What you can do to manage your hydration on race day — Nuances, practicalities, and logistics.
Thomas Solomon PhD.
12th September 2021.
If you want to understand the physiology of water and electrolyte balance and examine what we know about hydration, then check out Part 1 of this series. If you want to know why there is contradiction in the narratives about hydration, then check out what we aren’t sure about in Part 2. If you want to fully understand why there is confusion about sodium (salt), then check out what we don’t know about in Part 3. But, if you don’t care about any of that, you are in the right place because today in the fourth and final part of this series I will delve into the nuances, practicalities, and logistics of what you can do to manage your hydration on race day.
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On this watery journey, my intention was to keep you “afloat” and stop you “drowning” by untangling the hydration confusion. Knowing how much to drink during exercise is a sentiment exploited by many companies trying to market their “hydration” products. Lots of info; so little clarity. Even when given the same race-day drinking advice and equal access to fluid, runners respond individually and variably. The “fear” of being dehydrated during exercise and some folks’ subsequent drive to drink as much as possible must be driven by misinformation. In sports drinks marketing campaigns and on the media/social media channels that promote them, you have probably read statements like:
“Exercise performance is significantly impaired when 2% body weight is lost during exercise.” “To stay hydrated during exercise, you need to drink to replace sweat losses.” “Drinking to thirst does not work because the feeling of thirst comes too late.” “To perform at your best, you must replace electrolytes during exercise.”
Well, if you have sipped on the knowledge from Part 1, Part 2, and Part 3, of this series you will understand why hydration is such a confusing topic but you will also now be very well versed in the evidence telling us that all these sentiments are rather off-piste.
Why? Well, to summarise...
Because, while starting exercise hypohydrated will likely manifest a performance detonation, you’ll likely be totally fine if you start exercise euhydrated.
Because larger weight loss during exercise is not correlated with poorer performance and because weight loss during exercise does not necessarily indicate that total body water has decreased.
Because under “normal” ambient conditions (<25°C), a 2% weight loss during exercise has negligible effects on performance and most people can tolerate up to 3-4% (some as much as 9%!) weight loss before performance declines. Weight loss during exercise (as a biomarker for dehydration) is only associated with impaired endurance performance in hot conditions — i.e. dehydration typically only impairs performance when your need to cool down is imperative.
Because when drinking to replace all sweat losses during exercise (aka planned “drinking to a schedule”) you might hyperhydrate and cause hyponatremia.
Because thirst is our only “biomarker” indicating that we need to drink, and “drinking to thirst” (or ad libitum drinking) can maintain hydration status, even during ultra-distance races in the heat (i.e. above ~25°C). And,
Because sodium supplementation (and/or sodium preloading) is generally unnecessary for maintaining plasma sodium concentrations and performance and likely only becomes “necessary” during very long duration races if you have a high sweat rate with a high sweat sodium concentration.
With hydration, there are knowns (Part 1)... there is debate about uncertainties (Part 2)... and, there are unknowns (Part 3). The synthesis of evidence starts with anecdotes, then observational studies and randomised controlled trials (RCTs). When there are enough RCTs, a systematic review can collate the experimental evidence and a meta-analysis can tell us the overall effect size. The experimental evidence derived from this scientific method can then be combined with empirical evidence from ecologically valid “in-the-field” observations to synthesise guidelines. So, surely clinical guidelines have a clear answer. So...
Let’s take a look at the sports nutrition hydration guidelines.
Warning: a historical dive into the pool of hydration guidelines can be confusing...
In 1996, the ACSM position stand stated that “athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating (i.e., body weight loss), or consume the maximal amount that can be tolerated”. In 2007, ACSM updated their position, stating that “The goal of drinking during exercise is to prevent excessive dehydration (>2% bodyweight loss from water deficit) and excessive changes in electrolyte balance to avert compromised exercise performance. The amount and rate of fluid replacement depends upon the individual sweating rate, exercise duration, and opportunities to drink.” and that: “A possible starting point suggested for marathon runners (who are euhydrated at the start) is they drink ad libitum from 0.4 to 0.8 litres per hour, with the higher rates for faster, heavier individuals competing in warm environments and the lower rates for the slower, lighter persons competing in cooler environments.”. In 2016, ACSM’s update read... “The fluid plan that suits most athletes and athletic events will typically achieve an intake of 0.4 to 0.8 Liters per hour, although this needs to be customized to the athlete’s tolerance and experience, their opportunities for drinking fluids and the benefits of consuming other nutrients (eg, carbohydrate) in drink form.” And, that “Sodium should be ingested during exercise when large sweat sodium losses occur. Scenarios include athletes with high sweat rates (>1.2 Liters per hour), “salty sweat,” or prolonged exercise exceeding 2 hours in duration. ”.
