 12(12), 1–28. https://doi.org/10.3390/nu12123712 

Thompson, C., Wylie, L. J., Fulford, J., Kelly, J., Black, M. I., McDonagh, S. T. J., Jeukendrup, A. E., Vanhatalo, A., & Jones, A. M. (2015). Dietary nitrate improves sprint performance and cognitive function during prolonged intermittent exercise. European Journal of Applied Physiology, 115(9), 1825–1834. https://doi.org/10.1007/s00421-015-3166-0 

Tipton, K. D., Rasmussen, B. B., Miller, S. L., Wolf, S. E., Owens-Stovall, S. K., Petrini, B. E., & Wolfe, R. R. (2001). Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to
 resistance exercise. American Journal of Physiology - Endocrinology and Metabolism, 281(2 44-2). https://doi.org/10.1152/ajpendo.2001.281.2.e197 

Triplett, D., Doyle, J. A., Rupp, J. C., & Benardot, D. (2010). An isocaloric glucose-fructose beverage’s effect on simulated 100-km cycling performance compared with a glucose-only beverage. International Journal of Sport Nutrition and Exercise Metabolism, 20(2), 122–131. https://doi.org/10.1123/ijsnem.20.2.122 

Urdampilleta, A., Arribalzaga, S., Viribay, A., Castañeda-Babarro, A., Seco-Calvo, J., & Mielgo-Ayuso, J. (2020). Effects of 120 vs. 60 and 90 g/h carbohydrate intake during a trail marathon on neuromuscular function and high intensity run capacity recovery. Nutrients, 12(7), 1–17. https://doi.org/10.3390/nu12072094 

US Department of Health and Human services and US Department of Agriculture. (2015). 2015-2020 Dietary Guidelines for Americans. http://health.gov/dietaryguidelines/2015/guidelines/. 

Van Loon, L. J. C., Greenhaff, P. L., Constantin-Teodosiu, D., Saris, W. H. M., & Wagenmakers, A. J. M. (2001). The effects of increasing exercise intensity on muscle fuel utilisation in humans. Journal of Physiology, 536(1), 295–304. https://doi.org/10.1111/j.1469-7793.2001.00295.x 

Van Nieuwenhoven, M. A., Brummer, R. J. M., & Brouns, F. (2000). Gastrointestinal function during exercise: Comparison of water, sports drink, and sports drink with caffeine. Journal of Applied Physiology, 89(3), 1079–1085. https://doi.org/10.1152/jappl.2000.89.3.1079 

Van Rosendal, S. P., Osborne, M. A., Fassett, R. G., & Coombes, J. S. (2010). Guidelines for glycerol use in hyperhydration and rehydration associated with exercise. Sports Medicine, 40(2), 113–139. https://doi.org/10.2165/11530760-000000000-00000 

Vist, G. E., & Maughan, R. J. (1995). The effect of osmolality and carbohydrate content on the rate of gastric emptying of liquids in man. The Journal of Physiology, 486(2), 523–531. https://doi.org/10.1113/jphysiol.1995.sp020831 

Voedingscentrum Nederland. (2016). Sport en voeding (5th ed.). Stichting Voedingscentrum Nederland. https://webshop.voedingscentrum.nl/producten/gezond-eten/alles-over-sport-en-voeding/ 

Volek, J. S., Freidenreich, D. J., Saenz, C., Kunces, L. J., Creighton, B. C., Bartley, J. M., Davitt, P. M., Munoz, C. X., Anderson, J. M., Maresh, C. M., Lee, E. C., Schuenke, M. D., Aerni, G., Kraemer, W. J., & Phinney, S. D. (2016). Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism: Clinical and Experimental, 65(3), 100–110. https://doi.org/10.1016/j.metabol.2015.10.028 

Volek, J. S., & Rawson, E. S. (2004). Scientific basis and practical aspects of creatine supplementation for athletes. In Nutrition (Vol. 20, Issues 7–8, pp. 609–614). Elsevier. https://doi.org/10.1016/j.nut.2004.04.014 

Wallis, G. A., Rowlands, D. S., Shaw, C., Jentjens, R. L. P. G., & Jeukendrup, A. E. (2005). Oxidation of combined ingestion of maltodextrins and fructose during exercise. Medicine and Science in Sports and Exercise, 37(3), 426–432. https://doi.org/10.1249/01.MSS.0000155399.23358.82 

Wardenaar, F., Brinkmans, N., Ceelen, I., Van Rooij, B., Mensink, M., Witkamp, R., & De Vries, J. (2017). Micronutrient intakes in 553 dutch elite and sub-elite athletes: Prevalence of low and high intakes
 in users and non-users of nutritional supplements. Nutrients, 9(2), 142. https://doi.org/10.3390/nu9020142 

White, B. (2009). American Family Physician. In American Family Physician (Vol. 80, Issue 4). www.aafp.org/afp. 

Williams, C., & Rollo, I. (2015). Carbohydrate Nutrition and Team Sport Performance. Sports Medicine, 45(1), 13–22. https://doi.org/10.1007/s40279-015-0399-3 

Wylie, L. J., Bailey, S. J., Kelly, J., Blackwell, J. R., Vanhatalo, A., & Jones, A. M. (2016). Influence of beetroot juice supplementation on intermittent exercise performance. European Journal of Applied Physiology, 116, 415–425. https://doi.org/10.1007/s00421-015-3296-4 

Yeo, S. E., Jentjens, R. L. P. G., Wallis, G. A., & Jeukendrup, A. E. (2005). Caffeine increases exogenous carbohydrate oxidation during exercise. Journal of Applied Physiology, 99(3), 844–850. https://doi.org/10.1152/japplphysiol.00170.2005 

Zhang, X., O’Kennedy, X., & Morton, J. P. (2015). Extreme variation of nutritional composition and osmolality of commercially available carbohydrate energy gels. International Journal of Sport Nutrition and Exercise Metabolism, 25(5), 504–509. https://doi.org/10.1123/ijsnem.2014-0215