Dehydration hurts performance, right? Not necessarily. But don’t ignore it.
Pro racers ride so hard their guts can’t absorb enough fluid to replace all that they sweat out. Race rules may restrict when a rider can get a bottle toward the end of a stage. Although somewhat dehydrated, the pros sprint quite well! Despite the dehydration pro, we rarely read about cramps in the peloton. In lab experiments, dehydration has not been shown to cause cramps.
We’ve all seen pictures of runners collapsing at the end of a marathon or triathlon. Must be because the runner is dehydrated, right? Wrong. When an athlete stops, the runner’s pulse and blood pressure fall significantly so less blood gets to the brain and the runner faints.
For more read my column on 12 Myths About Hydration.
The average male’s body is 60% water; the average female’s is 50%. The typical athlete has another 10% water because glycogen is stored with water. If we don’t replace most this, we die. However, almost all of the heat-related deaths every summer are shut-ins living in homes with no air conditioning. Your body has about 2 quarts (liters) of free water in your intestines. You don’t even start to feel thirsty until you’ve lost 1.5 to 2 quarts of water!
The American College of Sports Medicine recommends avoiding dehydration of more than 2%, i.e., 2% of your weight. If you weigh 150 lbs, then 2% dehydration is three pounds. Three pounds is about 1.5 quarts of water.
Physicians, scientists and coaches now recommend drinking enough to satisfy your thirst, not significantly more. Joe Friel recommends: “Pay attention to your thirst mechanism. Drink when you are thirsty. When you’re not thirsty, don’t drink. It’s that simple.” [The Cyclist’s Training Bible (2009) page 257]
If you drink when you’re thirsty you won’t get more than 2% dehydrated.
For more read my column on Anti-Aging: Why “Drink Before You’re Thirsty” May Be Dangerous.
Aging and dehydration
The Mayo Clinic says, “As you age, your body’s fluid reserve becomes smaller, your ability to conserve water is reduced and your thirst sense becomes less acute. These problems are compounded by chronic illnesses such as diabetes and dementia, and by the use of certain medications.” Mayo Clinic dehydration symptoms and causes
Last December I tried to ride up Berthoud Pass (11,300 ft.) I live at 9,000 ft., so the altitude wasn’t much of a problem. I made it to about 11,000 ft. and passed out. My bike and I rode in an ambulance to the hospital. After echocardiograms, blood tests and a treadmill stress test the cardiologist concluded nothing was wrong with me — except I was dehydrated. As I got more dehydrated while climbing my blood volume decreased and my blood pressure dropped. So I passed out.
You can read more about my misadventure here Anti-Aging: Avoiding Dehydration
Signs of dehydration:
- Thirst. This is the most obvious; however as noted above the thirst mechanism becomes less acute with aging.
- Skin test. Pinch and release the skin on the back of your hand or forearm. If your skin stays pinched for a few seconds instead of immediately becoming normal, then you probably need more fluids.
- Urinating. If you’re not urinating every two or three hours you probably need more fluid. However, dark urine isn’t a sign of dehydration. Dark urine can result from supplements your body is excreting.
- Mood swings. Studies suggest even mild dehydration could make you more irritable and even anxious.
- Lightheadedness. If you feel dizzy after standing up, you are probably are dehydrated. You get dizzy or lightheaded when your brain isn’t getting enough blood. As you get dehydrated the volume of your blood decreases lowering your blood pressure causing lightheadedness.
[New York Times 5 Signs You Might Be Dehydrated]
If you have any of these signs get more fluids until the signs go away. In addition to beverages, oranges, strawberries, watermelon and even lettuce are primarily water.
Here’s another useful article: “If there is one health myth that will not die, it is this: You should drink eight glasses of water a day. It’s just not true. There is no science behind it.” Aaron E. Carroll M.D. No, You Do Not Have to Drink 8 Glasses of Water a Day
- Heat Tolerance and Aging
- Anti-Aging: Muscle Cramps
- What Should a Beginning Cyclist Eat and Drink, part 1
- What Should a Beginning Cyclist Eat and Drink, part 2
- An Effective and Low-Cost Homemade Sports Drink
My eBook Anti-Aging: 12 Ways You Can Slow the Aging Process includes information specifically for older cyclists on all of the different physiological changes with aging and how you can mitigate the changes. The 106-page eBook is available for $14.99.
