Recovery and Water

Recovery and Water

By: Nick Soleyn, PBC, Editor in Chief

Thirst is a powerful motivator. It is a response to homeostatic controls designed to keep you alive. If you recall, your body maintains homeostasis in various systems through a simple process: Receptors sense stimuli and send information to a control center, which then sends signals to effector cells, muscles and glands, that can cause a physical response to help your body restore balance. The amount of water in your body is one of the most finely controlled balancing acts of your autonomic nervous system. This is pretty impressive when you consider how much water makes up “you;” it is the most essential of essential nutrients. We should care about thirst because, unlike most other unconscious bodily functions your hydration requires your constant, active participation.  

Thirst is your body’s signal that it needs help restoring or maintaining its fluid balance. Fluid balance is the ratio of water to the electrolytes that carry the electrical impulses that allow your brain to direct your cells. Your body is made up of about 60% water, stored either inside your cells or outside of them. Inside your cells (the intracellular compartment) water is part of the fluid used for all chemical reactions. Outside of the cells (extracellular compartment), water is part of your plasma that transports salts, proteins, nutrients, gasses, and wastes around your body, and which can then travel between cells via the interstitial fluid stored around cells. About two-thirds of your total water content is in intracellular compartments and one-third will be stored in the extracellular compartments, partially in your plasma but mostly in the interstitial fluid, or the fluid that surrounds your cells. Water moves between the intracellular and extracellular compartments via osmosis.

When the concentrations of water and electrolytes are stable, then these compartments are stable. There would be no need for fluid to move between intracellular and extracellular compartments. But, fluid balance is a dynamic state. Because you are constantly using, creating, and losing fluid, making you in more-or-less constant need of replacing it.

Ideally, water lost should be equal to water intake, but this isn’t as simple as it may sound. You lose water through both fixed and variable processes. Fixed water losses are through your stool, sweat, and breathing, each possibly ranging from 0.1L/day to 0.3L/day with big variations depending on activity levels and health. These fixed losses are difficult to measure outside of a lab or without some curious personal measuring habits.

You lose a lot more water when you urinate, averaging between 1.0 and 1.5L/day, but this varies depending on your water needs as well, making it somewhat unpredictable and difficult to plan for. Water loss through urine is considered variable because your body’s water conservation processes happen there. Sensory receptors in the brain detect the electrolyte-water balance in your plasma. When the concentration changes, your body responds. For example, when you sweat, the water concentration in your blood goes down. This means that your plasma osmolality increases.

A decrease in plasma water triggers a few responses. The pressure itself causes some movement of water from the intracellular compartment to the extracellular, helping you maintain important functions like cardiac output. In addition, the osmoreceptors trigger the powerful thirst mechanism and the release of antidiuretic hormone (ADH)—both of which help regulate your fluid balance and prevent cellular dehydration.

ADH triggers the reabsorption of water back into the extracellular compartment. This happens through different pathways but occurs in the kidneys. This is why you may notice that your urine is darker in color when you’ve been sweating or have experienced some greater fluid loss. Some experts’ advise drinking to maintain light-colored urine as a way to prevent dehydration. However, darker urine does not necessarily mean that you are dehydrated, rather it signals that your body is doing exactly what it’s designed to do to prevent dehydration, reabsorbing some of the water you were going to flush out as waste anyway.

Thirst is a biologically directed behavior in which you crave potable fluids. It is an essential mechanism of fluid balance homeostasis, affecting not only your behavior but also your perception of water. Water tastes better when you are thirsty and is incredibly satisfying.

How Much Should You Drink?

OpenStax College [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]

Both perspectives have merit, but both rely on certain assumptions or outcomes that may be atypical for most people. The idea that you should drink to prevent thirst seems rational. After all, if thirst is a signal of a change in fluid balance, then wouldn’t it be better to just preemptively maintain the balance and keep your body happy? Probably. But as we noted earlier, how much you actually need would be difficult to measure and would change daily. Also, thirst isn’t as closely connected to the problems associated with dehydration as you might think. That’s because it isn’t the only a rehydrating mechanism your body has at its disposal. When your body pulls water out of your kidneys, it’s already restoring the balance. This is why water loss through your kidneys can vary so much. They act like a water reserve when you need it. Sure, you still need to replace lost fluid, but the fact that you are thirsty does not also mean you are experiencing the symptoms of dehydration. It just means that for some reason your body wants water, and you should listen to it. If you have ready access to water and are in normal conditions, you probably do not need to drink pre-thirst to survive. Our bodies are stubborn that way, you are not going to keel over just because you forgot your water bottle.

That said, just avoiding dehydration and death isn’t a great way to think about an essential nutrient, especially when we are considering water in the sense of it’s value to our recovery from training. As lifters, we are not just surviving, we are actively pushing our bodies out of homeostasis and fueling its recovery to get bigger, better, and stronger. Part of the discussion of hydration has to include our propensity to lift heavy objects, to sweat, and to recover. While normal fluid loss may be easily regulated and maintained through thirst, fluid loss, due to hot environments or high activity, occurs more rapidly. There remains a big question of whether exercise that promotes fluid loss should be anticipated and planned for by drinking more water prior to or during the activity.

The only possible downside to pre-thirst hydration is overhydration. And, in the extreme environments of marathons and long endurance races, overhydration seems to be a bigger problem than dehydration. Author Christie Aschwanden examined the history of marketing surrounding sports drinks and notes that overhydration is a widespread and dangerous problem, “There’s never been a case of a runner dying of dehydration on a marathon course, but since 1993, at least five marathoners have died from hyponatremia [(overhydration)] they developed during a race.” She also notes studies in which 13% of a sample of Boston Marathon finishers had diagnosable hyponatremia as did 10.6% of thousands of tested Ironman finishers.

These numbers suggest that overhydration is a concern worth considering. And while that’s true, it’s also circumstantial. The extreme loss of electrolyte concentration due to a lot of sweat loss and overhydration is a pretty specific mixture of factors. If you are running a marathon or will be sweating for hours on end, you should consider how you rehydrate and replenish your sodium through food. The dangers of overhydration do not tell us much about everyday needs. And the consequences tend to overshadow the relatively low risk of overhydration for the average person, even the average exerciser or the average person engaged in strength training. Overhydration is hard to achieve accidentally outside of marathon-like conditions.

For Lifters

As a lifter, you need to think about hydration the way any athlete does. Water helps preserve bodily functions and prevent negative physiological effects associated with dehydration. More is not better ad infinitum but neither is more harmful in normal circumstances.  A good minimum to start with is to drink half of your numerical bodyweight in pounds in ounces of water. The absolute minimum water consumption is half your body weight in ounces. If you weigh 200 pounds, that means at starting with least 100 ounces of water per day. If you feel thirsty, don’t panic. Just drink, and perhaps take note. While there’s no real benefit to waiting until you get thirsty to drink, there are some physiologic effects of dehydration that can occur asymptomatically. A moderately-defined water intake, adjusted up or down for your actual needs, which you adjust by paying attention to when you are thirsty, is a pretty good place to start.