Studies have shown that surprisingly low fluid losses can significantly affect your ability to ride. A 2% decrease in body weight due to sweating (1.6 kg for an 80 kg rider) will significantly impair performance, 4% will decrease your capacity for muscle work, and at 5%, heat exhaustion can become a problem and your work capacity can decrease by as much as 30%. At 7%, you will begin to experience hallucinations and, at 10%, circulatory collapse, heat stroke and even life-threatening heat exhaustion become very likely.
The physiological reasons for loss of performance due to dehydration are:
- Reduction of blood volume
- Decreased cutaneous blood flow
- Decreased sweating rate
- Decreased heat dissipation
- Increased core temperature
- Increased muscle glycogen utilization rate
- Decreased digestive function
Hydration monitoring
Weigh yourself daily and, especially if you are already quite thin, a sudden and significant drop in weight probably suggests that you should increase your fluid intake. You can also monitor the color of your urine using charts like this one:
Daily drinking
Before considering what, when and how much to drink on the bike, make sure you stay well hydrated at all times which will mean maintaining optimal hydration levels when riding will be much easier. Monitor your hydration levels using the techniques mentioned above and try to drink 2-3 liters of fluids a day: water, juices, herbal teas, eating vegetables and fruits will make that goal easy.
And before an outing?
If you have been monitoring and maintaining your daily hydration, there should be no need to drink excessively the night before or in the hours leading up to a ride. In the two hours before a long ride, an intense training session or a Gran Fondo event, sip 500-750 ml of an electrolyte drink.
How much to drink on the bicycle
The best way to get an estimate of how much fluid you need to drink is to perform a 60-minute sweat test. Having hydrated well during the day, weigh yourself naked and note your weight.
Go out cycling at normal intensity for 60 minutes and do not drink during the ride. As soon as you get home, undress, wipe the sweat off your skin with a towel and weigh yourself again. The difference in the two weights in grams will equal the total fluid losses in milliliters.
Obviously, results will vary depending on weather conditions and ride intensity and you may want to run several tests to get an optimal range of readings, but it will still give you a good idea. Most cyclists will find that they typically lose between 500 and 1000 ml per hour. Especially if you are at the upper end of this range, it may not be necessary to try to recover all of it, but you should replenish a minimum of 75%.
When to drink on the bicycle
The key point to remember is not to wait until you are thirsty, but to drink little and often from the start of your ride. Aim for 2-3 drinks every 10-15 minutes right from the moment you start riding.
What to drink on the bicycle
For rides of less than 60 minutes, plain water is fine, but for longer rides or in hot conditions, you should add electrolytes. Plain water can cause you to feel bloated and will reduce your desire to drink before fluid losses have been replaced.
Electrolytes are salts that include sodium, potassium, calcium and magnesium. They are lost in sweat, are essential for normal cellular function and must be replaced. Most commercially available sports drinks have the correct balance of electrolytes but it is also very easy to make yourself a homemade sports drink with lemon juice, sugar, salt and a pinch of baking soda, which works just as well or better than commercial brands. Hundreds of homemade recipes are available online.
For longer rides, it makes sense to combine drinking with calorie intake. Remember: for a long training ride or a long distance ride, you will ingest 0.5-1g of carbohydrate per kilogram of body weight per hour and you should try to spread that out over 2-3 micro-drinks every 20-30 minutes. 500 ml of a typical isotonic drink mixed together will give about 36 g of carbohydrate, which, for an 80 kg cyclist requiring 40-80 g per hour, is a sufficient and easy to assume proportion of that energy requirement.
And on the roller?
The concept of hydration is exactly the same but with a peculiarity, sweating will be greater because the air will not cool our body in the same way as in the street no matter how many fans we put.
To find out how much fluid we lose we will do the one-hour test mentioned above, so we will know how much fluid to replenish in our roller sessions.
Can I drink too much?
In cycling it is somewhat complicated because the drink goes with us and it means refilling the bottles many times in order to reach hyperhydration. Supplementing the water with minerals will not cause any loss.
Does cramping occur due to dehydration?
Short answer: no. It is true that dehydration will not help, but there is no scientific evidence that cramps are caused by a lack of water or minerals (the magnesium myth), since the fundamental origin lies in fatigue and muscle overload, due to lack of training, doing work that we are not capable of and/or recruiting muscles that we should not due to incorrect technique or muscle weaknesses. If we are well hydrated and with good nutrition, cramps still appear in these cases.
