Is Hydration Just as Important as Your Carb Intake?

Is Hydration Just as Important as Your Carb Intake?

by | Nov 23, 2025 | Nutrition, Uncategorized

By Sandi Nypaver
Special thanks to Dina Griffin, MS, RDN, CSSD for reviewing scientific accuracy

Most runners understand the importance of carb intake during training and racing. What fewer people realize is that your hydration plan is just as important. In real-world endurance events, both performance and gut tolerance often fall apart not because athletes fail to eat enough, but because they become dehydrated or mismatched their sodium intake to their own sweat profile.

Hydration is not a one-size-fits-all strategy. Your sweat rate and sweat sodium concentration are unique to you, and these values play a major role in how well your body regulates temperature, absorbs fluids, fuels your muscles, and maintains steady blood volume during training and racing.

My goal with this article is to help you understand why hydration matters just as much as carbohydrates, how your sweat is uniquely yours, and how you can build your own personalized hydration strategy for better performance and fewer GI issues.

What Happens When You Get Dehydrated?

Even mild dehydration affects performance. As fluid loss accumulates, the following changes occur:

  • Thermoregulation becomes harder which increases core temperature
  • Sweat rate decreases which makes cooling less efficient
  • Blood volume drops which reduces the oxygen and nutrients delivered to working muscles
  • Heart rate rises to compensate for reduced plasma volume
  • Perceived effort increases at the same pace or power
  • Mental sharpness declines
  • Severe dehydration can lead to low blood pressure and dizziness
  • Kidney perfusion decreases which increases the risk of rhabdomyolysis
  • Carbohydrate metabolism becomes less efficient because glycogen breakdown requires water

These physiological changes do not happen in isolation. They compound. The result is a slower pace, earlier fatigue, and a higher chance of GI issues. Even the best fueling plan cannot overcome the impacts of dehydration.

Why Your Sweat Loss and Sodium Needs Are Unique

Two key variables define your hydration needs.

Sweat rate

This is how much fluid you lose per hour.
Typical ranges vary dramatically.
Some athletes lose 0.5 liters per hour while others lose 2.5 liters per hour in the same conditions.

Sweat rate also changes with:

  • Air temperature
  • Humidity
  • Intensity
  • Heat acclimation
  • Clothing and gear
  • Running surface and solar load
  • Your hydration status going into the session

This is why repeated testing in different conditions matters.

Sweat sodium concentration

This is how much sodium you lose per liter of sweat.
It is primarily genetically influenced and stays relatively stable for each athlete.

Ranges can be as low as 200 mg per liter or as high as 2000 mg per liter.
This is a ten-fold difference.

Heat acclimation and consistent training can reduce sweat sodium concentration slightly because the body becomes more efficient at reabsorbing sodium in the sweat glands. However, these changes are moderate. An athlete losing 1400 mg per liter will not suddenly become a 300 mg per liter athlete through training alone.

Understanding your personal sodium concentration is one of the most powerful steps you can take to avoid both under-replacement and over-salting during long events.

Understanding Sodium’s Role

Sodium supports performance in several important ways.

• Helps maintain blood volume
• Supports fluid absorption in the small intestine
• Prevents excessive dilution of blood sodium during long events
• Helps preserve neuromuscular function
• Improves palatability of drinks which encourages adequate intake

Sodium does not prevent cramping on its own but it supports the whole system in a way that reduces the conditions where cramps are more likely.

How Much Dehydration Can You Tolerate?

It is often recommended that endurance athletes try to keep body mass losses within 2 to 4 percent during long events. For many athletes, losses beyond this range are associated with greater performance impairment and an increased risk of heat-related issues.

However, well trained or well heat adapted athletes sometimes tolerate losses up to 5 to 6 percent without significant performance decline. These athletes are the exception, not the rule. For most runners, even modest dehydration feels noticeably harder.

What matters most is understanding your own tolerance and planning hydration so fluid loss stays within your safe range.

See how mine and Sage’s sweat test with the Nutrition Mechanic went!

