Tag Archives: hydration

The King of All Ergogenic Aids


by Sérgio Fontinhas. What’s the best ergogenic aid? Is it creatine? Caffeine? Vitamin D?

If you answered ‘water,’ then you’re clearly a Mensa member.women-water-12

The human body is approximately 60% to 70% water (with a range of 45-75%) (1). It can be is less with increasing body fat because fat is known as “anhydrous” with about 10% water, however fat-free mass can be 70-80% water (1). An average 70-kg person has approximately 42 L of total body water, with a range of 31–51 L (1). Improper hydration will result in either dehydration or overhydration (hyponatremia). Daily water balance depends on the net difference between water gain and water loss.

Individuals are routinely at a risk of mild dehydration day to day (2). Public surveys (10,11) and experimental trials (12,13) indicate that the general public, and most importantly special populations such as children and older adults, are at a risk of voluntary dehydration (14,15). Even experienced athletes can underestimate their hydration status and may drink insufficient amounts of water resulting in sustained dehydration (16).

Sustained dehydration is associated with poor health (3,4) and increases the likelihood of kidney stones and urinary tract infection by a significant degree (3,5). Additionally, prolonged vasoconstriction due to chronic dehydration increase the risk of hypertension and stroke (6).

An emergent body of evidence also suggests water consumption (and the food we eat) affect mental and physical performance (7). Water is essential to the maintenance of normal physical and cognitive function (8), and there are some recommended intake guidelines of 2000 ml of fluids for females and 2500 ml for males per day (9). More specifically it is recommended 3.7 L for 70 kg males and 2.7 L for 57 kg females (29).

Water is the medium of circulatory function, biochemical reactions, metabolism, substrate transport across cellular membranes, temperature regulation, and numerous other physiological processes (28). The loss or increase in fluids and electrolytes (potassium, sodium, calcium, magnesium…) affects cellular performance, and can cause cell death, and even death of the entire organism.

Assessing hydration status – Individuals should monitor their own hydration levels using markers such as urine color (27). Although dilution methods to determine total body water via plasma osmolality measurement are the most accurate, valid, and sensitive ways, they are not practical for most situations (30,122), but total body mass and urine color when used in conjunction is a good way to assess hydration status (30,122).

First-morning urine should look like pale yellow (27), indicating the normal and expected presence of some waste products from metabolism overnight. This color corresponds to a state of euhydration (34,35). I shouldn´t look at water, or anything dark.

Thirst is initially perceived when a body weight deficit of 1–2% exists (36,37), fluid consumption should be adequate to avert the perception of thirst. Thirst signals any imbalances of the osmolality of fluids and tissues (the electrolyte concentration), and the total amount of water in our body (volume).

Dehydration – Dehydration is characterized by weight loss, confusion, dry skin that is hot to the touch, and possibly an elevated core body temperature. In a hot climate, dehydration can be dangerous and result in thermal injury. Other causes of dehydration can be excess diarrhea, vomiting due to GI dysfunction, kidney disease, and diuretic medications.


Thirst may be a poor measure of hydration because of the lag between the physiological dehydration and the thirst signal. Special populations require more attention, elderly are less sensitive to the thirst mechanism the deterioration of osmoreceptor sensitivity in older adults (30,38,39,40,121); and children are inexperienced in interpreting the thirst response (41,42). Older adults are also at higher risk for reduced kidney filtration function, which results in less efficient water conservation (when dehydrated), further exacerbating difficulties in recognizing a dehydrated state (43).

Physiology of dehydration / physiological response

When the body is in a state of dehydration, many substrates and neurotransmitters are influenced by circulating vasopressin (antidiuretic hormone) and angiotensin II (44,45).  Dehydration can increase levels of cortisol (46). Interestingly, even a decrease in cell volume caused by hypohydration promotes insulin resistance (47,48,49).

Conditions dehydrating insulin target tissues such as hyperosmolarity or amino acid deprivation are associated with insulin resistance; blockage of the cell volume response to insulin may be the common denominator in dehydration-induced insulin resistance (47).

As a consequence of dehydration, the blood–brain barrier permeability is altered by serotonergic and dopaminergic systems, potentially causing central nervous system dysfunction if dehydration is prolonged (50).  Chronic dehydration influence inhibitory and excitatory activities of the brain by increasing aminobutyric acid and glutamate levels (51), by stimulating γ-aminobutyric acid and N-methyl-D-aspartate receptors, to synthesize and release antidiuretic hormone (56).

Even mild dehydration produces significant changes at the neural level: total brain volume shrinkage and over-recruitment of specific brain areas during cognitively demanding tasks (52).

