Why Do I Crash During Workouts?

  • By Tom Coughlin

Published: Wednesday, August 26th, 2026

Quick answer

If you regularly crash during workouts, the problem isn’t necessarily your pre-workout wearing off.

A sudden drop in energy can come from low carbohydrate availability, poor hydration, inappropriate caffeine use, starting too hard, inadequate sleep or simply carrying too much fatigue into the session.

For longer or harder training, getting the basics right usually makes the biggest difference: arrive fuelled, use carbohydrate when the session demands it, replace fluid and electrolytes, and use caffeine strategically rather than relying on increasingly large doses.

MOVE Endurance and Carb Booster can help cover several of these areas within a properly planned training strategy.

Complete Endurance Setup

Why do you suddenly lose energy during a workout?

Most athletes know the feeling.

The session starts well. You feel switched on, the first few sets or kilometres feel good, and then suddenly everything becomes harder.

Your legs feel heavy. Motivation drops. The weights feel heavier or the running pace becomes harder to maintain.

It’s tempting to blame this on your pre-workout “wearing off”, but that’s often too simplistic.

Performance during training depends on several systems working together. Your muscles need fuel. Your cardiovascular system needs to deliver oxygen. Your brain has to tolerate increasing effort. Fluid and electrolyte balance needs to be maintained, and you need to arrive at the session sufficiently recovered in the first place.

When one or more of those areas starts to fall behind, it can feel like hitting a switch.

The first step is working out what is actually causing the crash.

Is a workout crash caused by low blood sugar?

Sometimes, but not always.

Blood glucose is an important fuel during exercise, particularly as intensity increases. Your body also stores carbohydrate as glycogen inside the muscles and liver, which can be broken down and used during training.

If carbohydrate availability is low, maintaining high-intensity exercise becomes progressively harder.

This is especially relevant if you:

- Train after several hours without eating

- Have eaten very little carbohydrate that day

- Are dieting aggressively

- Complete multiple sessions in the same day

- Start a long endurance session poorly fuelled

- Regularly train for more than 60–90 minutes

Sports nutrition guidelines consistently show that carbohydrate availability supports sustained moderate-to-high-intensity exercise performance.[1,2]

That doesn’t mean every moment of low energy is clinical hypoglycaemia.

In healthy athletes, what feels like a “blood sugar crash” is often a broader reduction in carbohydrate availability alongside increasing muscular and central fatigue.

The practical solution is the same: make sure the session is actually fuelled for the work you’re asking your body to do.

Should you eat carbohydrates before training?

For most hard sessions, yes.

Carbohydrate before exercise helps increase carbohydrate availability and supports the ability to sustain training intensity.

How much you need depends on the session.

A short easy workout after a normal day of eating doesn’t require a huge carbohydrate feed.

A hard interval session, high-volume gym workout or long endurance session is different.

If I’ve got a key long run or demanding interval session, I’m much more deliberate with carbohydrate beforehand. I know from experience that caffeine can make me feel ready to train, but it can’t provide the fuel needed to actually sustain the work.

That distinction is important.

You can feel highly stimulated and still be underfuelled.

Can carbohydrate during training stop you crashing?

During longer exercise, carbohydrate intake can help maintain blood glucose, preserve carbohydrate availability and sustain performance.[1, 2, 3]

This becomes increasingly useful once exercise extends beyond around 60–90 minutes, although hard sessions can benefit earlier depending on the athlete and their pre-exercise nutrition.

MOVE Carb Booster provides 30 g of highly branched cyclic dextrin per serving.

Highly branched cyclic dextrin is an advanced carbohydrate with a high molecular weight and low osmolality. Research shows that it empties from the stomach quickly and is well tolerated during exercise.[4,5]

That makes it useful when you need fuel without creating an overly sweet or heavy drink.

One serving provides a straightforward 30 g carbohydrate unit. For longer sessions, it can be combined with additional Carb Booster, gels, chews or food depending on the athlete’s planned carbohydrate target.

