Hydration and Electrolytes

Seeing that the human body is made up of around 60% water, it is essential that you keep your body well hydrated during your training and the marathon itself.

As you exercise, your body heats up just as the engine in a car heats up during a journey. To stop overheating, water is drawn for blood plasma and secreted from pores in the skin, as sweat, to cool the body down. However, as the water content of blood decreases, it changes from a free flowing watery substance into a thicker more “treacle” like substance. This makes it harder for blood to flow through the arteries and veins quickly enough to supply the muscles with the right nutrients to sustain the same level of exercise.

To meet the demands, the heart is forced to pump faster, resulting in an increase in heart rate. This ultimately leads to feelings of fatigue and premature exhaustion. Just a 1% decrease in hydration, will cause around a 5% decrease in performance. A water loss of just 12% of a person’s body weight can lead to death.

To hydrate the body effectively during exercise, it is important that you take on more than just water. An “isotonic” sports drink will not only contain 7-10% glucose, but minerals such as sodium and potassium, known as electrolytes.

When we sweat, as you can tell by the taste, we lose salts from the body. This loss over a short run is not generally a problem as the body has hormonal regulators to balance the salts in our cells to keep them normal. However, during longer runs salt loss from the body can lead to a potentially life threatening condition known as “hyponatremia.”

Hyponatremia occurs when sodium levels drop too low leading to symptoms of confusion,
weakness, disorientation, even seizures. Luckily, cases of hyponatremia are rare, but they do happen in marathons. There is no need to go overboard on salt consumption in the lead up to the race, as we all consume too much salt in our diets anyway, but it is certainly not a good idea to completely avoid salty foods.

During training runs, make sure your fluid replacement drink contains both sodium and glucose. If possible, try to plant drinks on your planned route, such as by a tree, so that you don’t have to carry heavy bottles with you.

During the marathon, Gatorade sport drinks are provided at 5 different points. To keep your glucose and salt levels up, make sure you take a drink at these designated points.

Once again, it is important that you practice drinking the sports drinks during your training. This is not only to get used to drinking on the run, but also to make sure your system is not intolerant to the drinks. Avoid drinking them all in one go: sip regularly and, if possible, wash the drink down with water too. By Graeme Hilditch