Hypohydration and exercise

Hypohydration during exercise strongly rises the catabolic hormonal response to resistance exercise, and increase circulating concentrations of metabolic substrates. Hydration status during exercise changes the endocrine and metabolic adaptive responses to resistance exercise and also changes the postexercise internal environment. Specifically, there’s increase in cortisol, epinephrine, and norepinephrine (46).

Hypohydration stimulates the catabolic hormones by increasing core temperature (69,70) and increases cardiovascular demand due to decreased plasma volume (71,72,73). A 3% to 4% loss of body weight (water) reduces strength by about 2% and power by about 3% (35).

As noted before, a decrease in cell volume caused by hypohydration promotes insulin resistance (47,48,49). Resistance exercise might exacerbate the effects of hypohydration on insulin resistance, because muscle damage is also related with insulin resistance (74,75,76,77). There’s decreased GLUT-4 protein content (78,79), and impaired insulin signal transduction at the level of IRS-1, PI 3-kinase, and Akt-kinase (75). Downhill treadmill running and resistance exercise result in transient insulin resistance (80,81,82), and the reductions in glucose uptake in muscle damage models may be of the order of 20–30% (78,80).Muscle damage and insulin resistance










Hyponatremia – Extreme exercise conditions (equal or above three hours continuously), such as the marathon or triathlon, without the intake of electrolytes increase the risk dehydration or hyponatremia (83). Symptomatic hyponatremia is typically observed with greater than 6 hours of prolonged exercise. Acute water toxicity happens due to rapid consumption of large quantities of water that greatly exceeded the kidney’s maximal excretion rate (from 0.7 to 1.0 L/hour) (1).

Severe exercise-associated hyponatremia (EAH) starts as significant mental status changes resulting from cerebral edema, at times associated with noncardiogenic pulmonary edema (84,85). The osmotic imbalance results in fluid movement into the brain, causes swelling, which then leads to disorientation, confusion, general weakness, grand mal seizures, coma, and possibly death (35,124,125,126).

Exercise-associated hyponatremia (EAH) typically occurs during or up to 24 hours after prolonged physical activity, and is defined by a serum or plasma sodium concentration below the normal reference range of 135 mEq/L (86,87).

Usually only less than 1% of marathons athletes present signs of EAH (88,89), however it was as high as 23% in an Ironman Triathlon (90) and 38% in runners participating in a marathon and ultramarathon in Asia (91). There’s also now a trend for symptomatic EAH for shorter distance events, such as a half marathon (92) and sprint triathlon taking approximately 90 minutes to complete (93). There’s also no statistical significance for the incidence of symptomatic between genders (55), though women may be at greater risk than men (55).

We have seen that the major risk factor for developing EAH is excessive water intake beyond the capacity for renal water excretion (1,100,101) largely as a result of persistent secretion of arginine vasopressin (102,103). Elevations in brain natriuretic peptide (NT-BNP) may lead to excessive losses of urine sodium and raise the risk of hyponatremia (104).

Another concern is the inability to mobilize body sodium bound in bone. Sodium can be released from internal stores such as bone (105,106,107), 25% of body sodium is bound in bone (osmotically inactive) and is potentially recruitable. Inability to recruit sodium from that pool may increase the risk of hyponatremia.

Individuals under normal conditions are able to excrete between 500 and 1000 mL/h of water (108), plus the non-renal losses of water as sweat, so athletes should be able to consume as much as 1000 to 1500 ml/h before developing water retention and dilutional hyponatremia, therefore it seems likely that excessive water intake (>1500 mL/h) is the main cause.

The combination of excessive water intake and inappropriate AVP secretion will clearly lead to hyponatremia.exercise associated hyponatremia pathogenesis






Arginine vasopressin (AVP) must be suppressed appropriately with water loading, otherwise the ability to produce dilute urine is markedly impaired (109).

Water can also be absorbed from the gastrointestinal tract at the end of a race causing an acute drop in serum sodium concentration (110), with clinical signs of EAHE after 30 minutes. During exercise, breakdown of glycogen into lactate increases cellular osmolality and rises serum sodium, but some minutes after exercise this is reversed and serum sodium levels drop (111,112).

The risk also rises if the degree of fluid loss through sweat is sufficient to produce significant volume depletion (stimulating AVP release and impairing urine excretion of water), coupled with ingestion of hypotonic fluids (86).

Although not conclusive, nonsteroidal anti-inflammatory drugs (NSAIDs) have been implicated as a risk factor in the development of EAH by potentiating the water retention effects of AVP at the kidney (86).

