The Ultimate Guide to Boosting Performance for Hyrox, Marathons and Endurance Sports

Introduction

When it comes to fuelling the human body for endurance sports like half marathons, full marathons, Hyrox and triathlon, carbohydrates reign supreme. But what exactly are carbohydrates, and why are they so essential for athletes aiming to push their limits? Carbohydrates are a large group of organic compounds found in foods and living tissues, playing a crucial role in providing the energy needed for our bodies to perform optimally. Though the topic of carbohydrates is vast, with a wealth of research and evidence, our goal today is to distil this complex subject into a practical guide for athletes and endurance enthusiasts alike.

What is a Carbohydrate?

At its core, a carbohydrate is a chemical structure made up of sugar molecules, classified by their degree of polymerisation, which is essentially the number and type of molecules that come together to form a carbohydrate. This classification ranges from simple sugars, like glucose, to complex forms such as starches and fibres. The body’s ability to break down these structures to produce ATP, our primary energy currency, is key to understanding how carbohydrates fuel endurance performance.

In this article, we will delve into how carbohydrates support athletic performance, especially in the context of endurance sports. We’ll explore how the body utilises carbohydrates during exercise, strategies for optimising carbohydrate intake before and during a race, and the science behind avoiding the dreaded "wall" that many of us have likely encountered in our feats of endurance. Whether you're a seasoned marathoner, gearing up for your first Hyrox, or looking to get into Triathlon, this discussion will equip you with the knowledge to harness the power of carbohydrates and push your performance to new heights.

Understanding Carbohydrates

Carbohydrates should be the cornerstone of an endurance athlete's diet, providing the essential fuel required for sustained performance. As a primary energy source, carbs are broken down into glucose, which is stored in the muscles and liver as glycogen. During an event of endurance, your body relies heavily on these glycogen stores to maintain energy levels and keep you moving forward. Carbohydrates from our glycogen stores or blood sugar are broken down and digested to yield an energy-rich compound called ATP, which is produced through the oxidation of glucose molecules (electrons stripped from glucose molecules). (Jeukendrup and Jentjens, 2000). Each gram of carbohydrate provides 4 calories of energy, which can prove helpful when aiming to provide the body with the fuel it needs for continued performance.

Not all carbohydrates are created equal, and understanding the difference between simple and complex carbs is crucial for maximising the efficiency of your training and race-day nutrition. Simple carbs (short chains of sugar molecules) provide a quick energy boost but can lead to rapid spikes and crashes in blood sugar levels. In contrast, complex carbs (longer chains of sugar molecules), found in foods like whole grains, legumes, fruits, and vegetables, are digested more slowly, offering a steady release of energy to power you through longer runs.

Sugars (monosaccharides) is a far more recognised term associated with carbohydrates and is effectively just a type of carbohydrate with 1 or 2 degrees of polymerisation. Other examples included oligosaccharides (short-chain carbohydrates) (DP 3-9), or polysaccharides (DP ≥10). It is also important to note that, while this structure and primary chemistry are the main driving force behind physiological effects on the body, the physical property can have an influence too. For example, consuming carbohydrates in a complex food structure, the level of water solubility, the hydration of the consumer, the consumption in gel formation or in combination with other macronutrients, or when consumed within cell walls. These factors are also important to consider and will be considered throughout the guidelines presented in this article.

The most important thing to consider is how we can balance our carbohydrate intake with the demands of our training plan to ensure that glycogen stores are adequately topped up. This facilitates optimal performance. By strategically consuming the right types of carbs, we can enhance our endurance, delay fatigue, and ultimately cross the finish line with confidence.

Carbohydrates and Endurance Performance

The Importance of a High-Carb Diet

With a rounded appreciation for the humble carbohydrate and a knowledge of their importance, it is now possible to delve into their crucial role in endurance performance. I’d like to think that the indispensable contribution of carbohydrates to endurance performance has been established. The energy demands of activities like marathons, triathlons and Hyrox competitions are intense and immense. They require athletes to strategically manage their carbohydrate intake to sustain energy levels, maximise performance and mitigate burnout.