The important thing is to start fuelling before you feel completely empty.

Waiting until you’ve already crashed makes it much harder to recover the quality of the session.
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Can caffeine cause an energy crash?

Caffeine itself doesn’t usually create the dramatic blood sugar crash people sometimes blame it for.

What can happen is that caffeine temporarily makes you feel more alert and reduces your perception of effort, while the underlying causes of fatigue continue developing.

Caffeine works primarily by blocking adenosine receptors in the central nervous system. This improves alertness and reduces perceived effort, which is why it is so effective for exercise performance.[6]

But caffeine doesn’t replace carbohydrate, fluid or recovery.

If you take a large caffeine dose before a poorly fuelled session, you can feel fantastic for the first part of the workout while glycogen availability, dehydration or accumulated fatigue gradually catches up with you.

Once the session becomes harder, it can feel as though the caffeine has suddenly stopped working.

In reality, the underlying physiological cost of the workout has become greater than the stimulant can mask.

Is taking more caffeine the answer?

Usually not.

One of the easiest mistakes to make is responding to flat training by gradually increasing the amount of caffeine you take.

A scoop becomes a larger scoop. Then coffee gets added. Then a caffeinated gel goes on top.

At some point, you’re no longer solving the problem.

Higher caffeine intakes increase the risk of anxiety, gastrointestinal symptoms, shakiness, sleep disruption and other side effects.[6,7]

MOVE Strength contains 228 mg caffeine, while MOVE Endurance uses a more controlled 150 mg dose.

That difference matters.

For a heavy strength session, I’m happy using a more concentrated caffeine dose around one defined workout.

For a long endurance session, I’d rather start with 150 mg and retain the option to use caffeine later when fatigue becomes more significant.

The aim is strategic caffeine use, not maximum caffeine use.

STRENGTH Formula

ENDURANCE Formula
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Can poor hydration make you crash?

Absolutely.

As sweat losses increase, plasma volume falls and the cardiovascular system has to work harder to maintain blood flow.

Heart rate can rise, perceived effort increases and the same pace or power output becomes more difficult to sustain.[8]

This can easily feel like an energy crash.

MOVE Endurance provides 495 mg sodium, 726 mg chloride and 118 mg potassium per serving.

Sodium and chloride are the main electrolytes lost through sweat, while potassium contributes to fluid balance and normal neuromuscular function.

That makes MOVE Endurance particularly useful for longer sessions, hot-weather training and athletes with higher sweat rates.

The amount of fluid and sodium you need is still individual.

Some athletes barely sweat during an indoor strength session. Others can lose more than a litre of fluid per hour during running or conditioning.

In practice, I look at the athlete, the environment and the session rather than assuming everybody needs the same hydration target.

Could you simply be starting too hard?

Yes, and this is probably one of the least exciting but most common explanations.

Starting a session harder than you can realistically sustain accelerates carbohydrate use and increases metabolic stress.

In endurance training, this might mean running the opening kilometres significantly faster than planned.

In the gym, it could mean turning every warm-up set into work, taking very short rest periods or adding unnecessary volume early in the session.

You can feel brilliant for 20 minutes and still set yourself up for a poor second half.

I’ve definitely learned this the hard way during long-distance running.

Feeling fresh at the start of a four-hour run doesn’t mean I should run the first hour like it’s a 10 km race.

The same principle applies to fuelling and stimulants: don’t let feeling good early convince you that the physiological cost has disappeared.

Is poor recovery causing the crash?

Sometimes the problem started long before you walked into the gym.

Sleep loss, accumulated training load, inadequate energy intake and insufficient recovery between sessions all reduce training readiness.

No pre-workout can completely override that.

Sleep is particularly important.

Restricted sleep negatively affects physical performance, cognitive function, reaction time and perceived effort.[9] At the same time, using large amounts of caffeine later in the day to compensate for tiredness can further disrupt subsequent sleep.[10]

That creates an obvious cycle:

Poor sleep leads to fatigue.