An Example of How Hydration Can Go Wrong

Imagine a runner with the following sweat profile:
Sweat sodium concentration. 350 mg per liter
Sweat rate. 1 liter per hour in 75 degree dry heat

Their race-day plan looks like this:
Fluid intake: 0.5 liters per hour
Sodium intake: 750 mg per hour

Where the problems begin:

This athlete is losing 1 liter of sweat per hour but drinking only half that amount. This creates a fluid deficit of 0.5 liters every hour. Over ten hours, this would be an estimated eleven pounds of body weight lost. Even accounting for glycogen use and metabolic weight changes, this is well beyond the range most athletes can tolerate without a significant decline in performance.

At the same time, the athlete is consuming more sodium per hour than they are losing through sweat. Combined with dehydration, this increases blood sodium concentration and raises the risk of hypernatremia, which occurs when sodium levels in the blood become too high.

This example shows why pairing high-sodium products with insufficient fluid intake can create problems even for low sodium sweaters.

A Second Practical Example. Why Two Runners Can Need Completely Different Sodium Amounts

Two runners head out for the same three hour long run.
They run at similar intensities and sweat the same amount.
Their sweat rate is 0.7 liters per hour which equals a total of 2.1 liters of sweat lost.

The only major difference between them is their sweat sodium concentration.

Runner A
Sweat sodium concentration. 450 mg per liter
Total sodium lost. 945 mg

Runner B
Sweat sodium concentration. 1300 mg per liter
Total sodium lost. 2730 mg

Even though they ran side by side and sweated the same volume, Runner B lost almost three times as much sodium.

Sports dietitians generally recommend replacing about 50 to 80 percent of sodium lost during longer training sessions and races.

Which means:

Runner A typically needs 470 to 750 mg total
Runner B typically needs 1360 to 2180 mg total

Their hydration plans should look completely different.

Runner A may do well with a moderate sodium drink mix or occasional electrolytes.
Runner B may need a higher sodium concentration or more frequent electrolyte intake to maintain blood sodium levels, support fluid absorption, and keep performance steady.

This example shows why knowing your sweat sodium concentration helps you avoid both under-salting and over-salting. Two athletes can run the same route, in the same weather, at the same pace, yet require very different hydration strategies.

A Note on Lab Tests vs Real-World Wearables

In fall 2024, I completed a Precision Hydration sweat test and received a baseline result of 573 mg of sodium per liter. This value represents my physiology under controlled conditions. Since then, I have used the hDrop hydration sensor during more than ten training runs, where it consistently reports 850 to 1050 mg/L.

Precision Hydration’s internal testing shows that hDrop tends to overestimate sodium by about 170 mg/L and underestimate sweat rate by about 0.5 L/h. Sweat sodium concentration also naturally increases during harder or hotter sessions because sweat glands have less time to reabsorb sodium.

When adjusting for device tendencies and real-world intensity, my “working” sweat sodium concentration during training is likely closer to 650 to 900 mg/L.

For my own strategy, I use:
• Lab value (573 mg/L) in cooler or moderate sessions
• Adjusted range (650 to 900 mg/L) in heat or higher-intensity conditions
• Upper range approaches ~1000 mg/L only in demanding long runs in hot weather

Both the lab test and the wearable data are helpful. Trends across conditions matter more than any single number.

Hyponatremia

Hyponatremia is a condition where blood sodium levels drop too low. While athletes often worry about not getting enough sodium, hyponatremia is far more commonly caused by drinking more fluid than you are losing, especially when that fluid is mostly plain water.

When you overconsume fluid relative to your sweat rate, blood sodium becomes diluted. Symptoms can include nausea, headache, swelling in the hands or face, confusion, and in severe cases seizures or loss of consciousness.

Hyponatremia does not develop from failing to consume high amounts of sodium. It develops when fluid intake exceeds your body’s ability to clear that fluid. This is why knowing your sweat rate is just as important as knowing your sweat sodium concentration. Matching both appropriately keeps you in a safe and optimal range.