As previously alluded to, during prolonged endurance exercise, your body relies heavily on stored glycogen as its primary fuel source. Glycogen, stored in both your muscles and liver, is broken down into glucose to be used for energy. The availability of these glycogen stores directly impacts your ability to maintain pace and intensity throughout your event. When glycogen levels are sufficient, your muscles have a steady supply of energy, allowing you to maintain peak performance. However, as these stores become depleted, your energy levels dwindle, leading to fatigue, decreased performance, and the dreaded "bonk" or "hitting the wall."

It has long been acknowledged that a high-carb diet increases both glycogen stores and exercise performance (Bergstrom et al., 1967). Studies dating back to the 1960s and 70s have shown that a low-carb diet (60-100g/day) will deplete muscle glycogen stores far quicker than a higher carbohydrate diet (400-700g/day) (Costill et al., 1971). This occurred over 3 days, with three 16.1km runs – a distance not too far off our half marathon or Hyrox times.

These distances are prolonged and performed at a high intensity, especially when we are aiming to smash personal bests and beat the competition. This results in a vigorous intensity that requires carbohydrates as the primary fuel source (Holloszy and Kohrt, 1996). The intensity and Duration (and body mass of the individual) will dictate individual requirements for consumption but there are clear links between exercise and a decreased rate of carbohydrate oxidation (utilisation) (Coyle, 1992). So much so, that the stage at which an athlete fatigues is the point where glycogen and glucose provision decreases too (Bergstrom and Hultman, 1992).

The Carb-Loading Process

To optimise endurance performance, it’s crucial to not only consume adequate carbohydrates before your run but also to strategically refuel during the event. This approach helps to delay glycogen depletion and maintain a steady supply of energy throughout your race. Pre-race carbohydrate loading is a well-established strategy among endurance athletes. By increasing your carbohydrate intake in the days leading up to a race, you can top off glycogen stores, ensuring that your muscles are fully stocked and ready to perform at their best. This process involves consuming more complex carbohydrates, like whole grains, pasta, and starchy vegetables, which provide a sustained release of energy and keep your glycogen stores nice and high.

The process of gradually increasing carbohydrate intake in the days before a race or an event is a proven strategy. Carbohydrate-rich meals and snacks (e.g., pasta, rice, couscous, rice cakes, bread, fruits, etc.) Depending on the length of the event a carb-load may start up to 1 week out. The science-backed recommendation is to consume between 8g/kg body mass and 10g/kg body mass per day in the build-up. As long as the amount ingested is adequate, the type (e.g., source) and form (e.g., state) have no influence on the ergogenic effect of carbohydrates.

Another nuanced alternative is to consume a more aggressive 10-12g/kg body weight of carbs to top off glycogen stores just 24-48 hours prior to competition (Jeukendrup, 2014; Hackney, 2015; Burke, 2007). This option also allows for enhanced hydration as each gram of glycogen holds onto 3 extra millilitres of water (Beck et al., 2015). Either way, the evidence indicates that a high carbohydrate diet can indeed improve performance by 2 to 3% and postpone fatigue by ~20% (Hawley et al., 1997). An important consideration to caveat the preceding points with is the need to action a bit of caution when it comes to the introduction of new foods in the build-up to a race. We should aim to train the gut with the foods we intend to use in the week before the race and the race day itself.

The Story of Chrissie Wellington

Chrissie Wellington’s Ironman World Championship victory in 2007 provides some compelling evidence to support the need and benefit of carb-loading (Wellington, 2012). On the day prior to exercise, Wellington consumed 585g of CHO and 3672 kcal. This may seem excessive for a 60.5kg athlete but research has found that the ingestion of CHO is limited by absorption in the small (glycaemic CHOs) and large intestines (non-glycaemic, fibrous CHOs – thick plant cell wall) and not body weight (Englyst and Englyst, 2005). Carbohydrate consumption is, therefore, often expressed in terms of consumption in grams per unit of time.

Race Day Nutrition

A great framework to consider when race day rolls around is the 180-90-30 principle. This involves consuming carbohydrates and fuelling up for a performance at 3 hours out from the competition (a larger serving of complex carbs), 90 minutes out from the competition (a simple carb source) and 30 minutes out (more simple carbs). Aim for 1-4 grams of carbs per kilogram of body weight in this window to ensure a sufficient supply and delivery of glucose to the working muscles when we cross the start line. What it doesn’t reveal is exactly how much carbohydrate we need. As already mentioned, the exact figure will depend on factors such as body weight and race duration. Nevertheless, there are simple principles that can be followed, offering a target for carbohydrate quantity.