At least two strategies can be used to present EAH: avoid overdrinking (real time sensation of thirst) and limiting the availability of fluids during events. Supplementation with sodium may delay of even prevent the decline in blood sodium concentration (113,114) however drinking beyond thirst (overdrinking) will not prevent hyponatremia (115), the amount of fluid ingested is more important than the amount of sodium ingested for blood sodium concentrations (116).

EAH has a complex pathogenesis and multifactorial etiology:exercise associated hyponatremia field management (1)







An athlete should consume approximately 500 to 600 mL (17 to 20 fl oz) of water 2 to 3 hours before exercise (117). By hydrating several hours prior to the exercise, there is sufficient time for urine output to return toward normal before starting the event (30).

For normal athletic events in moderate temperatures (and altitudes), it should be enough to hydrate slowly over several hours. If the body needs water urgently it can absorb some water right through the walls of the stomach. A 1% to 2% decrease in your body weight (due to water loss) will affect performance.

The threshold for reduced performance appears to be 2% body water loss of total body mass (118,119). Dehydration equivalent to 1.5% to 2% of total body mass may decrease performance up to 15% (120). We’ve seen before that 3% to 4% losses impairs muscular strength by 2% and muscular power by 3% (35), and also reduces high-intensity endurance performance (e.g., distance running) by approximately 10% (123).

Energy drinks

Energy drinks typically contain water, carbohydrates, vitamins, minerals, with the aim of increasing energy, alertness, metabolism, and/or performance (e.g., caffeine, taurine, amino acids, glucoronolactone…) (127).

Caffeine is the most common ingredient, and is absorbed in 30 – 60 minutes (128). Caffeine original_238495_hro087gobfL4M69kTZcwERglvstimulates the cardiovascular system and increases epinephrine output (129,130); enhance vigilance during bouts of exhaustive exercise, and periods of sustained sleep deprivation. Energy drinks with approximately 2 mg·kgBM-1caffeine consumed 10 to 60 minutes prior to anaerobic/resistance exercise may improve upper- and lower- body total lifting volume, and improve cycling and running performance (127).

Carbohydrate feeding during exercise can improve endurance capacity and performance (131,132), through maintenance of blood glucose levels, high levels of carbohydrate oxidation (1 g of carbohydrate per minute), while sparing liver and skeletal muscle glycogen (133).

Energy drinks also have a small amount of vitamins (e.g., Vitamin B6, Vitamin B12, pantothenic acid, Vitamin C) and electrolytes (e.g., sodium, potassium, phosphorus, etc.).

Energy drinks can improve mood, reaction time, and/or markers of alertness, most likely due to the ergogenic value of caffeine and/or carbohydrate.

Caffeine can elevate metabolic rate and the rate of lipolysis. 200-500 mg of caffeine (typical of thermogenic supplements) can increase acute energy expenditure (1-24 hours) (127), chronic energy expenditure (28 days) (134), and elevate plasma free-fatty acid, glycerol levels and catecholamine secretion (127, 134). The caffeine in energy drinks ranges from 80-200 mg, and it’s not conclusive whether daily use of ED would affect long-term energy balance and body composition (127).

Individuals with metabolic syndrome and or diabetes mellitus should avoid consumption of high glycemic drinks and/or foods. More importantly, individuals with known cardiovascular disease should avoid any use of energy drinks due to the cardio stimulant effects (124).

More references here than there are chopsticks in a Chinese restaurant

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Interview with Stacy Sims PhD CISSN

SNI:  From the standpoint of rehydration, is there an ideal percentage of carbohydrate that is needed when consuming fluids?  Is there a combination of carbohydrates that is ideal?HE_sports-drinks_s4x3_lead
Stacy: In my experience working with athletes, they are so focused on calories that they don’t pay attention to the fact that what they are drinking contributes to FUELING, not HYDRATION.

Let me explain.

In science speak: During prolonged exercise, fluid and salt losses through sweating reduce plasma volume which leads to heart rate drift in association with hyperthermia and reductions in performance. Oral rehydration with water reduces the loss of plasma volume and lessens heart rate drift and hyperthermia. Moreover, the inclusion of sodium in the rehydration solution to levels that double those in sweat (i.e., around 90 mmol/l Na+) restores plasma volume when ingested during exercise, and expands plasma volume if ingested pre-exercise.

In real person speak: During exercise you lose water and salt through sweat. When you lose this water and salt, the watery part of your blood also drops. With less water in your blood, the blood is more viscous, thus you end up with a higher heart rate, lower power production, and a greater rise in core temperature->all leading to fatigue, reduced performance, and the dreaded power decline when it counts the most: at the end of a race.

