Become a Personal Trainer
The All Or Nothing Law Is Simple Enough To Learn In One Sitting
From the FASTER syllabus: this article is taught in full in Level 2 and Level 3 Personal Training, from scratch →
In short: A motor neuron and the muscle fibres it controls make one motor unit. When the nerve fires, every fibre in that unit contracts, or none does. That is the all or nothing law. A whole muscle is many motor units, and not all of them work at once, so the muscle changes how hard it works by changing how many units are active. A thigh motor unit can hold thousands of fibres and a finger's only a few. It is one idea, and it is taught on FASTER's CIMSPA-recognised Level 2 and Level 3 personal training course.
Anatomy is the part of a personal training course that sounds most like school. Names in Latin, diagrams with arrows, and a phrase like "motor unit recruitment" sitting in the unit list.
Here is the short answer to what that phrase means. A nerve and the muscle fibres it controls form a motor unit. When the nerve fires, every fibre in that unit contracts, or none of them does. That is the all or nothing law, and it is the whole idea.
Key Takeaways
- One motor neuron plus its muscle fibres is a motor unit.
- When the nerve fires, all of the unit's fibres activate, or none do.
- A muscle is many motor units, and they do not all switch on together.
What a motor unit is
Muscle fibres connect to the central nervous system through motor neurons. One motor neuron looks after a group of fibres, and that group is the motor unit.
The size of the group changes with the muscle. A thigh muscle can have thousands of fibres answering one motor neuron. In a finger there are only a few. Big, strong muscle, big units. Fine, careful muscle, small units.
The law itself
Fleck and colleagues (1997) called it the all or nothing law. The nerve impulse goes down the neuron, and every fibre in that motor unit is activated. A unit never fires halfway.
One useful detail from the course text: a motor unit is usually made up of one fibre type only, Type I, Type IIa or Type IIb. So the unit is the thing that carries a fibre type into the movement.
So how does a muscle do a soft job and a hard job?
The law applies to a motor unit, and not to the whole muscle. A full muscle is made of numerous motor units, and not all the fibres are activated at the same time when it contracts.
That is the answer to how a muscle can do something gentle one second and something hard the next. It calls on fewer units, or more. The course calls this motor unit recruitment. Once the law is clear, recruitment follows from it in a sentence.
Why the course teaches it, and how
One of the things you learn on our CIMSPA-recognised personal training course is exactly this, as criterion 8.3 of the anatomy unit. It sits next to the nervous system, the muscle actions and the energy systems, and each one is a short idea like this.
The learning is visual and interactive. You see the diagrams, listen to the lessons, read the text, and write or dictate your answers, whichever suits you. Nobody expects a degree. Plenty of people start the course with a job they are leaving and a feeling that science is for other people.
The Level 2 and Level 3 together are £1,500, and PT Manager comes free with them. It opens when you sign up, and day one is for learning on. Real clients unlock once you have qualified and are on the Trainer Register.
FASTER Daily News sends you each day's blog links, the latest on new courses and live opportunities, and updates to PT Manager, free for students. Sign up at /newsletter.
You just read one answer. The course is all of them.
Level 2 and Level 3 Personal Training, from scratch: every answer marked by a real tutor, with free return access for life. The price is on the page, payment plans at checkout, no sales calls.
Also worth a look: PT Manager, free with any FASTER course.
See what the course covers →What every FASTER student gets
Built around you, not around the course
- A real person marks every answerEvery answer is read and marked by a tutor, with written feedback.
- Marked as you goEach teaching point is marked as you answer it, not at the end of the module.
- Dictate instead of typeA microphone on every written answer: say your answer and it types it for you (Chrome, Edge and Safari).
- Listen to the lessonsVoice-overs on the lessons, and the audio to download.
- Built for the way your brain worksShort lessons, one point at a time, marked as you go, with the choice to listen, read, print or speak your answers.
- Streaks that never punish youYou set how many days a week you want to study. Miss a day and your streak pauses; it is never lost.
- Accessible to WCAG AA, with an AAA optionEvery page measured against the WCAG accessibility standard: no faults at level A or AA, with a skip link, screen-reader labels and pages that hold together zoomed to 400%. A high-contrast option takes it to AAA.
- Keep it plainOne switch turns off the extras, the streaks, the badges, the celebrations and the movement, so the site stays plain and calm. Switch them back on whenever you like.
- Bigger text and wider spacingTwo steps of bigger text, and more room between lines, words and letters, on every page.
- Calmer motionOne switch stops animations and videos that play on their own. It is on already if your phone or computer asks for reduced motion.
- A personal video lessonWhen an answer needs real explaining, your marker records a video that lands in your course.
- A note before you sendBefore you send, the page tells you if your answer copies the lesson word for word, so you can put it in your own words.
- The skeleton and muscle labsTap any bone on the skeleton, and see the muscles light up on the model.
- Print the notesPrint the lessons and go old school.
- Case studies on your phoneBuilt into the site, saved as you go, there on your laptop when you sit down.
- Pin it to your home screenNo App Store and no Google Play. It is just there.
- No resit feesWork sent back is a chance to add more, with no resit fee.
- Return access for lifeQualify once and come back to the content whenever you need it.
- PT Manager from day onePT Manager is yours to learn on from the day you sign up. Using it with real clients comes once you hold your Level 3 and are listed on the FASTER Trainer Register.