How to Figure Out Your Individual Hydration Needs

Step 1. Determine your sweat sodium concentration

A professional sweat test provides individualized data that rarely shifts outside of moderate heat adaptation. Wearables such as the hDrop can provide useful trend data during real-world training.

Typical ranges

  • Low. 200 to 700 mg/L
  • Moderate. 700 to 1100 mg/L
  • High. 1100 to 1500 mg/L
  • Very high. 1500 to 2000+ mg/L

This number helps guide sodium intake rather than relying on generic recommendations.

See how mine and Sage’s sweat test with Dina Griffin went here.

Step 2. Measure your sweat rate in different conditions

The simplest and most accurate way to measure sweat rate is by weighing yourself before and after training.

  • Weigh yourself naked before your run
  • Track all fluid intake
  • Weigh yourself naked again after your run
  • Subtract post-run weight from pre-run weight
  • Add the amount of fluid consumed
  • Subtract urine output if applicable
  • Divide by hours exercised

Sweat rate = fluid lost per hour.

It is helpful to repeat this in several environments since sweat rate changes significantly with temperature, humidity, and intensity.

You can also use wearable devices such as the hDrop hydration sensor to gather sweat rate data. These devices can provide real-time estimates, though it is still valuable to compare wearable data with the pre- and post-run weigh-in method for accuracy.

Here is the Nutrition Mechanic sweat rate spreadsheet to make tracking easier:
https://nutritionmechanic.mykajabi.com/sweatrate

Step 3. Estimate your hourly losses

Once you know your sweat sodium concentration and your sweat rate, you can estimate what you typically lose during training.

Fluid loss per hour
This is simply your sweat rate.
If your sweat rate is 1 liter per hour, then you lose about 1 liter of fluid per hour.

Sodium loss per hour
Multiply your sweat sodium concentration (mg/L) by your sweat rate (L/hour).
For example, if you lose 700 mg per liter and you sweat 1 liter per hour, you lose about 700 mg of sodium per hour.

These hourly estimates do not need to be perfect. They simply give you a clearer sense of your typical losses so you can match your fluid and sodium intake more effectively.

Step 4. Match intake to your needs

General guidelines used by many sports dietitians:

For long events
Replace about 50 to 80 percent of sodium lost

Fluid replacement
Usually 60 to 90 percent of sweat rate depending on conditions and GI tolerance

Most sports drinks
Contain 400 to 1000 mg of sodium per liter

More on why you should not aim for 100 percent like-for-like fluid replacement can be found here.

Step 5. Practice in training

Practice combinations of:

  • Fluid volume
  • Sodium concentration
  • Drinking frequency
  • Fuel timing

Your best race-day plan is built through consistent training, not guesswork.

Common Hydration Mistakes

Assuming more sodium is always better
Drinking too little because carrying bottles feels inconvenient
Using the same plan year round
Overdrinking plain water which increases hyponatremia risk
Using drink mixes that exceed your sodium needs
Not practicing high fluid intake in training
Trying new products on race day

Understanding the Hydration and Carbohydrate Connection

Carbohydrate metabolism requires water.
If you are dehydrated, your muscles have less access to stored carbohydrate and your gut becomes less efficient at absorbing fuel. This is why dehydration often feels like “my stomach shut down” even when carb intake is appropriate.

Your hydration and fueling plans work together.

Final Thoughts: Why This Matters

Hydration is not secondary to carbohydrates. They are equal partners in performance. Understanding your sweat rate and sweat sodium concentration gives you the tools to create a personalized hydration strategy that supports your training, keeps you safe, and helps you perform at your best.

Taking time to get hydration right pays off on every long run and every race.

If this article helped you, sharing it supports our ability to keep offering free education through Higher Running.