There is a competition within the body when you start to exercise: Your muscles and your skin fight for your blood. Blood goes to the muscles for metabolic function. Blood goes to the skin to get rid of the heat produced by the working muscles. As body water drops, this competition becomes more fierce, and the skin blood flow will win out- Primarily because heat is a greater threat to the body than keeping the muscles working (which produces heat..).

The fatigue you experience is that drop in blood flow to the muscle- basically you have less metabolism functioning plus protein denaturing (the contractile proteins denature, aka stop working, in muscle temperatures >~39’C).

“Ok” you say, “But I’m drinking so I should be able to circumvent this blood volume problem.”

BUT here is where things go south. It’s what you’re drinking that’s making you dehydrated.

The mass market out there has the message that when you drink a 4-8% carbohydrate solution with sodium (~220mg sodium per liter) you are taking care of your hydration and fueling needs. The focus is always on carbohydrate availability and calories. (If you do a literature search on  hydration and carbohydrate for endurance exercise you will find the hydration research is really carbohydrate availability in the form of liquid calories.)

I’m here to tell you, as a physiologist that specializes in hydration, thermoregulation, and performance; this is a misleading and incorrect message.

Let’s look at two key factors needed to pull fluid into the body’s fluid spaces:
1) You need what you are drinking to have an osmolality below that of blood. (osmolality is the amount of solutes in a solution. The more active solutes in a fluid, the higher the osmolality. Blood sits ~285mOsm)
2) You want what you are drinking to meet the physiological needs of fluid absorption- this means that you want your fluid to have fluid co-transporters: the intestinal cell membranes use sucrose, glucose, and sodium (Na+) as facilitators to get fluid across the cells into the water spaces of the body.

Now let’s look at the nutritional aspects of a typical sports drink:
– 5-6% carbohydrate solution
– Osmolality of ~300-320mOsm
– Sugars: maltodextrin, fructose, sucrose
– Sodium: ~220mg per liter

With the higher osmolality than blood, the physiological response is to pull water from within the vascular spaces of the body to “dilute” higher osmolality. This creates a net gradient of water leaving the body into the digestive system. Problem: effective dehydration and GI distress.

The 5-6% solution provides exogenous carbohydrate but not in the levels needed to sustain longer term endurance exercise without energy fluctuations (you want 4-6 calories per pound of body weight of mixed macronutrient food- different rates of oxidation/breakdown means a greater time and titration of fuel to the body)

The maltodextrin and fructose are notorious for causing GI distress; free fructose (e.g. not from sucrose) has to go through the hepatic portal vein to the liver to be processed, and no rate limiting effect for this free fructose  will cause a “dumping” of fructose into the system,  leading to major GI distress. Maltodextrin exits the stomach quickly, but in the intestines, pulls water into the digestive tract =  GI distress (aka diarrhea!)

Sodium and sucrose- these are the only two potential “helpers” in fluid absorption, BUT by the nature of the osmolality of the 5-6% solution, the net gradient of fluid is to come from within the body into the gut, thus the sodium and sucrose work with this gradient to facilitate fluid movement through the intestinal cell membranes into the GI tract.

SNI: Should protein be in a rehydration drink? Yes, No, Maybe so?

Stacy: Post exercise is a key window for several things; primarily being maximum effect on muscle synthesis and glycogen recovery. The “critical” window for high quality protein intake is the 30 min post exercise; this is also part of the critical rehydration window- start rehydrating to decrease the negative effects on the immune system. I’m bending towards the question in a roundabout way to say Yes, protein is beneficial for rehydration just as it is essential for muscle reparation and synthesis. A small inclusion of protein in a low carbohydrate-concentration rehydration drink does facilitate plasma volume expansion, increases absorption of electrolytes and boosts levels of plasma proteins, which promote long term hydration after exercise. Keep in mind, however, rehydration post-exercise is different from rehydration from a long day at work, not drinking. The protein promotes muscle reparation, but also adds calories. Being cognate in the timing of your nutrients becomes critical for recovery and body composition changes.

SNI: What are your thoughts on caffeine?  It is commonly held that caffeine is a dehydrating agent.  What’s the science say?

