Why Summer Feels So Much Harder

June 24, 2026•4 min read

Why Summer Feels So Much Harder

Have you ever noticed how some days a run feels effortless and other days it feels like you're dragging an anchor behind you?

You check your watch. The pace is slower. Your heart rate is higher. The effort feels harder than it should. Sometimes your legs feel heavy before you've even gotten very far into the workout.

Most people assume they're losing fitness.

More often than not, they're simply under-fueled, under-hydrated, or not replacing the electrolytes they're losing through sweat.

As the temperatures rise this summer, your body has one primary goal: keep you cool. The way it does that is by producing sweat. When that sweat evaporates, it carries heat away from your body.

The problem is that sweat doesn't just contain water.

It contains electrolytes too, particularly sodium.

Every athlete loses a different amount. Some people lose very little. Others can lose well over 1,500 mg of sodium every hour. That's why one runner can get through a long run with a bottle of water while another starts cramping, slowing down, or feeling completely depleted despite drinking plenty.

Research has consistently shown that performance begins to suffer when dehydration reaches around 2% of body weight. For a 150-pound athlete, that's only about 3 pounds of fluid loss. It doesn't take very long to reach that point during a summer run, soccer tournament, baseball game, football practice, or even a day spent outside working in the yard.

The effects are often subtle at first.

Your pace slips a little.

Your heart rate creeps up.

The workout feels harder than normal.

You lose focus.

Your energy drops.

What makes this tricky is that many athletes try to solve the problem by simply drinking more water.

Water is important, but it isn't always the whole solution.

Think of it this way. If your truck was leaking oil, adding more gasoline wouldn't fix the problem. Your body works similarly. When you lose large amounts of sodium through sweat, replacing only water may not fully restore what your body needs to perform well.

This becomes especially important for endurance athletes, but it also applies to kids playing sports all summer.

One of the most common things I see is young athletes showing up to practice already behind. They haven't been drinking much during the day, they've been running around outside, and then they spend two more hours in the Alabama heat trying to play their sport.

By the time they feel thirsty, they're often already playing catch-up.

The same thing happens to adults.

I can't tell you how many runners have bad races and long runs and they think it must be electrolytes, carbs, or some other random variable. Sometimes the answer isn't a better training plan. Sometimes it's simply understanding what their body is losing and replacing it appropriately.

One of the easiest things you can do is figure out your sweat rate.

Weigh yourself before a one-hour workout. Track how much you drink. Then weigh yourself afterward.

Most runners are shocked when they discover how much fluid they actually lose in the summer. It's not uncommon for athletes in our area to lose 40, 50, or even 60+ ounces per hour during long runs in hot conditions.

Once you know your sweat rate, you can start making smarter decisions about hydration and electrolyte replacement instead of guessing.

The goal isn't to replace every drop of sweat you lose. The goal is to avoid digging yourself into a hole that becomes impossible to climb out of later.

If you've ever struggled with cramping, unusually high heart rates, heavy legs, poor recovery, or that feeling of completely running out of gas late in a workout or race, hydration and electrolyte balance are worth paying attention to.

The athletes who perform their best in the heat usually aren't the toughest. They're the ones who understand their bodies and prepare the smartest.

The sodium content in your sweat is specific to you and differs by a ton from person to person. We've tested and found people with as little as 400 mg/liter sodium loss to 2000 mg/liter sodium loss. Those people need two different and unique plans!

If you're curious about your personal sweat rate or sodium losses, we offer sweat testing at Return 2 Sport to help take the guesswork out of hydration. You will leave knowing the exact sodium to water ratio you need to crush your summer training.

Happy running,

R2S Team