Cycling in the Heat Parts 1 and 2 bundle:
You can learn more about the science of riding in the heat, and managing your fluids and electrolytes, in my two-part eArticle series:
Cycling in the Heat, Part 1: Ride Management is 19 pages and covers
- Why you get hot while riding
- Effects of overheating
- Acclimating actively and passively
- How to train in hot months
- How to ride without overheating in all conditions
- How to stay (relatively) cool while riding
- What to wear in the heat
- What to eat and drink in the heat
- How to cool down if you overheat
- Heat-related problems
Cycling in the Heat, Part 2: Hydration Management is 21 pages and covers
- Assessing your sweat rate and composition
- How much should you drink?
- Fluid replacement
- Electrolyte replacement
- Electrolyte replacement drinks
- Electrolyte replacement supplements
- Electrolyte replacement food
- Hydration-related problems
The cost-saving bundled eArticles totaling 40 pages Cycling in the Heat Parts 1 and 2 are just $8.98 (a 10% savings)
Coach John Hughes earned coaching certifications from USA Cycling and the National Strength and Conditioning Association. John’s cycling career includes course records in the Boston-Montreal-Boston 1200-km randonnée and the Furnace Creek 508, a Race Across AMerica (RAAM) qualifier. He has ridden solo RAAM twice and is a 5-time finisher of the 1200-km Paris-Brest-Paris. He has written over 40 eBooks and eArticles on cycling training and nutrition, available in RBR’s eBookstore at Coach John Hughes. Click to read John’s full bio.
Kerry Irons says
My own experience is that thirst is not a good indicator for me. I’m old now but it was the same many years ago. I learned to drink based on the ride itself: distance, temperature, humidity, and how well hydrated I was when starting the ride (based on morning weight). Your check for hydration can be either weighing yourself as you leave and when you get back (retrospective), having to pee every 2-3 hours or so during the ride (concurrent), or keeping track of past rides and how much you drank and drinking more this time (prospective). It never hurts to down a glass of water just before you get on the bike . NOTE: if you’re short on electrolytes, you’ll be peeing like a race horse and the water will just go right through you or it will slosh around in your stomach and you’ll want to barf.
Agree with everything Kerry says, except that I’m a slow learner. 🙂
What he says about low electrolytes seems counter-intuitive. Who would have thought a slug of salt (pill, electrolyte formula, etc.) would settle a sloshing stomach? Or when you have to pee and you’re horribly thirsty that salt’s the answer to your problems? But both of those are true IME.
As a sort of experiment, I have been going on 2 hour rides first thing in the morning. When I say first thing, I mean I get out of bed, go to the bathroom, get dressed, grab my water bottle, and get on the bike. While on the ride, I drink somewhere around 30 oz of water. When I get home I’m tired but feel okay. I drink two little protein shakes (10 oz each), a full water bottle (30 oz), and have some kind of energy/breakfast bar.
After sitting for 30-45 minutes cooling down and consuming the above, I have found that I am really dizzy. On a recent ride, I stopped near the end to drink a little water and ended up talking to someone else that had stopped for probably 10 minutes and started to have this same dizziness. I was able to start pedaling and get the mile or so home without issue, but after the routine above I still had some dizziness. It seems to be the worst when I bend over, like when taking off my shoes or for whatever other reason.
I thought maybe it was dehydration, but even with drinking roughly 50 oz of fluids this still happens. Yes, it takes some time to absorb the consumed fluid, but this feeling can last for a few hours to most of the rest of the day. At first I was not eating the energy/breakfast bar when I drank the fluids and this seems to have helped but not stopped it. I am trying to lose some weight, which is to say that I am not a thin person and the primary reason I have been doing this experiment. I just wanted to burn some calories before putting any in.
I have also measured my blood pressure a few times after a ride. It is sort of high when I first get home and then settles down after 10-20 minutes. When the dizziness happens though it seems that the blood pressure has dropped quite a bit below my normal.
Big Ring Bob says
Not part of this discussion, but dealing with feeling thirsty. On a hard ride, 100K or more, in the last hour or more, I can become thirsty. I can consume several bottles of water, but the thirst does not go away. However, I have learned that if I drink a regular Coke, the thirst goes away. I suspect the thirst is being caused by low blood sugar. I also have noticed that I can “bonk” with this sensation of thirst. Ingesting some carbs solves that issue. I my case, the Coke is usually good for about 45 minutes to an hour of additional riding if I do not consume other fluids and carbs.