Sandi, Dina , & Sage after sweat testing

Resources:
Dina Griffin’s website: Nutrition Mechanic
Find a sweat test near you: Sweat Testing Locations (Or just do a quick internet search!) Dina is a great choice if you’re in or near Boulder, CO. Sage and I drove 3 hours just to see her.

https://pubmed.ncbi.nlm.nih.gov/12834575/

American College of Sports Medicine position stand. Exercise and fluid replacement

Exercise-induced hypohydration impairs 3 km treadmill-running performance in temperate conditions

Dehydration and endurance performance in competitive athletes

Drinking behaviors of elite male runners during marathon competition

How much dehydration can you tolerate?

How to Make Every Training Block Count

How to Make Every Training Block Count

by | Nov 6, 2025 | Uncategorized

Your speed work should evolve as race day gets closer!

Coach Sandi Nypaver breaks down a concept used by many coaches—and by runners who coach themselves—is that your training should become more specific as you go.

For example, if your goal race is a marathon, you might start off (after establishing a good aerobic base) with some easy mileage, strides, and maybe a few fartleks. Then, your first block of structured training could focus more on 5K or 10K–specific work. That means shorter, faster intervals. You might still include tempo runs, but they wouldn’t be the main focus in this phase.

Your next training block would shift toward more lactate threshold work—that’s what I mean by tempo runs. These efforts are around one-hour race pace, or for some runners, even half-marathon–specific workouts.

Finally, in the last block of training—roughly the final six to eight weeks leading up to your marathon—you’d focus on marathon-specific work. Your key workouts would include long runs with segments at or around marathon pace.

That’s the overall concept: your training becomes more specific to your goal race as you progress through each phase.

Aerobic Base Training: Why Runners Do It

Aerobic Base Training: Why Runners Do It

by | Nov 3, 2025 | Uncategorized

 

We focus on aerobic base training mainly because it’s safer and more sustainable for long-term improvement. It’s not so much about your heart rate going over a certain number, like your max heart rate or dipping into Zone 3, that’s the issue. The bigger concern is the stress on your musculoskeletal system: your tendons, bones, and ligaments. These tissues are more fragile and take longer to adapt than your cardiovascular system.

When runners train too fast on easy days, slipping into Zone 3 or Zone 4 instead of staying in Zone 2, they increase the impact forces with every step. That added stress can lead to overtraining or injury.

There’s also the mental side. It’s exhausting to push hard and experience discomfort every day. You don’t want that imbalance in your training as both your body and mind need easier days to recover and adapt!

The third and final reason we emphasize Zone 2, low-intensity running is consistency. When you stay at a lower intensity, you’re less likely to get injured, and it’s mentally easier to keep showing up day after day. That consistency allows you to build more total volume- running longer, covering more distance, and training more frequently.

And that’s where the balance comes in. Higher-intensity running actually creates a stronger stimulus for many aerobic adaptations. Things like increased mitochondrial density, improved running economy, and higher VO₂ max. But because those harder efforts take more out of you, they can’t be done every day. Lower-intensity running lets you train more consistently and build the overall volume that supports those adaptations and makes the harder sessions more effective.

The beauty of lower-intensity, aerobic-based training is that it lets you run more, more often, and more consistently and that’s what truly makes you a stronger, faster, and more efficient runner.

The Repeated Bout Effect & Eccentric Loading

The Repeated Bout Effect & Eccentric Loading

by | Oct 23, 2025 | Uncategorized

The repeated bout effect describes how your body becomes better at handling a specific type of stress it has already experienced (Nosaka and Clarkson 1995).

When you do a hard or unfamiliar workout, like a long downhill run, your muscles experience microscopic damage and inflammation. The next time you do something similar, your body remembers that stress and adapts through structural, neural, and connective tissue changes, so you do not get as sore or fatigued (Hyldahl, Chen and Nosaka 2017). For downhill workouts in particular, this adaptation can last for several weeks, which is why you only need to do faster downhill sessions about every two weeks or even less often, depending on your race needs. The benefits tend to last longer than those from most other types of training stress (Chen, Nosaka and Tu 2021).

