Right here’s a stat that may shock you: Within the 2002 Boston Marathon, 13% of finishers developed hyponatremia, a probably deadly situation induced not by ingesting too little, however by ingesting an excessive amount of plain water.
That’s proper. The hazard wasn’t dehydration.
This discovering turned many years of hydration recommendation on its head and uncovered a basic drawback with one-size-fits-all suggestions.
The reality is, your hydration wants as a runner have virtually nothing to do with the generic “8 glasses a day” rule you’ve heard since childhood.
In the event you’re a runner coaching for something from a 5K to a marathon, you want a unique method, one based mostly in your particular person sweat fee, sodium losses, environmental situations, and race distance.
This text will present you tips on how to transfer past generic hydration myths and construct a personalised, evidence-based technique that really works.
You’ll learn to…
Measure your sweat fee
Perceive electrolyte wants
Forestall each dehydration and the damaging entice of overhydration
Regulate your method for various climates and distances
As a result of getting hydration proper isn’t nearly efficiency, it’s about security.
The Deadly Flaw in Common Hydration Pointers
The “8 glasses of water per day” advice wasn’t created with runners in thoughts.
It was developed for sedentary adults residing in temperate climates.
Analysis printed within the Worldwide Journal of Sport Vitamin and Train Metabolism [1] discovered that operating lower than 60 minutes per day will increase your each day fluid wants by an element of 1.3, whereas operating greater than 60 minutes per day will increase wants by 1.9 to 2.3 instances your baseline.
However right here’s what makes common suggestions actually problematic: particular person sweat losses amongst runners vary from roughly 0.2 to five.0 liters per day, a 25-fold distinction.
That’s not a typo.
Your coaching companion may lose 5 instances extra fluid than you throughout the identical run, that means their hydration wants are utterly completely different.
A research of leisure tropical runners [2] discovered that male runners usually sweat at a fee of 1.3 ± 0.5 L/hr, whereas feminine runners common 0.9 ± 0.3 L/hr.
However inside every group, the variation is gigantic.
Some runners lose lower than 0.5 L/hr whereas others exceed 2.5 L/hr below related situations.
Your physique dimension, muscle mass, warmth acclimatization standing, operating tempo, clothes, and genetics all affect your sweat fee.
When Dehydration Truly Impairs Efficiency
Earlier than we obsess over changing each drop of sweat, let’s look at what the analysis truly says about dehydration and efficiency.
A complete evaluation in Physiological Evaluations [3] confirms that dehydration exceeding 2% of physique weight can impair cardio train capability, notably in heat environments.
Dropping greater than 1% of physique weight by means of dehydration can also impair cognitive operate, your potential to tempo accurately, make tactical selections, and acknowledge when one thing’s unsuitable.
However right here’s the nuance most hydration recommendation misses: most marathoners routinely end races having misplaced 3% to almost 10% of their physique weight.
Alberto Salazar famously misplaced 8.1% of his physique weight (5.43 kg) through the 1984 Olympic Marathon regardless of ingesting 1.88 liters through the race, and his sweat fee was measured at a unprecedented 3.71 liters per hour.
The important thing isn’t stopping all weight reduction, it’s beginning well-hydrated and understanding your private tolerance.
Research of elite marathoners [4] on the 2019 World Championships confirmed that 93% had pre-planned hydration methods, however private expertise was the first determinant of their method, not generic formulation.
These athletes drank roughly 550 ± 340 mL/hr advert libitum (to thirst), and sooner performances had been truly related to higher weight reduction.
This doesn’t imply it is best to purpose for optimum dehydration, but it surely demonstrates that average fluid deficits don’t essentially destroy efficiency.
Measuring Your Particular person Sweat Fee
If you would like customized hydration steering, you must measure your precise sweat losses.
The at-home sweat check is remarkably easy and supplies actionable information.
Runner’s World printed a validated protocol [5] that works like this:
First, empty your bladder and weigh your self nude earlier than your run.
Document this weight exactly.
Run at your goal race tempo for precisely one hour, protecting cautious monitor of how a lot fluid you devour through the run.
After ending, towel off any sweat and weigh your self nude once more.
The calculation is simple: (Pre-weight minus Put up-weight) plus Fluid consumed equals Whole sweat loss.
For instance, for those who misplaced 1 pound (16 oz) and drank 16 oz of fluid, your complete fluid loss was 32 oz, supplying you with a sweat fee of 32 oz per hour.
Divide by 4 to find out it is best to drink roughly 8 oz each quarter-hour to match losses.
However right here’s the crucial half: you must repeat this check below numerous situations.
Your sweat fee on a cool morning in February will differ dramatically from a moist afternoon in August.