The Intra-Race Strategy

The intra-race fuelling strategy is influenced by a number of factors including duration, intensity and individual considerations (weight and metabolism). However, the following numbers offer a guide that can be utilised to enhance performance:

1-2 Hours of Intense Exercise = 30g/h

2-3 Hours of Intense Exercise = 60g/h

>2.5 Hours of Intense Exercise = 90g/h

There are some important considerations to factor in around these guidelines, especially when we get to the upper end of consumption (i.e., 90g/h). Glucose, alone, can only be ingested and absorbed in the intestine at a rate of 60g/h before it begins to accumulate in the intestine and cause distress (I’m sure we’ve all been there). To reach that desirable +90g/h we can combine sources of carbohydrates. Deriving carbohydrates from fructose (a type of sugar) and glucose or maltodextrin (an oligosaccharide containing 10-20 glucose molecules – fast digesting – small intestine) can override this mechanism, provide the fuel needed for longer distance endurance, and prevent any GI disruption. This is made possible because fructose (from fruits) is a lot slower to digest than the other sugar types (because of the thick plant cell wall) as it needs conversion in the liver (to glucose) before absorption (Douard and Ferraris, 2008). This means that it uses a different protein transporter (GLUT5 as opposed to SGLT1 of glucose) to enter the working muscles because of its unique structure and composition. This combined effect enhances the carbohydrate oxidation rate and thus improves performance. A recent example of this strategy working comes from Ross Edgley who recently admitted to consuming in excess of 120g of carbs per hour during his Yukon River Swim. 1

Energy gels, sports drinks, and easily digestible snacks are popular choices among endurance athletes. These provide a quick infusion of glucose, which can be rapidly absorbed into the bloodstream and delivered to your muscles, helping to maintain energy levels and prolong endurance. Post-race, the focus shifts to recovery, where replenishing glycogen stores is just as important. Consuming carbohydrates within the first 30 minutes after finishing your run is critical for rapid glycogen synthesis. Pairing carbs with a source of protein can further enhance recovery by aiding in muscle repair and reducing soreness.

Understanding the relationship between carbohydrates and endurance performance allows you to tailor your nutrition plan to meet the specific demands of your training and racing schedule. By leveraging the above information you can dial in your carbohydrate intake before during and after your events to enhance performance, delay fatigue, and ultimately, achieve your endurance goals.

The Carbohydrate and Hydration Interaction

For every gram of glycogen stored, the body also stores about 3 grams of water. This water is beneficial because it contributes to overall hydration and helps maintain fluid balance during exercise. This is also the reason that sports drinks and gels are such popular choices for athletes as they provide a combined effect to boost output. The fusion of carbs, water and electrolytes (e.g., sodium, magnesium and potassium) helps to prolong activity. The interaction of carbs and fluids goes beyond this more superficial fact too.

Carbohydrate solutions can enhance fluid absorption in the small intestine. The presence of glucose stimulates sodium absorption, which, in turn, pulls water into the bloodstream. This process helps in maintaining hydration during exercise. Consuming carbohydrate-rich fluids or gels during exercise not only provides energy but also helps in maintaining hydration by ensuring that fluids are absorbed efficiently.

The Potential Dangers and Considerations

Perhaps, the most obvious of all the potential risks associated with carbohydrate consumption during exercise is the gastrointestinal distress it can cause when pushed too far. Consuming too many carbohydrates, especially complex or fibrous ones, close to an event can lead to bloating, cramps, and diarrhoea. This emphasises the need to train your gut as part of your training plan, eating the foods and products you expect to consume on race day. You want to avoid any nasty surprises!

Post-race an individual may experience a hypoglycaemic episode where blood sugar crashes following an Over-reliance on simple carbohydrates. This may manifest in extreme fatigue, dizziness and impaired performance. To mitigate this coming to fruition, it’s important to replenish carbohydrates as soon as possible following the end of the race!