If you followed my series on hydration, you will notice how these updates converge on what we know and what we don’t know (or aren’t sure about). But, positions from other governing bodies and societies keep things interesting… For example, the 2019 IAAF Consensus Statement on Nutrition for Athletics said to “Aim to keep net fluid deficit <2–3% body mass, especially in hot weather.” while the 2018 ISSN exercise & sports nutrition position stand advised that “to maintain fluid balance and prevent dehydration, athletes need to plan on ingesting 0.5 to 2 Liters per hour of fluid to offset weight loss.”. But, a year later, the ISSN further confused things in their 2019 position stand, recommending that “day-to-day hydration can, in most instances, be achieved by following a drink-to-thirst (ad libitum) strategy.” but “to inform post-training rehydration strategies, athletes should measure pre- to post-exercise body mass losses, and monitor their hydration status.”.
Phew.
So, if you choose to use societal guidelines/position stands to inform your hydration choices, only use up-to-date guidelines but stay mindful that even the most recent guidelines can include conflicting and, therefore, confusing recommendations.
Although dehydration-related health risks during exercise are rare (see Part 1), it is prudent to be a healthy athlete. Since overzealous hydration can easily harm your health, I typically prioritise hydration guidelines that minimise the risk of exercise-associated hyponatremia. The 2015 Position Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference stated that: “Under-replaced sodium losses contribute to serum sodium concentrations independent of distance. However, there is paucity of data supporting sodium loss as the primary mechanism of symptomatic exercise-associated hyponatremia even in those who exercise for prolonged periods of time and in warm weather.” and “Given that excessive fluid consumption is a primary etiological factor in exercise-associated hyponatremia, using the innate thirst mechanism to guide fluid consumption is a strategy that should limit drinking in excess and reduce the risk of developing hyponatremia while providing sufficient fluid to prevent excessive dehydration.” Nice.
Earlier, I said that clinical guidelines are synthesised from systematic reviews of experimental evidence combined with empirical observations. Unfortunately, current hydration guidelines and positions largely ignore existing systematic reviews. This is regrettable because the whole point of systematic reviews and meta-analyses is to reduce bias in errors of judgement and no human is immune to errors of judgement, not even “expert” authors of guidelines/position stands. For this reason, clinical guidelines for staying hydrated during exercise from the various bodies are puzzling and don't provide the clarity you deserve. Accordingly (and unsurprisingly), athletes’ knowledge and beliefs about hydration are also rather convoluted as shown by large surveys of endurance athletes and athletes surveyed at world major marathons.
So, what now…?
To help settle debates and resolve confusions, it is often best to take an empirical approach and see what real people actually do. So...
How do athletes “hydrate” on race day?
During the marathons of old, folks drank very little, sometimes nothing. Through the 1950s, competitors in marathons were not permitted to carry or take refreshments other than that provided by the race. This held true until an IAAF (now World Athletics) rule change in the 1960s, which allowed runners to drink every 5 km after the 11 km mark. Nowadays, water is everywhere — every marathon has a drinks table every 5 km.
But how much do we drink?
During the Tokyo 20201 Olympics’ marathons, which were run in ~28°C heat and ~70% humidity (see women and men here), folks at the front (the ones on camera) drank very little at each aid station. I noted that Kipchoge took ~1 quick sip (~50-100 mL) from a bottle every 5 km (~15-mins) — possibly 200 to 400 millilitres/hour (mL/h). But, this is an anecdote from my eyes only and I only saw what the camera showed me. So, what about objective observations?
The classic “desert” studies from Adolph in the 1940s showed that folks almost always drink less than they sweat during exercise and consequently develop “voluntary dehydration” without detrimental consequences, and then naturally remedy the dehydration during post-exercise meals. This perhaps sounds very familiar — you probably feel a little thirsty at the end of almost every session and you “treat” that by simply drinking fluid and eating food afterwards and all is well.
But, how much do trained runners drink during races?
During half-marathons, runners “drinking to thirst” have reported consuming 384±180 mL/h and 326±180 mL/h in cool to moderately warm conditions. During ultra races, runners have reported drinking 378±164 mL/h and 538±354 mL/h in cool to moderately warm conditions. In the heat, fluid intakes increase. During a 225 km ultra-marathon in 32-40°C heat, athletes drank 732±183 mL/h while folks at the 24-h World Champs drank 685±290 mL/h. And, a massive study of 3317 ultrarunners competing distances of 65 to 165 km in hot and humid conditions found an intake of 663±240 mL/h. These observations show that:
Under cool to warm conditions (<25°C), the average runner drinks ~380 mL/h.