Fatigue leads to more caffeine.

Late caffeine leads to worse sleep.

Then the athlete needs even more stimulation the following day.

MOVE Decaf can be useful here because it allows athletes to maintain their pre-training routine and support focus without adding another caffeine dose.

But the bigger solution is still addressing the recovery problem.

DECAF Formula
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How can you tell what is causing your workout crash?

Look at when the problem happens.

 

You crash early in the workout

Think about:

- Poor sleep

- Inadequate pre-training food

- Training too soon after waking

- Excessive fatigue

- Starting the session too aggressively

 

You crash after 60–90 minutes

Think about:

- Carbohydrate availability

- Fluid intake

- Electrolyte losses

- Session pacing

- Whether you need during-exercise fuel

 

You feel great initially and then suddenly feel flat

Think about:

- Over-reliance on a large caffeine dose

- Starting too hard

- Training with inadequate carbohydrate

- Accumulated fatigue being temporarily masked by stimulation

 

You crash during hot sessions

Think about:

- Sweat rate

- Fluid availability

- Sodium losses

- Heat exposure

- Whether your pace needs adjusting

 

The timing of the crash often gives you a much better clue than simply assuming you need a stronger pre-workout.

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What should you eat before training to avoid crashing?

For a demanding workout, aim to include carbohydrate in the pre-training meal or snack.

Good options include:

- Porridge with fruit

- Toast with jam or honey

- Cereal and milk

- Rice or pasta with a meal

- A banana and yoghurt

- A carbohydrate-based sports drink when solid food isn’t practical

The closer you get to training, the simpler and easier to digest the food should generally become.

Protein can also be included, particularly before resistance training, but carbohydrate is the main nutrient to think about when the problem is maintaining high-intensity energy availability.

If you regularly train very early in the morning, even a relatively small amount of easily digested carbohydrate can be more useful than starting completely fasted.

What MOVE combination works for longer sessions?

For a longer endurance or hybrid session, MOVE Endurance plus Carb Booster gives you a useful foundation.
MOVE Endurance provides:
- 150 mg caffeine
- 1.5 g taurine
- 900 mg blackcurrant extract
- 495 mg sodium
- 726 mg chloride
- 118 mg potassium
- L-arginine and vitamin C for nitric-oxide and oxygen-delivery support
Carb Booster adds 30 g highly branched cyclic dextrin.
Together, that gives you stimulation, fatigue-resistance support, hydration and carbohydrate in one practical drink.
For multi-hour sessions, it should still form part of a larger fuelling strategy rather than being treated as everything you need.
That could mean additional carbohydrate, fluid and sodium depending on the athlete and the session.

SHOP HERE
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Tom's Take

When someone tells me they “crash” during training, my first thought isn’t that they need a stronger pre-workout.

I want to know what they ate, when they ate it, how long they’re training for, how much they’re drinking, how they slept and what the first half of the session looked like.

I use exactly the same process with my own training.

During long runs, I know I can’t caffeine my way out of poor fuelling. If I under-eat carbohydrate or don’t keep on top of fluids, that will catch up with me eventually.

And strength training isn’t that different. If I’ve had a busy day, eaten badly and slept for five hours, 228 mg of caffeine can help me feel more switched on, but it doesn’t suddenly make me fully recovered.

That’s where I think people sometimes get pre-workout wrong.

It should enhance a good setup, not hide a bad one.

Use MOVE Strength when you need focused stimulation for a demanding strength session. Use Endurance when hydration, sustained effort and fatigue resistance matter. Add Carb Booster when carbohydrate availability becomes part of the problem.

But if you’re crashing every single workout, look beyond the scoop.
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
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Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
Complete Endurance Setup
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Complete Endurance Setup
Complete Endurance Setup

Complete Endurance Setup

£49.98

Combine MOVE Endurance for hydration, stamina and energy with Carb Booster for clean, sustained fuel to power longer, harder sessions. Available in 3 flavours.
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