Mental fatigue does not show up the way physical fatigue does. You will not see sore muscles or a slower sprint. Instead, it creeps in quietly. Reaction time slows. Decisions become less clean. Coordination slips. Focus fades long before the body does.

You cannot rely on what you see or on what an athlete says they feel. Mental fatigue must be measured objectively. That is where Soma comes in.

Soma gives you three core tools that reveal exactly how the brain is coping with training load:

These tools give you a complete picture of cognitive load, fatigue, and adaptation across a training block.

Cognitive load is the mental effort required to complete a task. It behaves just like physical load:

The goal is not to avoid mental fatigue. The goal is to track it, manage it, and use it. Without data, you are guessing. You might underload an athlete and see zero improvement. Or overload them and accidentally break their cognitive control.

Objective data removes the guesswork. It tells you:

• When the brain is fresh

• When the brain is fatigued

• When the brain has adapted

• When to push forward

• When to pull back

Once you can measure mental fatigue, you can coach it with precision. And once you can coach it, performance begins to change in a predictable and measurable way.

The PVT-B is a simple reaction test designed to measure mental fatigue with very high sensitivity. There is no strategy and nothing to hide behind. The athlete simply reacts as fast and accurately as possible, which makes even small drops in focus show up in the data.

At the start of the test, reaction time is fast, accuracy holds, and responses are consistent.

As fatigue appears, three things happen:

→ Reaction time slows

→ Lapses increase

→ Variation rises

These shifts reveal exactly how well the brain is coping with training load.

The PVT-B gives you a clear picture of readiness, fatigue, and recovery. It shows when the brain is sharp, when it is starting to tire, and how much strain a session actually created.

Simple vigilance tasks reveal fatigue faster than anything else, and the PVT-B works so well because it is intentionally simple. There is nothing complex to learn and nothing for the athlete to compensate with. They just react, which means that when the brain begins to tire, the decline in performance shows up immediately and clearly.

The most important metric to watch is lapse count. A lapse is any reaction slower than 355 milliseconds, and even a small rise in lapses is one of the strongest and most reliable signs that cognitive fatigue has appeared. Lapses increase the moment the brain starts losing focus or struggling to stay alert, which makes them far more sensitive than reaction time alone.

Reaction time often shifts only slightly when fatigue sets in, but lapses expose the real breakdown. This is why the PVT-B is so effective. Even small drops in cognitive control show up instantly in the data, giving you a clean and honest picture of mental fatigue.

What Each Metric Means

When you analyze PVT-B data, there are three metrics that really matter, and each one tells you something different about how the brain is coping under load.

Reaction time shows how fast the athlete responds, but it should never be the only number you look at. Reaction time often changes only a little when fatigue first appears, so it is useful but not sensitive enough on its own.

Variation shows how consistent the athlete is from one response to the next. When variation begins to rise, it means focus is slipping and the brain is finding it harder to maintain control. Variation is one of the earliest signs that mental fatigue is building.

Lapses show the moments where the brain fully disconnects or slows down. A lapse is any response slower than 355 milliseconds, and even a small increase in lapses is the strongest signal that cognitive fatigue has arrived.

Viewed together, these three metrics give you a clear and honest picture of how well the athlete is maintaining attention, control, and consistency as fatigue builds.

Healthy fatigue response:

→ RT slightly slower

→ Variation slightly higher

→ 1 to 5 lapses

This means the training load was high enough to create adaptation, but not so high that quality collapsed.

Unhealthy fatigue response:

→ More than 5 lapses

→ Large increase in variation

→ RT + variation + accuracy breaking down together

This means the athlete was overloaded and needs recovery before progressing.

Recovery rule:

Pre-session lapses must return to 0 to 3 before the next session.

Healthy

Unhealthy

Use the PVT-B before and after training sessions to see exactly how the load affected the brain.

Pre-session PVT-B

Shows the athlete’s readiness and how well they recovered from the previous session. If lapses are already high, the brain is not fresh.

Post-session PVT-B

Shows how much cognitive fatigue the session created. This is where variation and lapse count reveal whether the load was high enough to drive adaptation.

The goal is simple

Mild fatigue after the session.

Full recovery before the next one, with lapses returning to between 0 and 3.

The PVT-B is the most reliable way to manage cognitive load, monitor strain, and track mental freshness across a training block.

How to Know When to Increase Load

When reaction time, variation, and lapses all flatten out across multiple sessions, the athlete has adapted to the current training load.

Flat PVT-B data means the brain is no longer stressed by the session.

This is normal in the final week of a training block.

It simply means the athlete has absorbed the load and the session is no longer challenging enough to create meaningful fatigue.

Here is an example of what a flattening lapse pattern can look like over 12 sessions:

The PVT-B is one of the most reliable ways to detect mental fatigue. It strips away complexity and focuses on the three clearest signs that the brain is starting to tire: reaction time, variation, and lapses. Because the task is simple, athletes cannot hide fatigue. When the brain slows down, the data shows it immediately.

The PVT-B tells you:

If the training load was high enough

Small rises in variation and a few lapses confirm the session created meaningful cognitive stress.

If the load was too high

More than five lapses or sustained high variation shows the athlete exceeded their capacity.

If recovery is complete

Pre-session lapses returning to 0–3 means the brain is reset and ready for the next load.

When to progress the plan

When reaction time, variation, and lapses flatten for several sessions, the athlete has adapted and needs more challenge.

The PVT-B matters because it gives you a simple, objective window into the athlete’s cognitive state. It shows how their brain responds to training, how quickly they fatigue, and whether they are adapting. With this information, you can calibrate load, increase resilience, and prevent overtraining. It turns mental fatigue from a guess into a measurable signal you can coach with.

