A reader asked me to discuss the importance of hydration during workouts, especially CrossFit workouts.
I've long been of the unsubstantiated opinion that the human body can tolerate a fairly wide range of hydration levels. Kidneys are a pretty neat little organ and from a physiological standpoint and they do a pretty fantastic job of maintaining homeostasis, so long as you don't overdo it in one direction or the other. However, from a sports standpoint, what exactly should we be doing?
1. How do we lose and gain water?
Water is lost via perspiratory, respiratory, renal, and gastrointestinal processes. In English, you lose water by sweating, breathing, peeing, and pooping.
Water is gained from consumption and metabolic processes. In English, your body gains water by drinking and by simply being alive.
Typically, the net water turnover from respiratory and metabolic processes is fairly close to zero, whether at rest or not.
Peeing is obviously a loss of water, but water excreted by the kidneys has arguably already exited your body, so it doesn't "count" per se. Furthermore, renal activity greatly reduces during exercise, as the body naturally mobilizes itself for a protracted period of sweating and elevated metabolic needs.
Normal poop contains very little water, so water loss from bowel movements is minimal (exception: diarrhea). Intestines do a pretty fantastic job of eking out every bit useful nutrient, including water, from the food you ingest.
Therefore, the primary source of water loss is sweating.
2. How much sweating is too much sweating before athletic performance degrades?
The ACSM asserts that >2% bodyweight loss of water is a "critical water deficit" that degrades aerobic exercise potential, citing higher core body temperature and higher heart rate as the main reasons for degradation. The same article also suggests that the marginal decrement in aerobic performance is minimal as loss of water continues; it's mostly an all-or-nothing bodily response. Note that >3% is considered clinically dehydrated. Lastly, the article suggests that neither muscle strength nor anaerobic capacity are significantly impacted by hydration levels.
I haven't weighed myself in quite some time, but assuming I am still roughly 157 lbs, a 2% loss of water is approximately a 48 oz water deficit, or 3 full pints of water. That's an enormous amount of water to lose to sweating and I would suspect that an hour of exercise at varied intensity is not sufficient to cause such a deficit, but I don't want to assume too much. Which leads to my next question...
3. How quickly does a person lose water to sweating during exercise?
Obviously, sweat rates can vary greatly according to activity, individual physiology and a huge number of environmental factors. The article's observations show sweat rates for a variety of sports (rowing, soccer, football, tennis, triathlon, etc.) and range from 0.5 to 2.0 L/h, or 17 to 67 oz per hour.
So there you have it. Depending on circumstances, it's quite possible to lose enough water during a one-hour workout to yield sub-optimal aerobic performance. Combined with the relatively common incidence of beginning a workout while partially dehydrated, it is quite possible that insufficient hydration could be a factor.
4. Okay, so what should we do?
To keep it simple, here is what is generally recommended:
I've long been of the unsubstantiated opinion that the human body can tolerate a fairly wide range of hydration levels. Kidneys are a pretty neat little organ and from a physiological standpoint and they do a pretty fantastic job of maintaining homeostasis, so long as you don't overdo it in one direction or the other. However, from a sports standpoint, what exactly should we be doing?
1. How do we lose and gain water?
Water is lost via perspiratory, respiratory, renal, and gastrointestinal processes. In English, you lose water by sweating, breathing, peeing, and pooping.
Water is gained from consumption and metabolic processes. In English, your body gains water by drinking and by simply being alive.
Typically, the net water turnover from respiratory and metabolic processes is fairly close to zero, whether at rest or not.
Peeing is obviously a loss of water, but water excreted by the kidneys has arguably already exited your body, so it doesn't "count" per se. Furthermore, renal activity greatly reduces during exercise, as the body naturally mobilizes itself for a protracted period of sweating and elevated metabolic needs.
Normal poop contains very little water, so water loss from bowel movements is minimal (exception: diarrhea). Intestines do a pretty fantastic job of eking out every bit useful nutrient, including water, from the food you ingest.
Therefore, the primary source of water loss is sweating.
2. How much sweating is too much sweating before athletic performance degrades?
The ACSM asserts that >2% bodyweight loss of water is a "critical water deficit" that degrades aerobic exercise potential, citing higher core body temperature and higher heart rate as the main reasons for degradation. The same article also suggests that the marginal decrement in aerobic performance is minimal as loss of water continues; it's mostly an all-or-nothing bodily response. Note that >3% is considered clinically dehydrated. Lastly, the article suggests that neither muscle strength nor anaerobic capacity are significantly impacted by hydration levels.
I haven't weighed myself in quite some time, but assuming I am still roughly 157 lbs, a 2% loss of water is approximately a 48 oz water deficit, or 3 full pints of water. That's an enormous amount of water to lose to sweating and I would suspect that an hour of exercise at varied intensity is not sufficient to cause such a deficit, but I don't want to assume too much. Which leads to my next question...
3. How quickly does a person lose water to sweating during exercise?
Obviously, sweat rates can vary greatly according to activity, individual physiology and a huge number of environmental factors. The article's observations show sweat rates for a variety of sports (rowing, soccer, football, tennis, triathlon, etc.) and range from 0.5 to 2.0 L/h, or 17 to 67 oz per hour.
So there you have it. Depending on circumstances, it's quite possible to lose enough water during a one-hour workout to yield sub-optimal aerobic performance. Combined with the relatively common incidence of beginning a workout while partially dehydrated, it is quite possible that insufficient hydration could be a factor.
4. Okay, so what should we do?
To keep it simple, here is what is generally recommended:
- Hydrate immediately before your workout. 12-16 oz will usually suffice.
- Every 15-30 minutes during your workout, take a drink. It could be anywhere from 5-20oz, depending.
- After your workout, be sure to drink consistently for the next 4-6 hours.
It is very uncommon to find an athlete that maintains pre-workout water levels throughout his or her training. Drinking fluid after a workout to replace lost fluids is critical. Recall that sweating continues well after a workout, but also that peeing resumes. While a normal person is unlikely to know their total water loss for a given workout, it doesn't hurt to keep sipping water for a few hours post-workout.
I know that I need to up my water intake, both inside and outside the gym. I won't be able to measure improvements because of this change, but relative to the effort I need to put forth elsewhere, this is by far the easiest way to get a small gain in athletic performance.
I have been having weird breakdowns during my workouts lately, and I have a strong suspicion that dehydration is the cause.
ReplyDeleteThree times while circuit training I started feeling feverish and terribly weak. Thought I was having a surprise attack of the flu.
This past week I did a stair workout (just going up from my floor, 25, to the 43rd floor, trying to be as explosive as I can)... between 41 and 42 my legs just gave out and I felt like I was going to faint. I sat down, and my legs got the most significant pump they've ever had. Unlike a normal pump, however, this one persisted and grew, despite my total ceasing of exercise. I couldn't stand up, so I crawled on my butt down the stairs to the 41st floor landing. Still couldn't stand and still thought I was going to pass out, so I lied on back. Leg pump still was not going away after 5 or so minutes but I felt strong enough to try standing. Was able to take the elevator back down to my office. Scary experience though. I drank a ton of water that day but also peed a ton. Whatever it was, I'm not too interested in repeating it. Was a pretty good pump though.
Sounds to me like you might have hit your anaerobic threshold or depleted your glycogen stores, or both. Better hydration will somewhat improve your body's capacity to metabolize lactic acid, but if I just had to guess, you burned up your glycogen in short order because you didn't eat enough.
ReplyDeleteEat regularly and eat higher quality food. Always drink some water before you begin a workout.