Downhill running places a high eccentric load on your muscles, especially the quadriceps, which control your descent and stabilize your knees under increased impact forces (Eston, Mickleborough and Baltzopoulos 2019). Instead of pushing you forward, they act like brakes to maintain control and prevent knee collapse. This braking role becomes even more important on steep or extended descents, where both pace and impact forces are higher.

Doing strength work that includes eccentric exercises may help your muscles absorb force more effectively and reduce muscle damage in future sessions (Douglas, Pearson, Ross, and McGuigan 2017). For road or trail runners who struggle to get in as much climbing and descending as their races demand, eccentric strength training and some targeted downhill running can help ensure their legs hold up in the later stages of a race.

A Simple Strength Routine

Try including these exercises when you want to prepare your legs to resist fatigue at the end of a race:

  • Step-downs from a low box or step, lowering slowly for three to four seconds, 8-10 reps per leg
  • Slow Bulgarian split squats, lowering for three seconds, 8-10 reps per leg
  • Single-leg Romanian deadlifts, focusing on control during the lowering phase, 8-10 reps per leg
  • Optional wall sits or slow walking lunges for extra quad endurance

If this is your first time doing eccentric strength work, start easy. The goal is to feel the muscles working, not to push to failure. Move slowly and with control, keeping effort around five to six out of ten, and stop well before you feel fatigue. Even one set per exercise is enough for the first week. Mild soreness is normal, but if it lasts more than a couple of days, reduce the load next time. If you are already used to lifting, you can work at a higher load with fewer reps, like four to six, while keeping the focus on slow, controlled lowering.

Focus on Form

Good form is everything. Poor form reinforces bad movement patterns and increases injury risk. Control the movement through the full range, keep your knees tracking over your toes, and maintain a neutral spine. If you feel pain in your knees or lower back, adjust your form or reduce the load. Find tips for good form here.

Downhill Running

Downhill running is an excellent way to condition your legs for descents and build the resilience needed to stay strong late in a race. However, because downhill running increases impact and muscle stress, it is best reserved for runners who are healthy and injury-free.

Aim to include a faster downhill session about every two to two and a half weeks during the final six weeks before your race, with the last one roughly two weeks before race day. Depending on your race profile and how much eccentric strength work you are doing, one or two downhill sessions may be plenty. For some runners, simply doing a lot of vertical gain and including a few moderately fast downhills may be enough. Here are some examples of what that could look like.

For road marathoners without access to big hills: You can simulate downhill stress by running a short, controlled downhill segment at near top speed. For example, run a 1-minute downhill effort five to eight times at the end of a long run. Focus on good form and maintaining control rather than pure speed.

For ultra runners tackling a mountain hundred: Include a runnable but somewhat steep downhill in a long run, aiming to descend two thousand or more feet if your terrain allows. Run at a fast but controlled pace that challenges your quads and downhill mechanics without risking form breakdown or injury. Adjust distance and intensity based on what your race course will demand and how fatigued you are from the rest of the run.

Bringing It All Together

Downhill running and eccentric strength work are just one small part of your training picture. Consistency, building volume, training specificity, and hitting the right workouts at the right time are what really make the difference. Combining controlled downhill running with eccentric strength training helps your muscles adapt and become more resilient, allowing you to handle descents, long road stretches, or the final miles of an ultra with less fatigue and soreness.

Plan your final hard downhill or eccentric strength session about two weeks before race day so your legs have time to recover and adapt. You will show up strong, fresh, and ready to roll.

References

Chen, T. C., Nosaka, K., and Tu, J. H. 2021. Changes in muscle damage markers and repeated bout effect after different eccentric exercise protocols. Frontiers in Physiology, 12, 654

Douglas, J., Pearson, S., Ross, A., and McGuigan, M. 2017. Eccentric exercise: Physiological characteristics and acute responses. Sports Medicine, 47(4), 663–675

Eston, R. G., Mickleborough, J., and Baltzopoulos, V. 2019. Eccentric exercise-induced muscle damage and adaptation. Strength and Conditioning Journal, 41(2), 31–39

Hyldahl, R. D., Chen, T. C., and Nosaka, K. 2017. Mechanisms and mediators of the repeated bout effect. Exercise and Sport Sciences Reviews, 45(1), 24–33

Nosaka, K., and Clarkson, P. M. 1995. Muscle damage following repeated bouts of high force eccentric exercise. Medicine and Science in Sports and Exercise, 27(9), 1263–1269

Why Every Runner Should Be Doing Strides!