Sports activities science analysis [6] signifies that something under 0.5 L/hr is comparatively low for race intensities in gentle situations, whereas charges exceeding 2.5 L/hr create important challenges for sustaining hydration throughout extended train.
Check at completely different paces, as a result of depth straight impacts sweat fee.
Check in situations just like your aim race, identical temperature, humidity, time of day.
Physique dimension issues too, a 6’2″ male weighing 180 kilos may have completely different baseline charges than a 5’4″ feminine weighing 120 kilos, even when they run the identical tempo.
The Sodium Story: Extra Than Easy Dehydration
Water isn’t the one factor you lose whenever you sweat.
Sodium is the first electrolyte misplaced throughout train, and its position extends far past stopping muscle cramps.
Sodium is crucial for sustaining plasma quantity and blood stress, selling fluid retention, and enabling correct mobile hydration.
A complete research within the Journal of Sports activities Sciences [7] analyzed 1,303 athletes and located important sport-specific variation in sodium losses, with endurance athletes displaying among the highest charges.
Male runners lose roughly 54 ± 27 mmol/hr of sodium, whereas females common 39 ± 22 mmol/hr.
For context, sweat sodium focus in athletes usually ranges from 20-80 mmol/L.
In the event you’re a “salty sweater”, you discover white residue in your clothes or pores and skin after runs, you’re possible on the upper finish of this spectrum.
The analysis staff concluded that American soccer gamers and endurance athletes have the best want for deliberate hydration methods as a consequence of substantial variation in each whole-body sweat fee and fee of sodium loss.
Right here’s why sodium issues a lot: whenever you drink giant volumes of plain water with out satisfactory sodium alternative, you dilute the sodium focus in your bloodstream.
This creates a harmful situation referred to as exercise-associated hyponatremia.
The Hidden Hazard: Train-Related Hyponatremia
The landmark research printed within the New England Journal of Medication [8] examined 488 Boston Marathon finishers and located that 13% had hyponatremia (blood sodium under 135 mmol/L), with 0.6% having crucial hyponatremia under 120 mmol/L.
Since that 2005 research, consciousness has elevated, however the issue persists.
A scientific evaluation within the Journal of Scientific Medication [9] of marathon research discovered prevalence charges starting from lower than 1% to 22%, with a mean of 8.2 ± 7.9%.
In ultramarathons, the incidence skyrockets, analysis in Frontiers in Vitamin [10] discovered 65% of finishers in a 246-km race developed both gentle or extreme hyponatremia.
The first trigger isn’t insufficient sodium consumption, it’s extreme fluid consumption relative to sodium losses.
A 2017 evaluation in Frontiers in Medication [11] constantly exhibits that overdrinking past thirst and non-osmotic arginine vasopressin launch are the commonest mechanisms.
Weight achieve throughout a race is the strongest predictor of hyponatremia.
Who’s at highest danger?
Slower runners who spend greater than 4 hours on the course have extra alternatives to overdrink.
Smaller athletes might devour bigger volumes relative to their dimension.
Feminine runners seem extra vulnerable, although this can be confounded by physique dimension and ending time reasonably than intercourse per se.
First-time marathoners typically observe aggressive hydration schedules with out understanding their particular person wants.
Maybe most surprisingly, one research discovered that 14% of ultramarathon contributors began the race already mildly hyponatremic, they’d over-hydrated within the days main as much as the occasion.
The signs progress from nausea, headache, and confusion to vomiting, altered consciousness, and in extreme instances, seizures and demise.
Eight deaths from exercise-associated hyponatremia have been documented since 1985.
Right here’s the crucial level: sodium supplementation alone gained’t stop hyponatremia for those who’re overdrinking.
A case report in the identical Frontiers in Medication evaluation [12] described a runner with prior EAH who consulted a sports activities nutritionist and consumed appreciable supplemental sodium, but nonetheless developed symptomatic hyponatremia throughout a subsequent future.
The quantity of fluid, not the quantity of sodium, consumed throughout train determines last blood sodium concentrations.
The answer is elegantly easy: drink to thirst.
Your physique’s suggestions mechanisms work remarkably effectively for those who don’t override them by following inflexible ingesting schedules.
Local weather-Particular Hydration Methods
Environmental situations dramatically have an effect on your hydration wants, but most runners use the identical method year-round.
Temperature issues, however humidity is the crucial variable most individuals underestimate.
Analysis printed within the journal Temperature [13] examined completely different humidity ranges and located that exercising at 61% and 71% relative humidity produced considerably larger core temperatures and coronary heart charges in comparison with 23% humidity, even on the identical temperature.
The mechanism is simple: sweat solely cools you when it evaporates.
