What is it? What does it mean? And do you need to do it?
Let's break it down simply.
Say you're someone who runs twice per week and lifts three times per week. Let's call each training session three units of training. That's five sessions per week, or 15 units of training.
As the weeks go on, you train harder and harder. That 15 units gradually becomes 18... then 20 units of training. Let's say your physiological system can recover from 20 units. That is your maximal recoverable volume (MRV).
Now, if you sleep well and eat well, that 20 units might creep up to 21 or 22. But for simplicity, we'll say your MRV is 20.
If you train at 21 units for one week, you are technically above MRV - you are now overreaching.
If you train at 22 or 23 units, you are really overreaching.
What makes this functional is that it is planned and immediately followed by a period of reduced training.
So let's say you train at 22 units for one week. After that, you drop training down to, say, five units per week for roughly the same duration you overreached for. That reduction might come via a deload, reduced intensity, reduced volume, or even time completely off.
That's the structure.
How do we know we're overreached?
First: objectively.
Performance tanks - not a small drop, a large one.
You can usually do 15 pull-ups in your first set. You get 9. Then 6. You can usually run a 5K in 20 minutes. It now takes 26 minutes. That's the objective signal.
Second: subjectively.
Rate of perceived exertion goes through the roof.
This is driven by increased inhibitory signalling - neurotransmitters like GABA in the brain and glycine in the spinal cord hyperpolarize neuronal cells. In layman's terms, the nervous system becomes less excitable. Neurons are less likely to fire, and even when they do, everything feels harder.
Bar velocity tanks.
Every rep feels grindy.
Same load, same pace - massively higher effort.
Motivation also drops. Catecholamines like dopamine become depleted. Even if you're normally highly driven, you suddenly don't want to train. You don't want to push. That's not weakness - that's your nervous system actively shutting you down.
So subjectively:
- RPE skyrockets
- Desire to train drops
- Bar speed decreases
- Mood disturbances increase
Objectively:
- Performance declines consistently over time
- Not a one-off bad session - a pattern
Why would we ever do this?
Because there is solid literature showing that pushing systems beyond what they can currently tolerate, especially at advanced levels, is often the only way to continue progressing.
For elite athletes, functional overreaching can be a powerful tool.
For everyday lifters and runners, it's not mandatory - but understanding it is crucial.
Knowing where your limits are - where your MRV sits - helps you avoid accidentally drifting into non-functional overreaching or outright overtraining.
When functional overreaching is followed by a proper reduction in training, good sleep, and good nutrition, you often return to training with a higher baseline.
That 15 pull-ups becomes 16 or 17. That 20-minute 5K becomes 19:30.
On a deeper level, we even see molecular adaptations - including satellite cell proliferation, where supportive stem-like cells donate nuclei to muscle fibers. More nuclei means greater capacity for protein synthesis over time.
So, do you need to do it?
No - normal progressive overload will work for most people.
But functional overreaching is the most potent adaptation-driving tool we have when used intelligently. It ensures effort isn't the limiting factor. It ensures no gains are left on the table.
And sometimes - especially once you're experienced - fully sending it, deliberately, with a plan in place to recover afterward, is the fastest way to find your true ceiling.
Sometimes you do need to fuck around and find out - as long as you know exactly why you're doing it.