Why Every Runner Should Be Doing Strides!

by | Oct 8, 2025 | Uncategorized

Coach Sage Canaday discusses about one of the simplest, most effective ways to improve your running without adding more mileage or intensity: Strides.

What Are Strides?

Strides are short accelerations, usually 100 meters or about 20 seconds, run at a pace faster than your 5K race pace, but not quite an all-out sprint.

They’re smooth, controlled, and focused on form, not effort. Think of them as a hybrid between a drill and a mini speed burst.

Why Do Strides?

Whether you’re training for a marathon, an ultra, or just trying to stay fit, strides offer a ton of benefits:

  • ✅ Improve running economy (how efficiently you run)

  • ✅ Enhance technique (foot strike, arm swing, posture)

  • ✅ Build speed and power without high stress

  • ✅ Activate fast-twitch muscle fibers, even if you’re a slow-twitch specialist

Even though my form isn’t perfect, I started doing strides 25 years ago. As a slow-twitch marathoner, I once ran a 3:55 for 1500m (that’s a 4:15 mile!) 🙌

How to Add Strides to Your Week

Here’s how to keep it simple:

After Easy Runs (2–3x/week):

  • 4 × 100m strides (or 4 × 20 seconds)

  • Walk or jog for 60–90 seconds between each

  • Focus on relaxed, smooth form — not max effort

Before Speed Workouts:

  • Use strides after your warm-up jog to prime your body for intensity

A Quick Word on Safety

Strides should feel energizing, not exhausting. Ease into them gradually to avoid injury. Think of them as a form drill, not a race.

Keep your posture tall, arms swinging naturally, and feet landing under your center of mass.

 Final Thought

Strides are the secret sauce to becoming a more efficient, powerful, and confident runner. They take just a few minutes, but the payoff is huge.

So next time you finish an easy run, throw in a few strides — your future self will thank you!

The Best Way To Train For A Race

The Best Way To Train For A Race

by | Oct 8, 2025 | Uncategorized

Coach Sandi Nypaver discusses what matters when training for a race.
     
Photo Credit: Luke Webster

 

 

I’ve always enjoyed looking at the training of professional runners and the recurring theme is that while there are similarities, there are also some significant differences. This is especially true when looking at elite trail and ultra runners.

If you were to look at the training of the past 10 winners of the Boston Marathon, you’d see both similarities and major differences. The same is true for races like Western States. While there are certainly best practices, there’s no single “best” way to train that works for everyone.

Some runners even find that a method of training works well for years—until suddenly it doesn’t. At that point, something has to change for progress to continue. Among elite road runners, you’ll see not only different types of workouts but also very different ways of organizing them within a training cycle.

When it comes to elite trail runners—or runners in general—the variety only widens. Weekly mileage and elevation gain can look drastically different, even for athletes preparing for the same exact race.

As a coach, I have my own training philosophy, but I also take into account many factors. I look for where a runner has the most room to improve, whether the race profile requires specific adjustments, and when it might be more beneficial for an athlete to simply repeat a similar training cycle to build confidence and consistency.

Just as important as the training itself is trust—trust in the process and in your coach. If you don’t believe in what you’re doing, it’s much harder to reap the benefits. You’ve got to enjoy what you’re doing. If you’re not enjoying it, you might have success for awhile, but that success isn’t going to last.

For me, good coaching isn’t about declaring myself “the best” or trying to establish authority. It’s about recognizing that there are multiple effective ways to train—and then helping each runner find the right path for them.