Under hot conditions (≥25°C), the average runner drinks ~700 mL/h.
But, what about elite world-class athletes (aka above-average runners)?
Studies of world-class Kenyans’ ad libitum food and fluid intake shows a daily fluid intake of 3.8±0.8 L/day, a daily sodium intake (~3.2 g/d) that matches daily sodium losses, and daily maintenance of hydration status. At various Olympics and world majors marathons, observations showed that athletes drank 550±340 mL/had libitum. Furthermore, none of the marathoners “drank to a schedule” to replace sweat losses and all of them broke 2:10, including the winner (Haile Gebrselassie) of the 2009 Dubai marathon who finished in 2:04 with a 5.7 kg (or 9.8%!!) loss of body weight. Additionally, a study of elite marathoners and race-walkers at the 2019 World Championships showed that most athletes (93% or 77/83) had a pre-planned hydration strategy but that personal experience was the major determinant for their strategies (91%, or 75/83), outweighing information from a coach, nutritionist, scientist, further reading, or expected fluid availability. Furthermore, neither the type of hydration strategy or the extent of during-race dehydration was associated with athletes’ race performance or finish position. So...
What do we learn from what real athletes do on race day?
It is clear that athletes drink fluid and eat food during races and that some athletes take sodium (the necessity for which is unclear and, under most circumstances, is probably unnecessary; see Part 3 for details). But, athletes don’t drink to replace sweat losses and the average “drink to thirst” (or ad libitum) fluid intake during a race is ~500 mL/h, in the ballpark of the most recent ACSM guideline of 0.4 to 0.8 L/hour. Athletes also drink less than they sweat and finish races in a state of “voluntary dehydration” (without any ill-health) which they then remedy after exercise with meals and drinks. In fact, replacing bodyweight losses with fluid does not enhance performance (see Part 1 and Part 2 for details), faster performances are made by those who lose more weight. But, THIS IS NOT EVIDENCE that you should strive for the largest weight loss possible during a race because we do not understand why some folks can “tolerate” such great weight loss during exercise.
So, our observational binoculars show that “drinking to thirst” does a pretty good job of maintaining hydration status and performance. We also know that “drinking to thirst” prevents hyperhydration and thereby minimises the risk of hyponatremia. But, managing hydration is clearly an issue for some athletes (see Part 1 and Part 3) and, as I discussed in Part 3, sodium losses during exercise can cause hyponatremia independent of plasma sodium being “diluted” by drinking too much fluid. So, now we arrive at the most important question of all…
How can you manage your hydration on race day?
The first thing I advise is to learn to stay safe and healthy with your hydration strategy. So...
Learn to recognise the signs and symptoms of drinking too much and drinking too little.
The consequence of hypohydration is ongoing dehydration (water leaving the body) that triggers a feeling of thirst, which, if not remedied in the short-term (by drinking fluid), can lead to a bunch of signs and symptoms of mild dehydration:
ongoing thirst, a dry/sticky mouth, headache, dizziness, cramps, excessive fatigue, irritability, low motivation, loss of speed, loss of skill, and even a small weight loss.
(you don’t need all these things to be present and there are other causes of some of them)
Don’t ignore these things, some fluid might be all you (or your athlete or child) need, and ignoring them in hot conditions will increase your (or your athlete’s or child’s) risk of heat-related illness (more on that in an upcoming post). Completely ignoring these signs and symptoms could cause you (or your athlete or child) to become confused or even lose consciousness, in which case seek medical attention. In the long-term, chronic dehydration can kill.
Naturally, some folks are overzealous with hydration and drink too much. This is interesting because Hyperhydration is not triggered by thirst, our biological cue to drink what we need. But, during normal daily tasks, in healthy folks, hyperhydration simply leads to peeing more. No major drama. But during “unusual” conditions — e.g. prolonged exercise, particularly in hot conditions when you might be losing more sodium than usual — hyperhydration can further “dilute” your decreasing plasma sodium concentrations. In this context, the major consequence of hyperhydration is exercise-associated hyponatremia (plasma sodium <135 mmol/L). The signs and symptoms of mild symptomatic exercise-associated hyponatremia include:
dizziness, lightheadedness, nausea, puffiness, and weight gain.
