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As the temperatures climb, hydration strategies become significantly more important. Higher environmental temperatures place greater stress on the body during exercise causing a whole host of issues, including an increase in sweating. If higher sweat rates are combined with incorrect fuelling strategies, then the risk of dehydration is dramatically increased. This can lead to unwanted cramps or the common occurrence of hitting the wall.  

Although sweating is a great mechanism for cooling the body down, fluid loss equating to > 2 % body mass (1.4 kg in a 70 kg person) is enough to negatively impact performance. So, what negative impacts can dehydration cause?  


  • Increased body temperature
  • Increased heart rate
  • Increased glycogen (carbohydrate) usage in the muscles 
  • Increased perceived effort whilst working at the same exercise intensity 
  • Early fatigue 



Athletes can lose up to 1-2 litres of sweat per hour during moderate to high-intensity exercise and this is greater in warmer temperatures. Sweat consists of fluid (from the blood plasma) and electrolytes (including sodium, potassium, magnesium, chloride, and calcium), both of which are important for the body’s optimal functioning. Of the electrolytes lost, sodium has the greatest importance for exercise performance. 

Sodium is required for regulating fluid balance, assisting in controlling blood pressure and for the normal functioning of muscles and nerves. Sodium added to fluids consumed during exercise: 

  • Increases palatability 
  • Increases fluid absorption and retention 
  • Stimulates thirst, promoting the action of drinking 

These factors combined effectively reduce the risk of dehydration. The concentration of sodium in the bloodstream is regulated within the narrow range of 135-145 mmol/L. However, if only plain water is consumed whilst sweating (losing fluid and electrolytes) at a considerable rate then plasma sodium concentration is diluted. In addition to the above consequences of dehydration, this reduces cognitive performance and concentration, which are key elements for cyclists and triathletes. SiS HYDRO is the ideal solution for ingesting sodium pre, during or post-exercise. 


SiS HYDRO is a highly practical effervescent tablet that readily dissolves in water and contains electrolytes, vitamins, and minerals. This is ideal for replacing electrolytes lost through sweat, most importantly sodium. The tablets are easy to carry and can simply be mixed with 500 ml plain water to make a flavoured, easily consumable fluid, whilst also appropriately meeting your specific sodium requirements (amount: 0.7 grams per L, concentration: 30mmol/L).  



  • Exercise type, duration, and intensity 
  • Environmental temperature 
  • Individual traits e.g., body weight, age etc. 

However, in the summer months when environmental temperatures are higher and sweat rates dramatically increased, the importance of consumption significantly increases. 



Pre –A simple yet effective hydration strategy is to consume 500 ml of SiS HYDRO 3-4 hours prior to an event then an additional 250-500 ml in the 2 hours before. This will ensure you are hydrated on the start line. 

During –During the event, the primary aim is to prevent thirst and dehydration, which often equates to 500-1000 ml per hour, with thirst indicating whether more is required. If the environmental temperature is high, this value is likely to increase because of greater sweat rates.   

Post – The aim post-exercise is to replace fluid lost through sweat. The best way to do this is to measure body weight before and after exercise, and for every 1 kg lost through sweat 1.5 L of fluid should be ingested. This should be consumed gradually over the hours post-exercise to avoid gastrointestinal discomfort. 


British 2022 Commonwealth Games 10,000m champion, Eilish McColgan, often trains and competes through the summer months when temperatures are at their highest. The Science in Sport team caught up with Eilish to get her top tips for managing the heat:  

  • Make sure you hydrate, not only with water but with Science in Sport electrolytes too. Just a small drop in hydration can have a big effect on performance. My favourite flavour is strawberry and lime. 
  • Wear a visor or cap to help stay cool and keep the sun off your face. Sometimes, I put my visor in the freezer or in cold water before I head out the door.
  • Stick to light coloured and breathable clothing. Black absorbs the heat – making you feel warmer.
  • Choose shaded running routes. A park or woodland area will always be a few degrees cooler than running around the streets. 

 If you are training for a longer duration and need additional carbohydrates, then incorporating SiS GO Electrolyte powder or GO Energy + Electrolyte Gels can be an efficient way to replenish the body with what it needs.  

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