Training for Efficiency

Within the core fundamentals already discussed in this article, there are some nuanced strategies and techniques that can help improve the overall efficiency of carbohydrate utilisation for performance. It is possible to train and teach the body how to optimise its usage of carbohydrates for enhancements on race day. An understanding of the physiological mechanisms that underpin these strategies can help us tailor our fuelling strategy in training to maximise energy output for competition. The following will explore the potential techniques, available for adoption.

1. Training Low, Competing High

A concept popularised around the mid-2000s, this method posits a training schedule that involves training with a low availability of carbohydrates and competing with a far higher availability. This challenges the body to adapt to the relative absence of energy availability and creates a super-compensation mechanism once carbohydrates are loaded for performance. Physiologically, the low availability of glycogen and glucose forces the body to become more reliant on fat as a fuel source. With extended periods of training this way, the body improves its ability to utilise these fat stores as it becomes more efficient at oxidising them during exercise. This can be especially important at the later stages of endurance events, as glycogen stores may be better reserved for when things get tough. The low-carbohydrate training environment can also stimulate mitochondrial biogenesis which stimulates the production of mitochondria in muscle cells and thus enhanced energy production. At the same time, an increase of fat-metabolising enzymes makes the body more efficient at converting fat into usable energy.

This technique may be worth applying to your next training block. Practice training fasted or train on consecutive days without replenishing glycogen stores with carbohydrate-rich food sources. When race day rolls around, top up those glycogen stores again and create that super-compensation for improved performance.

2. Train Hard, Spare Glycogen

The very act of training itself can train the body to conserve glycogen stores and thus improve its overall efficiency during prolonged bouts of exercise. The muscles become capable of performing the same work with less energy expenditure, which helps to preserve glycogen for those latter stages of a race. An effective endurance training plan will also promote enzymatic adaptations that optimise gluconeogenesis (glucose production from non-carbohydrate sources) and glycogenolysis (glycogen breakdown for energy) for a more sustained deposit of energy. Simultaneously, insulin sensitivity may be improved, enabling a more efficient uptake of glucose from the bloodstream that circumvents a reliance on glycogen stores.

An effective training plan that facilitates the outcomes mentioned will vary from sport to sport and race to race. However, a general rule to follow is to incorporate a combination of longer, steady state (zone 2) sessions with shorter bursts of activity like a high-intensity interval training session (zone 4-5). In unison, these approaches will trigger the adaptive responses to optimise energy for endurance.

3. Periodisation

The periodisation of carbohydrate intake involves the adjustment of carb consumption with training volume and intensity. This allows an athlete to align energy availability with training demands and can prove physiologically beneficial. Hormones, such as cortisol and insulin, may become better regulated and thus boost energy levels and recovery. This strategy encompasses a similar super-compensation mechanism to ‘train low, compete high’ too. The muscles are capable of storing a larger-than-normal reservoir of glycogen after a period of depletion. This can prove to be super beneficial come race day.

Consider fuelling with carbs around intense sessions, in the lead-up to a race and on race day itself. Conversely, lighter phases of training (e.g., off-season or the start of a block) may coincide with lower carbohydrate intake to promote that metabolic flexibility and fat adaptation.

The preceding strategies demonstrate the many ways in which carbohydrates can be leveraged to improve our efficiency as athletes. The incorporation of one of these strategies into a training regimen may provide incremental margins capable of enhancing performance by delaying fatigue and increasing sustained energy output.

The Round-Up

The intention of this article was to provide you with a toolbox of ideas for fuelling your performance with carbohydrates. For any endurance athlete, it is incredibly important to dial in an efficient nutrition strategy to enhance outcomes on race day. The meticulous management of carbohydrate consumption before, during and after training and competition can be the difference between success and failure. It can prove to be that significant. So, I encourage you to take heed of the many nuances associated with carbohydrate consumption and apply the fundamentals. If you want to unlock your full athletic potential, carbohydrates are essential. Whether you compete in Hyrox, Marathons, Triathlons or even prolonged team sports (e.g., football), an appreciation for the importance of carbs will always serve you well.

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If you’d like to read about my research in a little more detail, I have provided a long list of references and the papers that I read to inform my knowledge-base.

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