(some of these are similar signs and symptoms as for other conditions including exertional heat illness, acute mountain sickness, hypernatremia, etc; hence the need for clinical judgement)
Severe exercise-associated hyponatremia presents with vomiting, headache, and behavioural changes like confusion, agitation, disorientation. Worst case: you can die. So, never ignore these signs and symptoms.
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This sounds dramatic but the incidence of health-related complications from dehydration or hyponatremia during exercise is extremely low. No doubt you have experienced some of these signs; hopefully, they were transient and disappeared after stopping and eating and drinking. No. Big. Deal. But being aware of them may one day help you or someone else. Being aware of the potential consequences will also help you understand why there is a precipitous debate surrounding appropriate hydration strategies.
Right, managing your health is in the bag... what about the thing you really care about: your race day performance? So...
How can you drink like a legend?
Don’t worry, my performance hydration framework has not been shaped by multi-night benders at university but it is simple and it goes like this:
Learn. Plan. Practice.
Learn to stay hydrated day-to-day.
As discussed in Part 1 and Part 2, starting your sessions/races adequately hydrated will get you most of the way there. In doing so, always remember that you cannot “adapt” to dehydration. Training helps your body adapt to be better at cooling during exercise but deliberately training in a dehydrated state will simply bury you in a hole, possibly literally.
Since our thirst mechanism evolved with us over millions of years, your hypothalamus likely knows better than any company trying to plug their latest “hydration” product. And, based on what we know about human physiology and the tightly-regulated neuroendocrine control of hydration, if you are healthy, to help maintain hydration on a daily basis, it is very likely that drinking to thirst will appropriately respond to your daily needs. So, carry a bottle of water with you so you can sip fluid to quench your thirst, including the days prior to your race and on the morning of the race. Furthermore, if you have access to food and fluid between your sessions and races, your body water and electrolyte levels will very likely be appropriately maintained every 24 hours.
If you are concerned that your daily hydration needs are not being met, consider using the Weight Urine Thirst (WUT) tool, which I discussed in Part 1. Every morning ask yourself 3 simple questions:
Is my morning body Weight more than 1% lower than yesterday morning? (Note that up to a 1% variation in daily body weight is normal — e.g. up to 0.6 kg if you weigh 60 kg.)
Is my morning Urine dark?
Am I Thirsty?
If you answer “Yes” to any 2 of the questions, your daily fluid intake is likely inadequate and you probably should have drunk more fluid yesterday… If you answer “Yes” to all 3 questions, your daily fluid intake is very likely inadequate and you should have drunk more fluid yesterday. But, don’t lose your mind over this… It is a guide, not a rule. If you think you might need to drink a little more fluid, drink some. If you think you have a “drinking problem”, see your doctor.
(If necessary) Learn to use a strategy to stay hydrated during your sessions/races.
Why do I say, “if necessary”?
Well, during this series, you learned that:
Larger body mass = larger energy expenditure = more heat = higher sweat rate.
Faster speed = larger energy expenditure = more heat = higher sweat rate.
Longer duration = you will sweat for longer.
Higher ambient temperature = greater need for cooling = higher sweat rate.
Higher sweat rate = higher sweat sodium concentration = greater potential for sodium loss.
Yep, it is complex but you don’t need to fret over water and sodium intake during every session/race. So, stay calm…
If your session/race is short — less than ~1-hour — it is highly unlikely that you will need to drink anything at all, let alone need to “get your electrolytes in”. But, if you do become thirsty and want to drink, then drink to quench your thirst. During a longer session/race — more than ~1-hour — “drinking to thirst” will very likely meet your hydration needs while also keeping you safe (from hyponatremia) and keeping your performance rocking. Yes, the feeling of thirst comes after dehydration has occurred (after water has left the “tank”) but thirst does not indicate that it is too late to drink fluid nor does thirst mean your performance is declining. So...
If you feel thirsty, drink some fluid to quench your thirst.
If you crave something salty, eat something salty.
It’s not rocket science… It’s evolutionary science. This is what your ancestors did to pass their genes onto you and a “craving” for water or salt is your neuroendocrine system telling you that your plasma volume and/or plasma osmolality need restoring — your tank needs topping up.
During long-duration moderate to high-intensity exercise, either “drinking to thirst” (or ab libitum) or planned mL/h “drinking to a schedule” can improve performance compared to no fluid intake. But, of course, there are nuances....
Don’t consider “drinking to thirst” and “drinking to a schedule” as opposite sides of a debate but rather as two separate tools for your hydration toolbox.“Drinking to thirst” will never make you hyperhydrate — it is safe — but your choice to use an alternative strategy might be shaped by your personal preferences and the logistics on the day. So, it is important to be mindful of your feeling of thirst and responding to it but it is also wise to have some idea of your fluid needs.
