Why Do I Crash Mid-Workout?
Why Do I Crash Mid-Workout? 5 Causes and How to Fix Them
By Dominic Paris, strength and conditioning coach
I’ve worked corners for world champion boxers, and I’ve trained executives who could barely find an hour between meetings. Different worlds, same complaint, almost word for word:
“I was strong through the first part, then I just fell apart.”
The fighter says it about the fourth round. The executive says it about the last 15 minutes of a lunchtime session. Both assume they ran out of toughness or conditioning.
Almost every time, they’re wrong. If you crash mid-workout at about the same point each session, the cause is usually a fuel problem. And a fuel problem is far easier to fix than a fitness problem.
Why the crash is not a conditioning problem
Your body runs on a few specific resources: stored carbohydrate, blood sugar, fluid and sodium. When training demands more of one than you have available, performance drops. Often sharply, in a window you can almost set your watch to.
Heavy legs at minute 40. A power drop in round four. Hitting the wall two hours into a long ride.
That isn’t your will breaking. It’s a resource running short.
This matters because you can’t pull harder on “toughness” on demand. You can change what you eat before training, what you take in during it, and how much you drink. But first you need to know which resource is running out.
I group the causes into five Fade Types. Each has its own timing, its own feel and its own fix.
1. Glucose Fade: the early energy crash
When it hits: in the first 10 to 30 minutes, sometimes before you’ve broken a real sweat.
What it feels like: shaky, foggy, suddenly flat.
Why it happens: this is a blood sugar problem, not an empty tank. A big hit of refined carbohydrate with nothing to slow it down spikes your blood sugar. Your body releases insulin to bring it down. Add the glucose your muscles pull in once you start moving, and blood sugar can overshoot downward.
First fix: when you eat more than about an hour before training, pair your carbohydrate with some protein and a little fat. Oatmeal alone can spike and dip. Oatmeal with a scoop of protein and a spoon of nut butter digests more evenly. Inside the last 30 to 60 minutes, flip it: keep it small, simple and low in fiber and fat.
2. Glycogen Fade: hitting the wall
When it hits: gradually, somewhere past 45 to 60 minutes of hard work.
What it feels like: a steady loss of power or pace. Heavy legs, slower hands, no single crash.
Why it happens: your muscles and liver store carbohydrate as glycogen, and the tank is smaller than most people think. A trained adult typically holds enough for roughly 90 to 120 minutes of continuous moderate-to-hard effort. Less if the intensity is high, or if you started with the tank half empty from yesterday. Lifting counts too. A long, high-volume strength session can drain it.
First fix: match your fueling to the session. A 40-minute lifting session rarely needs fuel during the workout. Long, hard sessions do. And if you train again within 24 hours, eat a meal with carbohydrate in the hour or two after training, when the tank refills fastest.
3. Hydration Fade: when everything feels harder than it should
When it hits: it tracks heat and how much you drank that day more than the clock.
What it feels like: effort feels out of proportion. Heart rate runs high for the work you’re doing.
Why it happens: sweat is pulled largely from your blood plasma. Lose enough and your heart has to work harder to deliver the same oxygen. Performance declines once fluid loss reaches roughly 2% of body weight. For a 180-pound athlete, that’s about three to four pounds of sweat, which is easy to lose in a hard hour.
First fix: thirst is a late signal, so get a number. Weigh yourself right before training and again right after. If you dropped more than about 2% of your body weight, drink more during your next session, spaced through the workout. Don’t overdo it, either. Drinking far more plain water than you lose carries its own risks.
4. Electrolyte Fade: heavy, sluggish, sometimes crampy
When it hits: in long or hot sessions, especially if you sweat heavily.
What it feels like: heaviness, sluggishness, sometimes cramping.
Why it happens: sodium helps your nerves signal your muscles and helps your body hold on to the fluid you drink. Heavy sweating can deplete it. I’ll be straight with you on cramping: the science is more complicated than “low sodium equals cramps.” Muscle fatigue plays a real role too.
First fix: check three things. Do you see salt marks on your clothes? Does it happen mainly in sessions past an hour or in heat? Have you been avoiding salt in your diet? Two or more yeses, and you should add a source of sodium around long or hot sessions, such as an electrolyte drink or a salted snack.
5. Under-Fueling Fade: flat in every session
When it hits: across most sessions, whatever you ate beforehand, building over days or weeks.
What it feels like: low energy everywhere, and performance that keeps sliding.
Why it happens: you’re training hard and eating too little to support it. This is common in disciplined people who are leaning out or making weight. No pre-workout meal can outperform a week-long deficit.
First fix: look at your whole week, not one meal. One amateur fighter I coached was sure his conditioning had collapsed. He’d been cutting calories for three weeks on top of a hard camp. We adjusted his weight cut so his intake matched his training, and the problem mostly disappeared within two weeks.
How to find your Fade Type
Ask yourself three questions:
- When does the fade hit? Early, after 45 to 60 minutes, mainly in the heat, or in every session?
- What does it feel like? Shaky and foggy, heavy and fading, breathless, crampy, or just flat?
- What’s your context? What you ate in the last few hours, how long and hard the session is, how much you sweat, and whether you’ve been eating less lately.
More than one type can apply. A long, hot, hard session can hand you two or three at once. Find the main driver and fix that first.
When it’s not a fueling problem
If a symptom is severe or doesn’t go away, stop training. Chest pain, real confusion or fainting is a medical situation, not a nutrition one. See a doctor.
Stop guessing and get the full system
This post gives you the first fix for each Fade Type. My book, Fade-Proof: The Fueling System to End Mid-Workout Crashes, Train Longer, and Perform at Full Power, gives you the complete system:
- The Fade Type worksheet
- A pre-workout meal formula based on your body weight and your time
- The real rules for fueling during a workout
- The few supplements with solid evidence, with doses and timing
- A troubleshooting guide for fixing a fade mid-session
It isn’t your willpower. Find out what it is, and fix it.
Get Fade-Proof
This article is for educational purposes only and is not medical advice. Individual results vary. Consult your doctor before changing your diet, training or supplements.
Frequently asked questions
Place these above the final button. Question-style headings help the post appear for those searches.
Why do I get tired 20 minutes into my workout?
An early crash usually points to blood sugar, not an empty tank. Look at what you ate, or didn’t eat, in the hours before training.
Should I work out on an empty stomach?
Fasted training shifts your fuel mix toward fat during easy movement. For most people doing hard training, though, it lowers the quality of the session itself.
Do I need a sports drink or gel during my workout?
It depends on duration. Short sessions rarely need fuel during the workout. Long, hard or sweaty sessions often do.
Is cramping always caused by low electrolytes?
No. Sodium loss can contribute, especially in long or hot sessions, but muscle fatigue plays a role too.
