**3.3 Sports drinks and nutritional supplements: manipulating the internal environment**

Fluid and electrolyte replacements are another area in which sports science has focused on improving endurance running. Electrolytes lost through sweating in a long race include sodium and chloride -in high concentrations, and potassium, magnesium, and calcium in low concentrations. All these electrolytes are essential as they work together to maintain fluid balance in the body at rest and during physical activity. Buffering acidosis is another crucial role of electrolytes such as sodium bicarbonate, thus regulating acid–base balance (blood pH) [61]. Therefore, it is important to replace any lost electrolyte in order to maintain a stable internal environment for optimal metabolic processes. This is recommended for high-intensity exercise with an extended duration of more than 61 min, where heavy sweating is expected, especially in environmental conditions of high ambient temperature and humidity. Moreover, replenishing fuels, in the form of blood glucose, are important for such exercise in order to avoid early fatigue and exhaustion. In this case, it is recommended to athletes to take sports drinks or nutritional supplements that top up carbohydrate reserves and electrolytes during and after long runs [62, 63]. Sodium in a sports drink helps the body absorb and retain body fluids, and utilise

carbohydrate. Endurance-specific electrolytes and calorie sports products such as the First Endurance Electrolyte Fuel System (EFS), Gatorade Endurance Formula, Luna Electrolyte Splash, Hammer Motor Tabs, and Powerbar Endurance Sports Drink are designed to offset higher losses of fluids and electrolytes through heavy sweating associated with muscle cramping [62]. There are also supplements such as beetroot juice, caffeine, and glycerol, which are said to boost performance and help the body cope with the demands of marathon training. However, their effects vary among athletes and may depend on training content, physical condition and habits [64].

Recent advancements in sports drinks seem to have triggered a fuelling revolution in the use of hydrogel technology by Maurten, the company that brought a new kind of sports drink mix and gel to the market in 2017. The Maurten sports drink has been widely embraced after being used by high-profile athletes -including Eliud Kipchoge in 2017, when he set a new marathon record twice, as well as in his epic trials to break two-hour barrier [65–67]. For many years, nutritionists and exercise physiologists have recommended that marathon runners consume no more than 45–60 g of carbohydrate per hour. Taking in more has been associated with increased risk of bloating, nausea, diarrhoea, and other gastrointestinal problems that affect 30–50% of runners [67]. However, some researchers believe that higher carbohydrate intake would likely result in better performance than lower intake in events lasting longer than two hours [65, 67]. In 2015, Maurten seemed to make a breakthrough when he discovered a way to encapsulate carbohydrate molecules using hydrogel technology. This is said to allow carbohydrates to move through the acidic stomach and to the intestines, where they can be absorbed more easily and help sustain performance. This lets one fuel more by taking in more calories without increased risk of gastrointestinal problems, and enable one to perform better in the race [65–67]. It is important to note that there are no empirical data so far that scientifically validate this notion. The product company website indicates that a number of studies are currently evaluating their technology and products and they are expecting that the first peer-reviewed paper will soon be published in support of their technology [66]. This will be necessary, just as with many other products of this nature, to reassure the users of the efficacy and safety as well as to dispel the notion of commercial interest as the key force behind the product's popularity.
