Alf Tupper, Tough of the Track, may have been able to beat all-comers on a diet of fish and chips, but these days the kids rock to the beat of isotonically balanced Maltodextrin solutions. If you're anything like us, the only thing you know about sports drinks is that their adverts tend to be intensely annoying. To remedy that, we've got Victoria Richmond on-board as our Sports Supplements specialist. If you've got a question about food and drink supplements, you can drop her a line via [email protected]. Below, she writes about how to maximise hydration and energy supply during exercise:There are two critical nutritional factors that affect sports performance. The first of these is hydration. As little as a two percent loss in body weight through dehydration can decrease performance by up to 20 percent. The most serious effect of dehydration from failure to replace fluids during exercise is impaired heat dissipation, which can elevate core temperature to dangerously high levels. Dehydration also causes a reduction in plasma volume, which in turn results in a decrease in cardiac output, thus compromising cardiovascular function.When dehydration is a problem there is more to consider than simply the loss of water. Mineral loss may also occur as a result of excessive sweating, especially when training indoors or in humidity. The main minerals are sodium, potassium and chlorine. These are collectively called electrolytes because they are dissolved in the body as electrically charged particles called ions. Excessive loss of these electrolytes can lead to severe dysfunction in the form of heat cramps, heat exhaustion, or heat stroke. The second nutritional factor to consider during exercise is energy supply. During light and moderate exercise about half of the body's energy requirement is supplied by carbohydrates and, once carbohydrate energy is used up, performance decreases by about 50 percent. Taking onboard fluids before and during exercise reduces the detrimental effects of dehydration on cardiovascular dynamics, temperature regulation and exercise performance. The main aim of fluid replacement is to maintain plasma volume so that circulation and sweating can progress at optimal levels. By adding carbohydrate to the oral rehydration solution, additional energy for exercise is provided as the endogenous carbohydrate becomes depleted. The rate at which fluid balance is restored and carbohydrate is available for utilisation is determined by the rate at which ingested fluid empties from the stomach and is absorbed into the blood. This can be enhanced by consuming sports or energy drinks as opposed to water, but there are so many types which one should you choose?There are three classes of energy drink:Hypotonic - contains fewer molecules in solution than the body's fluid.Isotonic - contains approximately the same number of molecules as body fluids.Hypertonic - contains more molecules than body fluids. These tend to be heavy on the stomach and the rate of gastric emptying is slow. Sugary drinks are hypertonic and have a negative effect on water absorption.It is important to meet both carbohydrate and fluid requirement and it is possible to consume a carbohydrate-electrolyte solution without compromising water absorption. Adding a small amount of glucose and electrolytes to the oral rehydration solution has only a small negative effect on gastric emptying and may actually help fluid uptake once inside the intestine. The glucose contributes to the maintenance of blood glucose and the main electrolytes (sodium and potassium) may help enhance intestinal water absorption. There are many different types of sport drinks specifically for consumption before, during or after exercise. Drinks for pre-exercise and also during exercise are lighter on the stomach and will often contain Maltodextrin as the main source of glucose and contain electrolytes for rapid absorption. Post-exercise fuel will contain more complex carbohydrates as well as protein to facilitate recovery. These are heavier on the stomach and therefore not so suitable for consumption during exercise. Concept 2 sells a wide range of Science in Sport supplements, available on the website at: http://www.therowingcompany.com/shop/food_supplements.php. If you've got any questions about either them or sports supplements in general, send an email to [email protected].