We, at High5 Sports Nutrition and Tri Training Harder, understand the importance of getting your nutrition right so that you can maximise your endurance performance and stay fit and healthy before, during and after your session(s). To that end, we have spoken with numerous athletes and coaches to find out some of the most common problems/issues regarding sports nutrition.
We have tried to answer these questions in as generic and simple terms as possible so that you, the athlete, are best equipped to fuel yourself correctly, whatever your event or discipline. We have also provided a fuller explanation should you want more information on the topic. The science around sports is the same for every human being; we all burn energy, and that energy needs to be replenished. The confusion begins when we try to apply a ‘solve all’ answer to our individual nutrition needs.
We have tried to answer the questions below without referencing specific brands and/or products, so that you can make an informed decision as to your nutritional requirements.
Q: UNDERSTANDING ABSORPTION RATES
A: After swallowing your traditional sports drink (that breaks down into glucose, and not fructose); it reaches the stomach before moving down to your intestine. During that journey, the various types of carbohydrate found in the drink are broken down to glucose by your digestive system. Glucose is the main source of energy for the body during exercise. This Glucose must then pass through the intestine wall, by way of Glucose Transporters and into the blood stream to be taken to the working muscles.
However, the Glucose Transporters only allow Glucose to pass through relatively slowly and this results in a bottleneck at the wall of the intestine. It’s thought that this Glucose ‘bottleneck’ is what limits the maximum amount of carbohydrate your body can absorb, from a traditional sports drink, to around 60 gram per hour. Read more
Maltodextrin: This is a carbohydrate used in many traditional sports drinks. It’s a common type of carbohydrate that’s broken down to glucose by digestion and passes through the wall of the intestine at a maximum rate of 60gram per hour.
Fructose (fruit sugar): Is a unique carbohydrate that’s not broken down to Glucose by digestion. Fructose passes through the wall of the intestine using a completely different set of Transporters to Glucose (GLUT5). Fructose does not get caught in the Glucose ‘bottleneck’ and it can provide your working muscles with an additional 30gram per hour of carbohydrate. (1)(2)(3)(4)(5)(6)
A ratio of 2 parts maltodextrin to 1 part fructose has been shown to be the most effective in providing your muscles with carbohydrate. If we consume 60g glucose per hour, then we can provide our working muscles an additional 30g of carbohydrate per hour through fructose. As you can see from the diagram, 90 gram per hour could be absorbed each hour using a 2:1 fructose formulation.
As carbohydrate is the primary fuel for endurance sport, the more carbohydrate you have available, the faster and further you will be able to go. A number of independent research studies, are based on 2:1 fructose drinks, and they have clearly demonstrated a substantial performance and endurance advantage when compared to traditional sports drink formulations.(5)
When considering absorption rates, the aim is to balance liver release and muscle absorption at 1g/min (7). Despite fuel being used from both the liver and the muscles, hypoglycemia is one of the first reasons athletes fatigue during exercise which takes place when the liver glycogen (fuel) stores are used up. Without carbohydrate ingestion (no sports drinks or food) to suppress liver glucose production, even when only racing or training at between 70-85% VO2Max, these liver glycogen stores will be depleted after around 2 hours (8).
After swallowing food be it in liquid or solid form, the ability for your body to use the ‘food’ is determined by the following four areas:
1) Gastric emptying
2) Intestinal absorption
3) Muscle glucose uptake
4) Oxidation limit carbohydrate use by muscles.
In most studies the stomach has still been fully emptied with doses of carbohydrate between 70-100g/hr (9)(10)(11)(12).
As described above, the intestinal absorption is balanced at approximately 60g/hr of glucose and a further amount of fructose polymers. This is set to 30g/hr as even a limited amount of fructose (50g/hour) (13) produces gastrointestinal discomfort (14). This is because there is limited capacity to absorb fructose in the intestine so it then travels to the colon where metabolism by bacteria produces chemicals that can induce colonic discomfort.
Ingested carbohydrate during exercise is burned by the muscles in place of blood glucose derived from the liver, (15) and this rate of use increases up to an intensity of 60%VO2Max (16)(17). Carbohydrate ingestion during exercise does not however increase the rate of glucose output by the liver during exercise (18)(19)(20). It simply substitutes all or part of the glucose that would be released by the liver and any excess is stored as liver glycogen stores. Trained athletes may oxidise more ingested carbohydrate than untrained athletes (21), but only glucose infused straight into the blood stream (i.e injected) allows muscular oxidation rates />to be increased further (up to 150g/hour).