Whatever you do, always remember that if your fluid intake strategy makes you gain weight during exercise, you are hyperhydrating and increasing your risk of hyponatremia (plasma sodium <135 mmol/L), which can be fatal.
To help estimate your fluid needs, you can use your bodyweight change during exercise to estimate your sweat rate (see Part 2 and example here). You could also opt for one of the consumer sweat patch devices (e.g. Gatorade) that are emerging to market. Note: I am not affiliated with, sponsored by, or receiving royalties from Gatorade but their sweat patch technology has been well-validated. But, when estimating your sweat rates, increased accuracy will come from repeatedly determining your sweat rate at different exercise intensities, outdoors, under different climatic conditions. And, always remember that sweat rates and weight loss during exercise only provide a rough estimate of the change in total body water and your fluid intake should never aim to replace all sweat losses.
If you are concerned that you have very salty sweat, you could opt for a sweat sodium test (Precision Hydration) or you could try a sweat patch (Gatorade). Note: I am not affiliated with, sponsored by, or receiving royalties from either company but their sweat sodium tech has been well-validated. But, there is currently no experimental study that has examined the performance or health effects of quantified sodium replacement according to an athlete’s expected losses.
Sodium supplementation is generally unnecessary for maintaining plasma sodium concentrations and performance. Pre-exercise sodium loading might help reduce thermal stress and might delay fatigue when racing at a moderate intensity in the heat but the ergogenic effect of sodium supplementation on performance is not convincing. Sodium supplementation during exercise only likely becomes “necessary” during very long duration races if you have a high sweat rate with a high sweat sodium concentration.
If you choose to “get salty”, be aware that going beyond ~2.8 grams of sodium per litre (~120 mmol/L) pushes most folks into the unpalatable and/or gastrointestinal problem zone: Bonjour, gingerbreadman. Bonjour, veritable fountain of puke. Bonjour, DNF monster.
If you are sweating huge amounts of very salty sweat for long periods of time, remember the Gin & Tonic analogy from Part 3: When you pour a weak G&T into a strong G&T, despite adding more gin, you “dilute” the strong G&T and end up with less gin per litre of tonic. In other words, if you’re being a sweaty salty betty for a long time, drinking huge volumes of a “standard” sports drink (see Table 1 below) will lower your plasma sodium concentration. In that case, it is more prudent to increase the sodium concentration of your fluid (to a level that is still palatable) and/or to eat salty sodium-containing foods. (See Table 1 for a comparison between “standard” and “high sodium” drinks and energy gels.)
Since sodium intake before/during exercise is one of the biggest “unknowns” in the flood of hydration advice, no one can tell you exactly how much you need — it's up to you to try what works for you. If adding sodium to your during-race nutrition and hydration plan gives you peace of mind that you have “ticked that box”, then do it but know that it is probably unnecessary unless you are sweating a huge volume of very salty sweat, in which case you will likely need sodium at a higher concentration than that provided by “standard” sports drinks which is where “high” sodium drinks, energy gels, and real foods can be useful if you find them palatable.
Sodium-containing energy gels. NOTE: the high sodium concentration of most gels (combined with their high concentration of sugar) requires that they must be eaten with water to minimise GI problems.
Sodium in 1 gel (mg)
Sodium concentration in 1 gel (mmol/L)
Total sodium intake (mg) if you eat 3 gels per hour (~60 to 75 grams of carbs per hour)
Click here for calculations
The examples of “high sodium” sports drinks have sodium concentrations in the range of 45 to 150 mmol/L, providing between ~500 and ~1700 mg/h of sodium if you drink ~500 mL/h. Meanwhile, electrolyte-containing energy gels contain between ~60 and ~200 mg of sodium per gel and if you eat 3-gels per hour (to provide 60 to 75 grams of carbs per hour, adequate to maintain during-race high carbohydrate availability in most people) you will consume ~200 to ~600 mg sodium per hour — covering the sodium “needs” for the majority of people. Plus, the other foods you eat will likely contain sodium. Plus, the table salt (sodium chloride) you have at home contains ~400 mg of sodium per 1 gram (per 1000 mg) and can be added to your drinks.
Now that you have learned to stay hydrated day-to-day and during your sessions/races, you are now ready to...
Plan your race-day strategy.
“Drinking to thirst” vs. “drinking to a schedule” is not only a boring debate but is also reductionist because it neglects one key factor every racer knows:
When and where are your opportunities to drink during a race?