In humid situations, the air is already saturated with water vapor, which dramatically reduces evaporation charges.
Sweat that drips off your physique with out evaporating supplies zero cooling, it’s referred to as “non-productive sweating.”
Research in Vitamins [14] analyzing tropical climates present that runners in heat, high-humidity environments face compromised evaporative cooling, resulting in decrease charges of physique warmth dissipation regardless of related sweat charges to temperate-climate runners.
The average optimistic correlation between pre-exercise urine particular gravity and fluid consumption, mixed with the average unfavourable correlation between pre-exercise hydration standing and whole-body sweat loss, means that pre-existing gentle dehydration may very well impair thermoregulatory operate.
This will increase warmth sickness danger in scorching climates.
In sensible phrases: for those who’re operating a marathon in Florida humidity versus a dry desert race in Arizona, your hydration technique wants adjustment even when the temperatures are similar.
Sizzling-humid situations require beginning notably well-hydrated, starting fluid consumption earlier within the race, and being extra conservative with pacing.
Sizzling-dry situations permit for larger sustainable sweat charges, some heat-acclimatized athletes can preserve 2-3 L/hr—however the fast evaporation might masks how a lot fluid you’re truly shedding.
Sensible Hydration by Distance
Your race distance basically modifications your hydration wants.
For 5K to 10K races lasting below 45 minutes, pre-race hydration standing issues excess of ingesting through the occasion.
The analysis on operating durations [15] discovered that runners finishing efforts below 60 minutes typically required no fluid consumption to stop important dehydration earlier than run completion.
Concentrate on being well-hydrated within the 24 hours earlier than the race, pale yellow urine colour is your goal.
Eat 16-20 oz of fluid 2-4 hours earlier than the beginning, then small sips as much as half-hour prior.
Keep away from overdrinking, which creates that uncomfortable sloshing sensation that impairs efficiency.
Half marathons characterize the transition zone the place hydration turns into extra necessary.
With durations between 1.5-2.5 hours for many runners and sweat losses of 1-3 liters, you’ll wish to begin ingesting round 30-40 minutes into the race.
The American School of Sports activities Medication recommends 0.4-0.8 L/hr for many athletes.
Goal taking fluids at each different support station, about 2-4 oz per cease reasonably than full cups, and select sports activities drinks with sodium reasonably than plain water.
Marathons require complete hydration administration because of the 3-5+ hour period for many runners, with potential sweat losses of 2-6 liters and important sodium losses exceeding 3-4 grams.
Observational research of elite marathoners present they drink roughly 550 ± 340 mL/hr to thirst, and none observe inflexible schedules to exchange all sweat losses.
For leisure runners, purpose for 0.4-0.8 L/hr adjusted on your measured sweat fee, use sodium-containing drinks all through, and begin ingesting early at mile 3-5.
The important thing precept: don’t purpose for zero weight reduction.
A 2-3% physique weight reduction is suitable and regular.
Sooner runners typically tolerate extra dehydration with out efficiency decrement.
Consuming past your sweat fee considerably will increase hyponatremia danger.
Constructing Your Personalised Plan
Shifting from idea to apply requires 4 concrete steps.
First, measure your sweat fee below situations just like your aim race.
Check in numerous temperatures, humidity ranges, and paces to construct an entire image.
Second, assess whether or not you’re a salty sweater by searching for white residue on clothes after runs.
If sure, prioritize sodium-containing drinks.
Third, set up baseline habits: monitor urine colour each day (pale straw yellow signifies good hydration), weigh your self on the identical time every morning to trace day-to-day hydration standing, and begin every run well-hydrated reasonably than attempting to catch up throughout train.
Fourth, apply your race-day technique throughout coaching runs.
By no means attempt new hydration approaches on race day.
Check completely different merchandise, concentrations, and timing to be taught your intestine tolerance.
The most typical errors to keep away from are following generic “drink each mile” recommendation, over-hydrating within the days earlier than a race, ignoring environmental situations when planning consumption, ingesting solely plain water on lengthy runs, and dramatically altering your technique on race day.
When race situations differ out of your coaching, unexpectedly scorching, operating slower or sooner than deliberate, GI misery, completely different altitude, be ready to regulate your method.
The science is unequivocal: hydration is very particular person.
Your sweat fee may differ from one other runner’s by an element of 5.
Your sodium losses may very well be double or half of your coaching companion’s.
The humidity and temperature on race day create distinctive calls for.
Generic suggestions fail as a result of they ignore this actuality.
By understanding your private physiology, testing your responses, and adjusting for situations, you’ll optimize each efficiency and security.
That’s the evidence-based method that strikes past the 8-glasses-a-day fantasy to one thing that really works for you.
