Share with another athlete
Why Do You Feel Angry, Flat or Nauseous After Training or Racing?
The Science Behind the Post-Exercise Crash
You've just crossed the finish line.
Or completed your hardest training session of the week.
You should feel proud. Relieved. Happy.
Instead, you're exhausted.
You snap at your partner.
Burst into tears over something small.
Feel strangely empty.
Or perhaps you feel so nauseous that eating is the last thing you want.
If you've ever experienced this, you're not imagining it.
These post-exercise crashes are surprisingly common and they're rooted in physiology.
They're often the result of several systems all trying to recover at once:
- depleted carbohydrate stores
- changes in brain chemistry
- activation of your stress response
- reduced blood flow to the gut during exercise
- dehydration and electrolyte losses
- inflammation from muscle damage
- and, in some athletes, chronic low energy availability (RED-S)
Understanding what's happening can make recovery easier—and may help prevent the same cycle happening after every hard session.
Your Brain Is Running Low on Fuel
Most people think carbohydrates are just for muscles.
In reality, your brain is one of the body's biggest consumers of glucose.
During prolonged or high-intensity exercise, muscle glycogen stores become depleted while the liver continually releases glucose to maintain blood sugar and supply the brain.
As exercise continues, liver glycogen also begins to fall.
If carbohydrate intake before and during exercise has been inadequate, blood glucose can become more difficult to maintain.
When this happens, athletes may notice:
- irritability
- poor concentration
- feeling overwhelmed
- emotional sensitivity
- difficulty making decisions
This is why post-race "hanger" can feel much more intense than everyday hunger.
Your brain is asking for fuel as much as your muscles are.
Your Stress Hormones Suddenly Switch Off
During racing, your body is flooded with hormones designed to keep you moving.
These include:
- adrenaline
- noradrenaline
- dopamine
- cortisol
- endorphins
Together they increase alertness, reduce pain perception, mobilise carbohydrate stores and help you sustain performance.
Once you stop exercising, these hormones rapidly decline.
The nervous system shifts from a highly activated "fight or flight" state towards recovery.
That sudden transition is one reason athletes often report feeling:
- emotionally flat
- tearful
- unusually irritable
- unmotivated
- disconnected from what they've just achieved
Some researchers also suggest that prolonged exercise temporarily alters neurotransmitters such as serotonin and dopamine, which may contribute to mood changes immediately afterwards.
Exercise Is Also An Inflammatory Stress
Long or intense exercise creates microscopic muscle damage.
This is normal and is part of the adaptation process.
However, repairing that damage requires energy.
Following prolonged endurance events, inflammatory cytokines such as interleukin-6 (IL-6) increase substantially.
Although IL-6 helps regulate metabolism during exercise, high post-exercise levels are also associated with:
- fatigue
- reduced appetite
- feeling unwell
- low mood
- "brain fog"
In other words, your body is recovering from controlled physical trauma.
Feeling flat afterwards is not simply psychological.
Why Do You Feel Nauseous After Hard Exercise?
Many athletes struggle to eat immediately after racing.
This is frustrating because it's exactly when recovery nutrition matters most.
Several physiological changes contribute.
1. Blood is diverted away from your digestive system
During intense exercise, up to 80% of blood flow can be redirected towards working muscles, the heart, lungs and skin for cooling.
That means the stomach and intestines temporarily receive much less blood.
Digestion slows.
Stomach emptying becomes delayed.
Food simply doesn't feel appealing.
2. Your nervous system is still in "fight or flight"
Adrenaline suppresses digestion.
Even once you've stopped exercising, it can take time before the parasympathetic ("rest and digest") nervous system takes over.
Until then, nausea, bloating and loss of appetite are common.
3. Heat and dehydration make symptoms worse
If you've lost significant sweat during training or racing, dehydration further reduces blood volume.
This means even less blood is available for the digestive tract.
Hot races consistently produce higher rates of nausea than cooler events.