This changes for every race. Fluid is not always “on tap”, so having a rough idea of your hourly fluid needs during exercise can help you maintain hydration status during a race by drinking an “appropriate” volume when the opportunities arise. Therefore, you need a bespoke plan for each of your races that exploits the opportunities to drink fluid and eat food (carbs) throughout the race while addressing your feeling of thirst, minimising your feelings of hunger and gut discomfort, all the while maintaining a tolerable body water deficit and maintaining high carbohydrate availability. To do so, you will need to plan where you will drink fluid and/or refill bottles because it is useful to estimate how much fluid you’d like to carry between sources when fluid access is limited.
The logistics of stuffing fluid and food in your face during a road marathon is easy — there are feeding zones every 5 km — every 15-mins if you are Kipchoge, every 30-mins if you are a 4-hour racer — and, during road marathons, it is usually pretty easy to find out exactly what will be provided at each zone. But, in some events, like trail races and mountain races, there are very few feeding zones, perhaps one every 10 km — every 50 to 100-minutes or longer. And, in some obstacle course races, there are sometimes no feeding stations even in 3-hour races (?!). Consequently, it is a good idea to
Plan how you will carry fluid (and food).
During my own running career, I have experimented with backpacks, handhelds, belts, pockets, and even gaffer tape to get my water, energy drinks, gels, and food from A to B with minimal discomfort and maximal gain. Terrain, weather, comfort, practicality, and the duration and type of event have all played a role in my pre-event decisions, and Bayesian-like alterations to those decisions have been tweaked for subsequent events based on my experience during the event and the success vs. failure vs. “meh” outcome of my trial and error. But, one additional consideration that you might be pondering is...
Will carrying things affect your running economy and power-to-weight ratio?
Carrying 1 litre of fluid = 1 kg plus the weight of the thing the fluid is in. Earlier this year, I was due to race a 60 km ultra in the mountains of my “backyard”. When the actual race was cancelled due to pangolins and spike proteins, I ran the route self-supported, with a 3.2 kg pack containing all I needed (except for my rockstar wife providing water, beer, and banter at two strategic locations). Additional weight should increase the energy cost of running (using more of your body’s fuel stores) and increase RPE for a given speed, meaning that you need to slow down a little. Therefore, in such a scenario, one must consider how to carry things comfortably and efficiently; a balance between needs and avoiding excess baggage. But, there is a negligible effect of carrying light loads on running economy and no differences between hand-helds, belts, or packs (see here and here). So, your decisions regarding the logistics of planning your race-day hydration strategy can be based on personal choices.
As you will see on a world-class start line in a variety of races, there is no “one size fits all”. You will never see Eliud Kipchoge or Brigid Kosgei (WR holders in the marathon) wearing a waist belt or backpack with gels in their hands — they know they will visit their smorgasbord of treats every 15-minutes. You will also very rarely see Jim Walmsley or Kílian Jornet wearing a pack — they’re bottle carriers — and as sponsored and heavily-supported professional athletes they know their support crews will keep them on track. But, other sponsored and supported athletes like Jon Albon, Courtney Dauwalter, and Beth Pascall will often be seen wearing a pack during long events. You are the only you. And, all these long-duration mountain goats are constantly refining their approach, which brings me to my final point...
Practice your race-day strategy.
It should go without saying but this is something I see folks neglecting... Whatever you plan to do, don’t recce it for the first time on your “A” race day!
Be aware of what filling your belly with fluid just before gun time and/or during a race feels like. Running does to your stomach what an eddy current does to a white-water raft — eff dup mayhem. The mechanical bouncing and sloshing of fluid and food in your stomach is not only an odd sensation but it can also make you feel terrible or, worse case, turn you into a veritable fountain of puke. Don’t wait until race day to find this out. Similarly, it is not the stuff of dreams to discover on race day that your fancy new high-sodium “super-hydrating” Energyzade tastes like the back end of a dodgy rhino. It is always best to taste the rhino in training and learn that, “nope, this is too salty for me”.
During ultra-distance races, you will likely build a menu containing a variety of things you like to eat to keep yourself fueled, hydrated, and sane. This might include drinks, gels, bars, and real food (sandwiches, fruit, nuts, pretzels, soups, and “cream coloured ponies and crisp apple strudel. These are a few of my favourite things.”). All these things contain water, calories, sodium, and more. So, when the hills are alive with the sound of... your rumbling stomach, it’s a good idea to know what the items on your menu taste like when you’re deep into the pain cave.