Stacy: Ah, “Black Gold”… Caffeine is a great addition to any endurance athlete’s arsenal for performance. There are three ways caffeine may provide ergogenic effects. First, the central nervous system is directly stimulated by caffeine (blocking receptors for adenosine and increasing plasma catecholamines), which helps reduce the sensation of fatigue, increases alertness, and increases muscle recruitment. Second, caffeine has been shown to improve endurance through the increased utilization of fat as a fuel and sparing carbohydrate utilization (a.k.a glycogen sparing effect); and most recently, it has been demonstrated that caffeine increases the calcium content of skeletal muscle, thus enhancing the strength of muscle contraction. Caffeine & Hydration –  Staying hydrated, while important for humans at all levels of activity, is especially important for athletes during vigorous exercise. Historically, athletes have been advised against consuming caffeine because of caffeine’s mild diuretic effect.  However, a point often missed is that any fluid, caffeine-coffee-beansincluding water, will also have a mild diuretic effect. In a review of hydration and caffeinated beverages, Lawrence Armstrong, PhD concluded that “it is unlikely that athletes and recreational enthusiasts will incur detrimental fluid-electrolyte imbalances if they consume caffeinated beverages in moderation and eat a well-balanced diet.” Contrary to popular belief, research has shown that caffeinated beverages can and do contribute to hydration.


SNI: For the endurance athlete who just ran, cycled or swam for 2 hours, what would YOU suggest they consume immediately post workout to promote fluid balance, glycogen repletion and skeletal muscle recovery? Do you have a ‘Stacy Sims recovery’ cocktail?

Stacy: There are two options here, one is nonfat greek yogurt with manuka honey within 30 min post exercise to address the nutritional needs of the muscle (yogurt is great for whey and casein, potassium, sodium, calcium, magnesium; manuka honey provides a bit of extra carbohydrate with natural immune boosting properties), then over the course of 2 hours, slowly rehydrate with a 1.5% glucose-sucrose solution with 200mg potassium and 100mg sodium per 16oz at a rate of 0.15oz per pound of body weight per hour.  The second option (and my “go-to”) is OsmoNutrition’s Acute Recovery. It is an organic, high quality (no hormones, non-GMO) protein recovery drink. It is unique as well as it doesn’t have any antioxidants in it and it has a wee bit of green tea extract for caffeine. As much hype as there is around antioxidants, you really don’t want them close to the end of exercise as antioxidants impede mitochondrial adaptations to endurance exercise stress. And the wee bit of caffeine helps facilitate glycogen repletion ~66% over protein+carbohydrate alone. In addition to this drink (again within 30 min post exercise), I recommend the same dosage of the 1.5% solution per above. Trying to cover both nutritional needs of the body with rehydration needs requires the separation of food and fluid.. Post exercise the first point to cover is protein and carbohydrate; the second aspect to cover is total fluid recovery. The window for muscle recovery is much smaller than fluid recovery; thus pay attention to the acute recovery needs first to maximize the adaptations induced from the exercise stress.
SNI: What do YOU personally consume pre, during and post-workout?

Stacy: Ah! I’m not training much right now as work and my new daughter take most of my time; but when I do head out, I usually have the pre covered by my most recent meal, during I use Osmo Active hydration with real food (I tend to like homemade protein bites or power cookies…) and post exercise, Osmo Acute recovery. 

SNI: What athlete do you admire the most and why?

Stacy: There are so many great role models and inspirational women out there, including some of my own clients; but I’m going to pull a name out of the past: Gabrielle Reece. She was my role model when I first discovered competitive sport and I still admire her for everything she has accomplished. Not only is she a world class athlete, she is a strong role model for athletic, career driven moms- not a super woman, but close enough!

BIO: Dr. Stacy Sims, MSc, PhD

Exercise Physiologist-Nutrition Scientist, CISSN
CRO-Research Scientist
Osmo Nutrition

Stacy served as an exercise physiologist and nutrition scientist at Stanford University from 2007-2012 where she worked as an environmental exercise physiologist and nutrition scientist specializing in recovery, and nutritional adaptations for health, body composition, and maximizing performance. During the past decade Stacy has worked as an environmental physiologist and nutrition specialist for top professional cyclists, ultraswimmer Jamie Patrick, the Garmin/Slipstream Pro Cycling Team, USA Cycling Olympic Team (BMX and women’s track cycling), Team Tibco, Flying Lizard Motorsports, and Team Leopard-Trek, among others. Stacy earned a BA from Purdue University, an MSc from Springfield College, a doctorate from University of Otago, and was a postdoctoral research fellow in cardiovascular disease prevention, thermoregulation, and women’s health at Stanford University. Stacy raced crew as an undergraduate at Purdue University, raced Ironman at an elite level in the early 2000s but now competes as a Cat 1 road cyclist and an elite XTerra triathlete.