Electrolyte losses—particularly sodium—may also contribute to dizziness and feelings of sickness.
4. The Gut Barrier Becomes More Permeable
During prolonged endurance exercise, reduced gut blood flow can temporarily increase intestinal permeability—sometimes referred to as a "leaky gut" response.
This allows bacterial components, such as lipopolysaccharides (LPS), to enter the bloodstream more easily, triggering an inflammatory response.
This is thought to contribute to:
- nausea
- stomach cramps
- diarrhoea
- loss of appetite
- feeling generally unwell after racing
The harder and longer the event—and the hotter the conditions—the more likely these symptoms become.
5. Low Blood Glucose Can Contribute
If carbohydrate intake has been insufficient before or during exercise, blood glucose may fall after finishing.
Low blood glucose can produce symptoms including:
- shakiness
- dizziness
- sweating
- nausea
- headaches
- irritability
Another reason why replacing carbohydrate soon after exercise is so important.
When Under-Fuelling Makes Everything Worse
For some athletes, these symptoms aren't just the result of one hard race.
They're amplified because the body has been under-fuelled for weeks or months.
Low Energy Availability—the underlying cause of Relative Energy Deficiency in Sport (RED-S)—occurs when there isn't enough dietary energy left to support normal physiological function after accounting for exercise.
The consequences extend far beyond performance.
RED-S can affect:
- hormone production
- bone health
- immune function
- cardiovascular health
- recovery
- mood
- concentration
- menstrual function
- injury risk
If your baseline energy availability is already low, one hard session can tip the body even further into deficit.
Recovery becomes slower.
Mood becomes lower.
Fatigue lasts longer.
Why Recovery Nutrition Matters Even When You Don't Feel Hungry
One of the biggest mistakes athletes make is waiting until appetite returns.
Unfortunately, hunger is not always a reliable guide immediately after exercise.
You may not feel like eating.
Your body still needs:
✅ Carbohydrate to replenish glycogen.
✅ Protein to stimulate muscle repair.
✅ Fluids to replace sweat losses.
✅ Electrolytes to support rehydration and normal muscle and nerve function.
The goal isn't necessarily to eat a large meal immediately.
The goal is to start recovery.
Even a small amount of carbohydrate soon after exercise can begin replenishing glycogen stores and may make it easier to eat a larger meal later.
Why RED-Scue Exists
RED-Scue was created from lived experience.
I wanted something I could manage when a full meal felt impossible after training or racing.
Each RED-Scue bar provides approximately 38 g of carbohydrate, helping athletes begin replacing the fuel they've used during exercise.
They're built around whole-food carbohydrate sources, including cassava and plantain, rather than relying primarily on oats or syrups.
Plantain naturally contains potassium, a mineral involved in normal muscle function and fluid balance, while cassava provides an easily digestible source of carbohydrate.
Rather than replacing a proper recovery meal, RED-Scue is designed to bridge the gap—to provide that crucial first bite when appetite is low.
A practical recovery approach might look like this:
- Within 30–60 minutes: one RED-Scue bar and fluids (plus electrolytes if you've had heavy sweat losses).
- Over the next 1–2 hours: follow with a balanced meal containing carbohydrate, protein, colourful fruit or vegetables, and fluids.
Sometimes recovery doesn't begin with a plate of food.
Sometimes it begins with something you can actually manage to eat.
Final Thoughts
If you've ever finished training or racing and wondered:
"Why am I so emotional?"
"Why do I feel completely flat?"
"Why can't I face eating?"
There is a physiological explanation.
Your brain, nervous system, muscles and digestive system are all responding to the stress of exercise.
For most athletes, these feelings improve as energy stores are restored and the body recovers.
However, if emotional crashes, persistent nausea, poor recovery or overwhelming fatigue become a regular pattern, it may be worth looking beyond the race itself and considering whether your day-to-day fuelling is meeting the demands of your training.
Recovery doesn't start when you finally feel hungry.
It starts when you begin replacing the energy your body has worked so hard to use.