Q: IS SPORTS NUTRITION FOR ME? – MOST STUDIES SEEM TO BE FOR ATHLETES, NOT NORMAL EVERY DAY PEOPLE LIKE ME.
A: Sports nutrition is applicable to athletes at all levels, in some form. It will differ greatly from individual to individual and there is no set rule that will apply to everyone for how and when to take on nutrition. Humans, however, are all built in the same way; all will burn energy, and all will need to replenish depleted energy stores. Professional athletes are no different to this; they are just extremely fine-tuned examples. At the same time the largest improvements can be in athletes that have a lower fitness level because they are less efficient and rely heavily on carbohydrate stores for energy. Read more
Livers of trained subjects are also better at being able to convert lactate and amino acids to glucose that can allow higher levels of blood glucose levels during exercises (22). This means that untrained athletes have to take their energy from carbohydrate stores (either stored or taken on board through energy drinks etc).As a general rule of thumb, we would advise the following:
- Activities under 90 minutes in duration can be sustained without depleting your energy stores (carbohydrates) sourced from dietary intake. However, the body will need rehydrating and the electrolytes (sodium, calcium, potassium and magnesium) in your system replacing, during and afterwards. This is where an electrolyte sports drink can help instead of water. See question on Electrolytes (below).
- Activities 90 – 120 minutes in duration will begin to deplete carbohydrate stores and energy levels / performance may drop. If your carbohydrate levels continue to decrease, so that your muscles are forced to rely on fat for fuel, it is commonly referred to as ‘bonking’ or ‘hitting the wall’. Your focus should be on hydration and energy replacement throughout. By taking on carbohydrate in the early – mid stages of the session, your body should be able to call on this energy towards the latter stages and therefore avoid the drop in energy / performance. Additionally, this will assist in improving how you feel, post-exercise.
- If you take part in longer events, you should already have some knowledge of what works best for you, in terms of staying hydrated and fuelled for the duration. Again, your focus should be on hydration and energy replacement and there are a variety of ways of achieving this ranging from solid energy food to energy gels to powder drinks. You will need to invest some time into researching what works for you. Hydration is important but there will be a limit as to how much liquid you can take on board before potentially feeling bloated. Energy gels are a good way of topping up carbohydrate stores without having to ingest so much water. Solid foods are another good way of topping up carbohydrate stores without the extra water intake, but they can be cumbersome to carry if running, for example.\
Q: WHY DO I NEED ELECTROLYTES? WHEN DO I TAKE ON NUTRITION?
A: At a purely scientific level the electrolyte minerals, sodium and potassium, are involved in conducting electrical signals to/from muscles; calcium and magnesium are essential for the contraction and relaxation of the muscle fibres. These minerals work together to maintain normal electrical potentials and to coordinate muscle contraction/relaxation. Dietary basics are essential, but depending on your sporting activity and environment, maintaining optimum hydration, electrolyte balance and muscle glycogen levels may require assistance in the form of purpose designed sports drinks. Read more
In hot and humid conditions, sweat losses can be considerable – even when the duration and intensity of exercise are fairly modest. In such conditions, the main priority is fluid and electrolyte mineral replacement. Some carbohydrate replacement is also advantageous.In cooler, less humid conditions and where the exercise duration is longer leading to significant reductions in muscle glycogen (for example over 1-1.5 hours), carbohydrate replacement becomes more of an issue, although fluid and electrolyte replacement is still vital.The question of when you take on fluid and electrolytes can differ greatly from person to person. It’s useful to know how much you sweat but generally thirst is a good indicator that you need to start drinking more.
Your sweat rate is the amount of fluid you lose, primarily through sweat, during each hour you exercise under your usual exercise conditions. It is also a guide for the amount of fluid you should usually consume each hour while exercising to stay well hydrated and perform your best.
Sweat Rate* = (A + B) / C
A – Weight lost (in grams) during exercise (under normal workout conditions)
B – Amount of fluid drank (in ml) during exercise (1 litre = 1000 ml; 1 gulp = about 30 ml).
C – Number of hours exercise
Sue drank 360 ml of fluid during her 1-hour workout and lost 1/4 kilo (250g).
Her sweat rate is:
[(360+250)/1] = 610 ml/hr. Therefore, to drink to her sweat rate, Sue should consume about 610 ml every hour — or about 150 ml every 15 minutes — during her workouts.
