Become a Personal Trainer
A New Client's Shaky Leg Is The Nervous System Learning The Movement
From the FASTER syllabus: this article is taught in full in The honest route from scratch to qualified →
In short: A client's leg shaking on a brand new movement is motor units, the neuron and every muscle fibre it controls, firing slightly out of sequence because the nervous system hasn't learned the pattern yet. Within a few weeks of practice those motor units start firing together instead, in a process called rate coding, and the shake disappears, and the client gets measurably stronger before their muscle has grown at all. One of the things you learn on our CIMSPA-recognised personal training course is what's actually happening in that shake, so a trainer can explain it in one sentence instead of guessing at it.
The shake isn't a problem to fix
A client's leg trembling through a set of a movement they've never done before looks, to most people watching, like something going wrong. It isn't. It's a motor unit, a single neuron and every muscle fibre it controls, firing slightly out of time with the others doing the same job. Nothing is failing. The nervous system just hasn't learned the pattern yet.
The question a new trainer doesn't want to be caught by
Somebody weighing up a career change into personal training can picture the moment easily enough: a first client, a new exercise, a visible shake, and a question hanging in the air that deserves a real answer, not a guess. One of the things you learn on our CIMSPA-recognised personal training course is exactly what's happening in that shake, in one sentence rather than a shrug.
What's happening underneath it
Skeletal muscle is made of fibres, and a motor neuron running down from the spinal cord controls a whole group of them at once, a motor unit. In a brand new movement, several motor units inside the same muscle fire slightly out of sequence with each other. That lack of coordination, not weakness, is what shows up as the shake and the drop in power a new client feels.
Give it a few weeks of the same movement and the picture changes. The motor units start firing together instead of out of step, a process the course calls rate coding, the connections between the nervous system and the muscle strengthen, and the shake disappears. The client gets measurably stronger in that window, and none of it came from the muscle getting any bigger.
Why that changes how the exercise gets coached
A trainer who doesn't know this reads an early shake as something to correct, or worse, as a sign the exercise was too hard and needs swapping out. A trainer who does know it can say, plainly, that this is the nervous system doing exactly what it's supposed to do on week one, and that it settles by week three or four on its own. That's a different conversation with a nervous new client, and it's the accurate one.
What to do next
Watching that shake settle over a few sessions is one of the clearest, most satisfying things a trainer gets to see, and it's worth naming out loud to the client rather than leaving it unremarked on.
PT Manager opens the moment you sign up with any FASTER course, and adding real clients unlocks the day you pass one. Read more about the Level 3 Personal Trainer Certificate this comes from.
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Also worth a look: Level 3 Personal Trainer — the anatomy unit this comes from.
See what the course covers →Frequently asked
Does the shake mean the client is doing the movement wrong?
No, it's a sign the nervous system hasn't learned the pattern yet, not a fault to fix, and it settles on its own within a few weeks of repeating the movement.
Does the client actually get stronger before their muscles grow?
Yes, the course text is specific on this: the early strength gain comes from the motor units firing in better sync, not from muscle size, which only starts adding to it later.
Does finishing the course get me PT Manager?
Yes. PT Manager opens the moment you sign up with FASTER, and adding real clients unlocks once you pass a course.
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