Hydration
“When the well’s dry, we know the worth of water.” – Benjamin Franklin, Poor Richard’s Almanac, 1746
Water is needed to maintain blood volume, to allow the efficient transportation of nutrients and oxygen to tissues, and to regulate core body temperature by perspiration. Dehydration will lead to a reduction in blood volume, causing decreased skin blood flow, decreased sweat rate, decreased heat dissipation, increased core temperature and an increased rate of muscle glycogen use. This will leave you feeling nauseous, irritable, overly fatigued, with headaches and possible muscle cramps.
Exercise performance becomes impaired with just a 2% loss of body weight. Past 3% there is a significant drop off, and losses in excess of 5% of body weight can decrease the capacity for work by about 30%.
How much?
For a 75 kg athlete, 2% loss of body weight equates to 1.5 litres. Given that sweat loss can measure over 1 litre in a one-hour training session, it’s easy to see the importance of hydration, before, during and after exercise, for endurance athletes. A simple sweat test of weighing yourself before and after a one-hour workout (without drinking during) will give an approximation of your fluid loss – each 1 g of weight loss equates to 1 ml of fluid.
Not all the lost fluid needs to be replaced, however, and there is as much danger from over-hydrating (hyponatremia) as there is from dehydration – both have serious, potentially fatal consequences at the extreme. Thirst will indicate whether more or less fluid is required. Work on a principle of 75% replacement and you should get it right.
Weather conditions will clearly play a part, but assuming a loss of fluid equating to 1% of body weight, a 60 kg athlete will need to drink 450ml per hour, while heavier athletes nudging 80-90 kg will need 600ml plus. This will increase significantly in hotter climates but a bottle an hour is a good general guideline.
When and what?
Having established the need for hydration, the most obvious fluid replacement is water. A rough rule of thumb of 8 glasses (equivalent to 2 litres) of water a day is a good starting point although highly trained athletes should look to consume around 3 litres of water a day, plus whatever is required during training. This should be taken little and often throughout the day. Start the day with a cup of boiled water and a slice of lemon. Drink thereafter from a water bottle to measure daily intake and get a feel for the volumes required. Make sure that at least 500 ml is sipped in the hour or two before your workout, this should ensure that you are well hydrated before you start exercise and your body has time to get rid of the fluid it doesn’t need.
Whilst water may be an adequate choice for hydration, rarely will it be enough. A whole host of electrolytes are lost during the sweating process, sodium, potassium, calcium and magnesium being the main four. Of these, sodium is the key as it is essential in moving water around and maintaining fluid levels in the body. To maintain a healthy balance of sodium, and other essential nutrients, a hypotonic drink mix should ensure maximum absorption of electrolytes.
Ride Captains will mostly start with 2 bottles of a hypertonic electrolyte mix, switching thereafter to 1 bottle of hypertonic electrolyte mix and 1 bottle of pure water. Remember that this combination is low calorie and the standard nutrition plan outlined above must still be adhered to.