Mistake 1: Only looking at reaction time

Reaction time barely changes when real fatigue appears, so it cannot be your only metric.

Mistake 2: Ignoring variation

Variation is often the first sign that cognitive control is slipping.

Mistake 3: Overloading every session

Progress requires fatigue, but not burnout. Too much load destroys adaptation.

Mistake 4: Reading data without context

Always compare the numbers to the athlete’s normal baseline before drawing conclusions.

Mistake 5: Expecting stable data during off-season

Early chaos followed by later stability is normal. This is how adaptation works.

The Psychomotor Fatigue Threshold Test identifies the point where cognitive performance begins to decline during exercise. It is one of the most effective tools for measuring cognitive endurance and detecting when the brain starts to break down under physical stress.

As physical intensity rises, the brain sharpens for a while. Reaction time gets faster, accuracy improves, and variation drops. This is the brain’s peak zone. The PFTT shows you when that peak ends and the decline begins.

When reaction time slows and accuracy drops, the threshold has been crossed. Over time, the goal is to push that point further out. If the threshold appears later in the session, the athlete’s mental endurance has improved.

The PFTT uses a simple three-choice reaction task:

• Tap right for red

• Tap left for green

• Do not tap for yellow

That is the entire task.

It looks simple, but it is extremely sensitive to fatigue. As physical load increases, even small drops in control show up clearly in the data. Because the rules are easy and the response is fast, you get a clean signal of how the brain is coping with rising physical stress.

A simple task is the most sensitive way to see when the brain begins to fatigue. Complex tasks allow athletes to compensate and hide mistakes. Simple tasks do not. They expose real cognitive decline because there is nothing to hide behind.

The PFTT uses three signals to reveal the breaking point:

→ Reaction time slowing

→ Accuracy dropping

→ Variation rising

When these shift together, the threshold has been reached. That is the moment cognitive performance begins to decline under physical stress.

The threshold is the moment the brain stops improving and begins to decline. It is where cognitive fatigue appears.

Use this simple rule:

The threshold has been reached when:

→ Reaction time rises for one to two consecutive readings

→ Accuracy begins to drop

→ Variation starts to rise

These changes together show that the brain is losing control and moving out of its peak zone.

Once the threshold appears, you can choose to:

→ Push further to extend fatigue tolerance

or

→ Stop the session to protect decision quality

Both options are correct. The right one depends on your training goal.

There are three simple ways to use the PFTT. Choose the option that fits your training session.

Option 1: Before, Mid, and After Training

• PFTT before the session

• PFTT halfway through

• PFTT after the session

This shows how cognitive fatigue builds from start to finish. It reveals when the brain starts to slow down.

Option 2: Between Physical Sets

Run a PFTT after each block of physical training.

This shows when the brain begins losing speed, accuracy, or control as fatigue accumulates.

Option 3: Combined During Training

Physical work → PFTT → Cognitive task → Repeat

This shows how the threshold shifts when physical and cognitive load are combined. It reveals how well the athlete can recover and refocus as demands change.

Every PFTT follows the same three phases:

Build Phase

Reaction time improves.

Accuracy stabilises.

Variation drops.

The brain is warming up.

Peak Phase

Reaction time is at its fastest.

Variation is at its lowest.

Decision-making is clean and stable.

This is the athlete’s peak zone.

Threshold Phase

Reaction time slows.

Accuracy drops.

Variation rises.

Fatigue has arrived.

This curve shows how long the athlete can stay sharp before cognitive decline begins.

The goal is to push the threshold further out over time.

Signs of progress include:

→ Threshold appears later in the session

→ Reaction time stays sharp under more fatigue

→ Accuracy remains stable for longer

→ Variation stays low as load increases

A longer peak and a delayed drop indicate improved cognitive endurance.

Monitor PFTT reaction time, accuracy, and variation across the training block. You want the athlete to sustain sharp performance for longer before decline begins.

If reaction time dips early, variation rises quickly, or accuracy falls sharply, the athlete has a low cognitive fatigue threshold.

If these stay stable for longer, their endurance is stronger.

If you can measure the breaking point, you can train it.

The PFTT shows whether an athlete:

• Fatigues too quickly

• Loses cognitive control under physical stress

• Has low cognitive resilience

• Can maintain decision quality as fatigue builds

• Is adapting to training over weeks

When you can measure the threshold, you can move it.

When you can move it, performance changes.

The Rating of Mental Fatigue (RMF) scale captures how mentally tired the athlete feels after each task. It connects subjective feedback with objective data, showing whether perception and actual performance match. The RMF scale is built into Soma and links automatically to each task. It is best used to confirm how mental fatigue feels compared to what the data shows.

Start with the basics. Track lapse count first using the PVT-B, because it is the clearest and most sensitive marker of mental fatigue. Then use the PFTT to find the exact moment the brain begins to decline under physical stress, and add the RMF scale to compare how the athlete feels with what the data shows.

When you combine cognitive data with physical data, you get the full picture. You can see whether the athlete is adapting, carrying fatigue, or ready for more load. Mental fatigue is not something to avoid. It is a signal. It is feedback. When you measure it and understand it, you can use it to guide progression with precision.

Soma gives you that clarity. It shows you when to push, when to pull back, and when the brain is in the right state to adapt.

→ Finding the Brain’s Breaking Point

Learn how to identify the psychomotor fatigue threshold, read the rise in reaction time, and track cognitive decline during exercise.

→ How to Use the PVT-B Task to Measure Mental Fatigue

Understand lapses, variation, reaction time, and how to judge load, recovery, and adaptation with the simplest vigilance test.