Overtraining or Undereating? 🏃‍♀️

Dayna Player Robinson
Jul 7
3 min read

Overtraining or Undereating?

What’s Really Making Your Summer Runs Feel So Hard?

Have your runs felt extra sluggish lately?

Do you feel like your legs are heavy bricks by mile 2, your heart rate is higher than normal, you're not sleeping well, and your motivation is fading… even though you’re following your training plan perfectly?

You might think you’re “overtraining.”

But what if you’re actually under-eating?

☀️ Why Summer Training Feels Extra Hard

Running in the heat is already tough. According to the American College of Sports Medicine (ACSM), your heart rate increases by about 10 beats per minute for every 1°C (1.8°F) rise in core body temperature. Your body works harder to cool itself, shunting blood to the skin and away from working muscles, making each stride feel harder.

Add long miles, tough workouts, and sweat losses on top of that… and you’re at a higher risk of both overtraining syndrome and low energy availability.

🥵 What Is Overtraining Syndrome? 🥵

Overtraining syndrome happens when your training stress exceeds your body’s ability to recover, leading to:

Declining performance despite training harder
Persistent fatigue
Elevated resting heart rate
Mood changes (irritability, lack of motivation)
Poor sleep or disrupted recovery

Many runners assume this means they need more rest days or easier training. While that’s sometimes true, undereating is often the hidden culprit.

Is It Actually Undereating?

The Marathon Handbook highlights that many signs of “overtraining” are actually signs of not eating enough to support your training load. Especially in hot weather, when appetite can be suppressed, and sweat losses are high.

Low energy availability leads to:

Impaired glycogen storage = sluggish legs
Poor recovery and muscle breakdown
Hormonal disruption (especially in female athletes)
Increased injury risk (bone stress injuries, tendinopathies)
Elevated cortisol and disrupted sleep
Compromised immune function

Summer Heat Increases Your Calorie Needs

When you run in the heat, your body’s calorie needs go up, not down.

Even if you aren’t “hungry” after a sweaty run, your body still needs:

✅ Fuel to replenish glycogen

✅ Protein to rebuild muscles

✅ Electrolytes and fluids to restore hydration status

And if you’re trying to lose weight while training hard?

Be very cautious with aggressive calorie deficits in summer.

The combination of high mileage, heat stress, and under-eating is a recipe for burnout and injury.

How To Know If You’re Undereating vs. Overtraining

Ask yourself:

Am I eating enough to match my training load and daily life stress?
Am I avoiding carbs or restricting calories aggressively?
Is my fatigue improving with more sleep and fueling, or only with full rest days?
Have I lost my period (for female athletes), lost noticeable weight unintentionally, or am I constantly thinking about food?

If fatigue improves when you increase calorie intake and hydration, it’s likely under-eating. If it persists despite eating adequately and getting good sleep, it might be true overtraining requiring rest and a review of your training plan.

Tips To Avoid Both This Summer

Fuel your runs. Even short easy runs over 45-60 minutes in heat may benefit from electrolytes or a small carb boost.
Eat enough carbs daily. Aim for at least 5-7g per kg body weight for moderate training days; 7-10g/kg for heavy training days (ACSM recommendations).
Hydrate adequately. Replace sweat losses with electrolyte-rich fluids, not just water.
Listen to your body. Adjust intensity, mileage, and fueling to match the heat.
Prioritize recovery. Sleep, active recovery, and stress management are essential training tools.

If you’re feeling stuck with fatigue, plateaued performance, or injuries creeping in, it’s time to look at both your training and your nutrition strategy.

I’m here to help you train smarter, fuel better, and run stronger all summer long.

Let’s chase your version of awesome.

Happy running

Dayna - your fav. Exercise Physiologist & Run Coach