- The FASTER Trainer RegisterA free listing on the Register once you qualify.
- Your certificates in one placeEvery course and its certificate on one page.
- Ask JohnThe Ask John button on every page, and his WhatsApp.
And PT Manager, free
53 tools to run your business, with no monthly fee and no cut of your money
PT Manager is yours to learn on from the day you sign up. Using it with real clients comes once you hold your Level 3 and are listed on the FASTER Trainer Register.
See all 53 tools
Set-up
- Import clients Bring a whole client list across in one go.
- My quotes Daily lines your clients see — yours, not stock.
- Programme templates The programme shapes you reuse — a session or twelve weeks. Pick one for a client, get your own copy.
- Exercise library Every exercise with FASTER coaching detail.
- Money Products, payments and who owes what.
- Send from your own email Connect your own email service so invites arrive from you, on your domain.
- My brand & client view What your clients see when they walk in — views, header, accent, logo.
- Your enrolment pack What every new client gets the moment you enrol them — your forms, ours, or a mix.
- Products and services What you sell — blocks, packages, memberships and one-offs, with their prices.
- Insurance Your policy on record — provider and expiry. Client features unlock while it is valid.
- My menu Switch any tool on or off — for your menu, your home and your whole account.
- Your website A free website on your own web address, filled from PT Manager. Or just the client sign-in door on your domain.
- Your public page Your verified Trainer Register listing, linking out to your own site and socials.
Business day to day
- Clients Your client list — invite, open a client, manage their space.
- Clubs Group your clients — a board they share, a programme or a monthly price if you want one.
- Challenges A dated push everyone logs against — for everyone you train, or for one club.
- Calendar Sessions, classes, capacity and bookings.
- Reminders The dates your business can't let lapse — insurance and first aid, nagged ahead of time.
- Nudges Who needs a nudge today — opportunities, one tap each.
- Who needs chasing Every conversation about money, in the order to work through them.
- What needs doing Your own list, in your own words — the jobs you keep meaning to get to.
- Till Sell at the desk — cash, card or on their phone — and download the sales sheet.
- What you are making What is coming in every month, what was paid in the last 30 days, and what sells.
Templates and systems
- Forms & interviews PAR-Q, consent, consultations and your own forms.
- Coaching room The coaching tools shelf — wheels, journeys and resources in one place.
- Radar wheels Build a life or performance wheel a client fills in — see change over time.
- Nutrition by FASTER Nutrition sheets and habits without meal-plan pretence.
- Pathways Automated coaching journeys you assign to clients.
- Programmes Start a programme — a session, a month, 12 weeks or a season — and find the ones you have built.
- Games & drills planner Build game-based sessions and drills.
- Sport screens Pick a sport — the shots to film, the analyser, and a ready-made radar of the qualities that matter.
- Movement screen → radar Read joint angles off the analyser — they auto-score and fill a radar wheel.
- Assessment builder Build and run client assessments and re-tests.
- Tag analytics Every tag across your clips, grouped and exportable.
Client
- AI prompts Your reusable prompt library for coaching copy.
- Workout library Short workouts your members put together by how they feel and how long they have.
- Before & after Side-by-side progress comparisons.
Trainer tools
- Exercise generator Fresh exercise ideas from constraints you set.
- FASTER dice & wheel Spin-and-roll session variety for groups and games.
- Movement demonstrator A 3D model of the FASTER movement patterns — body or skeleton view, prime movers lit up, live joint angles.
- Client video analysis Your media library — client folders and your own. Pick a clip to analyse.
- Movement by FASTER (HMAC) Human movement analysis charts — see how a client moves.
- Live analysis Mount your phone and coach live — skeleton, reps, angles and depth in real time.
- Tell a group One thing, to the right people — and you see exactly who it reaches first.
Media centre
- Video builder Reels, stories and client report videos, in your own branding.
- Image builder Branded posts and cards for your socials, at the right size.
- Shot list builder Every shot with its size, angle, lens, location, people, kit and sound; sorted into shooting order, ticked off on the day, printed or sent as a sheet.
- Storyboard builder Plan a video shot by shot: what the camera sees, what is said, the move and the cut.
- Script writer Write what you will say, with the word count and how long it takes to say.
- Teleprompter Read your script off the screen at your speed, and film yourself behind it.
- Content calendar Your hot topics, your series and every post planned by week and year, from idea to posted.
- Video and image organiser Everything you have made and every source you can pull from.
- Ad builder Make your own ads, coached as you go, in your branding. As many as you like, no fee, no cap.
Frequently asked
What is the all or nothing law?
When a nerve impulse reaches a motor unit, every muscle fibre in that unit is activated, or none is. It applies to the motor unit, not to the whole muscle.
What is a motor unit?
One motor neuron plus the muscle fibres it controls. A thigh motor unit can have thousands of fibres. A finger's has only a few.
Is this on the personal training course?
Yes. It is part of the anatomy, physiology and kinesiology unit that FASTER's Level 2 and Level 3 personal training course teaches.
When does PT Manager open?
PT Manager opens when you sign up with FASTER, and day one is for learning on. Real clients unlock once you have qualified and are on the Trainer Register.
Reading this for your own training? Every trainer on the FASTER register has been assessed by us — search by town or speciality, free.
Find a FASTER trainer →