* For greatest accuracy, weigh yourself without clothing or shoes and avoid using the restroom prior to post-exercise weigh-in.
By using this formula, you can then tailor your nutrition plan accordingly.
You must begin your endurance event fully fuelled and ready. Then, armed with the knowledge that events over 90 minutes will require further fuel; ensure you take on this fuel, allowing for sufficient absorption time.
Correct hydration and fuelling strategies can be the key to a successful performance and avoiding feelings of lethargy and fatigue, post event. By researching all of the advice from a range of companies you can develop your own strategy and find a consensus of opinion on how and when to take on nutrition.
When running, the ability of the body to ingest as much fluid as you sweat is almost impossible. Most rates of ingestion have not been seen above 1.3L/hr without leading to bloating and discomfort. When cycling however this can be increased because of the lesser abdominal pressures (8). From a triathlete’s perspective, it is worth knowing your sweat rates for both cycling and running. If you can start the run hydrated, then the issues surrounding discomfort with large volumes of fluid becomes less.
Without replacing electrolyte content (in particular sodium chloride), replacing fluid levels is near enough pointless as it is these salt levels that control fluid retention.
It has also been shown that repeated ingestion of fluids (including some carbohydrate) increases the rate of gastric emptying (23) due to the fact the emptying rate is higher with a fuller stomach. In other words taking on board repeated quantities of carbohydrate, salts and fluid leads to a higher overall quantity absorbed; hence the ability for your body to develop hyponytraemia, where too much water is absorbed without substantial electrolyte replacement.
Q: I HAVE TO HAVE SOLIDS TO RACE; DO YOU NOT GET HUNGRY ON A LIQUID ONLY PLAN?
A: It’s perfectly acceptable to use solid foods too (especially if you need that full feeling in the stomach) but they take longer to digest and you still need to take on fluids to stay hydrated. But you may find that your digestive system handles gels better than solids, or vice versa. It may not even bother you that much at all and you can transition onto solid foods easily. Read more
If you’re training for an endurance event, it’s important to test different liquids and foods during your long training runs so you can know what works best for you. You don’t want to try anything new on race day. It is important to note that if you are consuming a high volume of fluids with adequate energy in them, then you will feel like you have eaten a lot, as there is still a high amount of substance there.
The other factor to consider is convenience. If you’re doing a race, you can always get sports drinks from the aid stations (as long as they have the product that you like and have trained with). But if you rely on just sports drinks during your long training runs, you may have to stop to get more along the way. If you use food, you’ll most likely be able to carry enough fuel for your entire run in your pockets or running belt, but you will also need to hydrate as well.
Studies have shown that solid fuel was equally as effective, over a 3 hour aerobic cycling session, as liquid / gel fuel (24)(25)(26)(27)(28). However, similar studies undertaken, using triathletes, showed that once running is introduced, the liquid / gel fuel performance far surpassed the solid fuel nutrition, due to the jarring and sloshing motions exerted on the body.
Q: HOW DO I CARRY MY NUTRITION, PARTICULARLY ON LONGER EVENTS?
A: When cycling, it’s easiest to carry your drink in bottles on the bike. Gels and bars can be carried in the back pockets of a cycling jersey or in small “Goodie Bags” which sit on the top tube. For running it is more difficult but there are a few products ‘out there’ that try to address this issue like gel belts, running bottles, gel/utility belts, bum bags, Camelbak®, plastic gel bottles, running vest (more for ultra events) or simply carry the nutrition in shorts/tops with pockets. This will come down entirely to personal preference, and as with the nutrition strategy itself, requires practice during training to find out what works for you. Read more
Q: THERE IS A LOT OF SALES INFORMATION OUT THERE – HOW DO I KNOW WHAT IS TRUE AND WHAT IS NOT?
A: Try to find a consensus of opinion in the wider arena, prior to deciding which companies’ products you will try. It is very important that you know and understand how your body works and reacts to exercise before you find a successful way to apply sports nutrition to it. E.g. sweat rate, how you react to heat/cold or higher altitudes etc. Read more
Q: IS CAFFEINE A DIURETIC? CAFFEINE DURING RACES.
A: It has been shown that caffeine can enhance vigilance (focus) during bouts of extended exhaustive exercise. Caffeine is ergogenic (performance-enhancing) for sustained maximal endurance exercise, and has been shown to be highly effective for time-trial performance. Caffeine supplementation is beneficial for high-intensity exercise, including team sports such as football and rugby, both of which are categorised by intermittent activity within a period of prolonged duration. Read more
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