During a long race, another priority besides hydration is maintaining a high carbohydrate availability to your hungry muscles (help the liver, save the brain, feed the muscles — hear all about that at veohtu.com/RacedayCarbAvailability). Fluid volumes, rates of intake, and grams of sodium and carbohydrate, all get a bit complicated. Time spent working out whether you can tolerate liquids or solids and their flavours and textures (etc etc) is time well invested.. So, write down what you think you’ll need to consume during your next race and recce how you might carry it and consume it during your next long run.
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Learn. Plan. Practice. Putting the framework together.
About 15-years ago, I repeatedly studied my sweat rate, sodium concentration, and osmolality at two different temperatures (20 and 30°C; humidity ~50%, wind speed ~4 kph) during 60-minute outdoor runs on the same route at two different intensities: easy pace (4:30/km, RPE 3-4/10; with no upward drift in heart rate or breathing rate) and marathon pace (3:45/km, RPE ~6/10). Having lived in my own skin for many moons, I already knew that my sweat rate would be high but I also knew that I did not suffer overtly when performing in the heat. At my marathon pace in 30°C, my sweat rate was 3.2 litres/hour, hence I lost ~3 kg body weight in my 60-minute run. At my easy pace at 20°C, my sweat rate was 1.1 L/h; pretty high considering this was a jog — I am a Sweaty Betty. To the “drink to a schedule to replace sweat losses” folks, these findings would suggest that my fluid intake should be at least 1.1 L/h during most sessions. But, I also learned that my plasma osmolality and plasma sodium were unchanged during easy and/or cool runs, and raised a little (but within the healthy reference range) during marathon pace and hot runs. I also learned that my sodium losses were not pronounced — I did not have particularly salty sweat (yes, I licked myself), as confirmed by my sweat sodium and osmolality measurements. Besides a feeling of thirst, I also had no other signs of dehydration or hyponatremia. My data suggest that in me, during events up to at least 60-mins, I need not have any fear of dehydration-related issues (health or performance) and that cramp (a sign of neuromuscular fatigue or electrolyte imbalance) and/or a loss of power output (fatigue) during long-hard efforts is highly unlikely to be caused by sodium loss.
Around the same time, going into my first road marathon, I also documented my food and fluid habits during my long sessions. I learned that my mouth could comfortably contain 98±10 mL of fluid and calculated that 3-mouthfuls of the drink provided every 5 km at the London marathon, Lucozade Sport Orange, would give me ~150 mg of sodium and ~20-grams of carbs every 18-mins (every 5 km) or ~450 mg/hour of sodium and 60 g/h of carbs. Using that plan, I discovered that having 300 mL of fluids sloshing around in one's belly every 18-minutes was horrible. But I also knew that my sweat rate (body fluid loss) at marathon pace in cool conditions (15 to 20°C) was ~1.5 litres per hour, so drinking ~900 mLs/hour would not place me at a higher risk of hyponatremia.
In prep for that marathon, I did many drink station workouts at the track to practice how to drink fluid while running at 3:45/km. A skill that is now imprinted in my neurons. In subsequent marathons, I ditched the fluid-only approach and successfully used an energy gel plus “drink to thirst” at water stations approach. And, ahead of those races, I invested time working out the best ways I could carry gels — belts, pockets, gloves, and even gaffer tape (which turned out to be the most effective and failsafe).
So... My old marathon days started with “science” and added the “art”.
Anyway, enough about me; this is about you. I intend my anecdotes to light your fire so you can douse it with your own hydration strategy. Now, you are ready to learn, plan, and practice your strategy.
What can you add to your hydration toolbox?
“Drinking to thirst” is a useful guide for daily living and a safe approach for managing hydration during exercise. However, during a session/race “drinking to thirst” is not possible when fluid is not available. Therefore, estimating your fluid needs can help you drink an appropriate volume when the opportunity arises. Similarly, eating an adequate amount of salt in your daily diet will likely address your during-exercise sodium losses. But, if you're an excessively heavy sweater with very salty sweat then consuming sodium as part of your during-race nutrition plan is probably sensible. That said, since sweat rates and sweat sodium losses are highly variable within and between different people, there is no single rate of fluid intake or rate of sodium consumption that can be recommended during exercise for all people. You probably don’t like that sentiment because it doesn’t tell you what to do. Most folks want information on a spoon. But, hydration is like The Matrix... there is no spoon. Hydration practices are underpinned by science but they’re also an art because of personal preferences and environmental conditions.
Some of you might “flush” everything you’ve heard in this series down the toilet to continue regulating your hydration as you have been doing: autonomically, without thought, just as your ancestors did to deliver you to your place on this globe… But, if you’re still confused and feel like you’re “drowning”, don’t let the simple act of drinking water become the most confusing aspect of your training… Instead, arm your training toolbox with a simple take-home taken straight out of your grandparents’ life rules:
“Listen to your body.”
If you feel thirsty, drink some fluid.
If you crave salt, eat something salty.
Never force yourself to drink large frequent volumes of fluid during exercise — this is rarely appropriate or healthy — slight hypohydration is safer than hyperhydration.
If you are showing signs of chronic dehydration or hyponatremia, don’t ignore them — stop and seek medical help.
During a race, plan when and where you will drink and/or carry or refill your bottles.
If it is hot and you're going long, adding sodium to your food/drinks might be necessary.
and
Always practice your race plan before race day.
Thanks for joining me on this deep-dive into the flood of hydration. I hope you were able to learn something by sipping from this glass of knowledge. Until next time, keep training smart.
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Disclaimer: I occasionally mention brands and products but it is important to know that I am not affiliated with, sponsored by, an ambassador for, or receiving advertisement royalties from any brands. I have conducted biomedical research for which I have received research money from publicly-funded national research councils and medical charities, and also from private companies, including Novo Nordisk Foundation, AstraZeneca, Amylin, A.P. Møller Foundation, and Augustinus Foundation. I’ve also consulted for Boost Treadmills and Gu Energy on their research and innovation grant applications and I’ve provided research and science writing services for Examine — some of my articles contain links to information provided by Examine but I do not receive any royalties or bonuses from those links. These companies had no control over the research design, data analysis, or publication outcomes of my work. Any recommendations I make are, and always will be, based on my own views and opinions shaped by the evidence available. My recommendations have never and will never be influenced by affiliations, sponsorships, advertisement royalties, etc. The information I provide is not medical advice. Before making any changes to your habits of daily living based on any information I provide, always ensure it is safe for you to do so and consult your doctor if you are unsure.
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About the author:
I am Thomas Solomon and I'm passionate about relaying accurate and clear scientific information to the masses to help folks meet their fitness and performance goals. I hold a BSc in Biochemistry and a PhD in Exercise Science and am an ACSM-certified Exercise Physiologist and Personal Trainer, a VDOT-certified Distance running coach, and a Registered Nutritionist. Since 2002, I have conducted biomedical research in exercise and nutrition and have taught and led university courses in exercise physiology, nutrition, biochemistry, and molecular medicine. My work is published in over 80 peer-reviewed medical journal publications and I have delivered more than 50 conference presentations & invited talks at universities and medical societies. I have coached and provided training plans for truck-loads of athletes, have competed at a high level in running, cycling, and obstacle course racing, and continue to run, ride, ski, hike, lift, and climb as much as my ageing body will allow. To stay on top of scientific developments, I consult for scientists, participate in journal clubs, peer-review papers for medical journals, and I invest every Friday in reading what new delights have spawned onto PubMed. In my spare time, I hunt for phenomenal mountain views to capture through the lens, boulder problems to solve, and for new craft beers to drink with the goal of sending my gustatory system into a hullabaloo.
Buy me a beer. 
Because, while starting exercise hypohydrated will likely manifest a performance detonation, you’ll likely be totally fine if you start exercise euhydrated. 
Because larger weight loss during exercise is not correlated with poorer performance and because weight loss during exercise does not necessarily indicate that total body water has decreased. 
Because under “normal” ambient conditions (<25°C), a 2% weight loss during exercise has negligible effects on performance and most people can tolerate up to 3-4% (some as much as 9%!) weight loss before performance declines. Weight loss during exercise (as a biomarker for dehydration) is only associated with impaired endurance performance in hot conditions — i.e. dehydration typically only impairs performance when your need to cool down is imperative. 
Because when drinking to replace all sweat losses during exercise (aka planned “drinking to a schedule”) you might hyperhydrate and cause hyponatremia. 
Because thirst is our only “biomarker” indicating that we need to drink, and “drinking to thirst” (or ad libitum drinking) can maintain hydration status, even during ultra-distance races in the heat (i.e. above ~25°C). And, 
Because sodium supplementation (and/or sodium preloading) is generally unnecessary for maintaining plasma sodium concentrations and performance and likely only becomes “necessary” during very long duration races if you have a high sweat rate with a high sweat sodium concentration.
Under cool to warm conditions (<25°C), the average runner drinks ~380 mL/h. 
How can you manage your hydration on race day?
Learn. Plan. Practice.
