Motor Unit Recruitment: Robbie Bourke on Isometrics

Based on Episode 68 of the Just Fly Performance Podcast, a conversation between host Joel Smith and strength coach Robbie Bourke.

Motor unit recruitment is the lever almost every strength method is secretly pulling, and Robbie Bourke thinks isometrics pull it better than most. Bourke, a Dublin-based strength coach, therapist, and host of the All Things Strength and Wellness podcast, starts from an unusually blunt premise: the brain is a survival organ that only ever asks whether something is safe, and training is a threat. What follows from that is a genuinely useful paradox. Reduce the threat to an athlete’s joints, and you free the nervous system to recruit more, work harder, and express force it was previously holding back.

Key Takeaways

• The nervous system is the real target. Exercises are just a means of getting at it, which is why no single lift is mandatory.
• Isometrics let athletes express force safely. Locked into a position, the brain senses safety, so it stops protecting and lets the athlete recruit.
• Cut orthopedic threat to raise neurological threat. A joint in a bad position triggers inhibition and caps force; fix the position and force goes up.
• Your weakest point defines your max. A 400-pound squat is a 400-pound squat only because the weakest joint angle says so.
• Partials are not cheating if they are specific. A heavy one-inch step-up makes sense once you look at a long jumper’s penultimate joint angles.

Why the brain caps your force

Bourke’s framing starts before any exercise selection. He treats the athlete as an organism whose brain is running one continuous calculation.

The brain is mainly concerned with survival. The brain’s just always asking itself two things: is it safe, or is this not safe? Training is a threat to the system. It’s a disruption in homeostasis.

From there, the question becomes how much of an athlete’s strength the brain is willing to release. That is where he has been focused, on the inhibition side rather than the muscle side.

I’m fascinated with neural inhibition, the muscle spindles and the GTOs. Motor unit recruitment is huge. Being able to activate and recruit motor units is a huge part of increasing biological output, of how much force we can produce.

He is careful to keep the tools in their place. In his view, the exercise is never the point.

What we’re manipulating is the organism, and the huge player in the organism is the nervous system. Strength training and all the exercises are just a means, one way to do it. That’s why you get Chris Korfist saying, I don’t really squat, because I don’t need that to tap into the nervous system.

The paradox: less orthopedic threat, more neurological threat

This is the most useful idea in the conversation. Bourke wants maximum threat to the nervous system and minimum threat to the joints, because the second one sabotages the first. He credits Dennis Logan for the example that made it concrete.

If I use a straight-bar back squat with guys who’ve got really restricted thoracic mobility and they can’t get that external rotation, they’re uncomfortable, and straight away that’s a threat to the body. That threat won’t allow them to express the most force they can. Put them in a safety bar and now I can get them to produce more force.

He resolves the apparent contradiction cleanly: the athlete in the safety bar is creating more threat to the system precisely because they are finally allowed to produce more force.

If the brain feels the body cannot produce force because a joint is in a bad position, it’ll come up with that arthrokinematic inhibition and won’t allow you to produce optimal force around the joint. We’re reducing orthopedic threat so we can raise the neurological threshold and dampen down neural inhibition.

Isometrics fit that brief almost perfectly, and Joel makes the point from the athlete’s side: locked into a position with a bar that is not going anywhere, the brain has little left to protect against, so the athlete can simply push. Bourke sees the same opening.

With isometrics you can maximally express force, and you can set up in a way where it’s safe in terms of the mechanics of the body, where we can maximally tap into some motor unit recruitment. How powerful can that be in damping down neural inhibition and allowing us to express more force?

Your weakest angle is your real maximum

Once you accept that inhibition is the limiter, the standard way of talking about strength starts to look sloppy. Bourke’s correction is worth stealing.

When people say my max squat is 400 pounds, it’s like, no it’s not. Your max full squat is 400 pounds, because your weakest point is going to be your limiting point.

That is why he is drawn to maximal isometrics held in the weakest positions, and why he is thinking through whether to pair them with the full movement in the same session or separate them onto different days. It is also why he defends partial-range work that the wider industry mocks, provided it matches the event. His example is Dan Pfaff’s work with long jumper Greg Rutherford.

People see it and say, that’s supposed to be a step-up? It’s only an inch. And I’m like, do you know what Greg Rutherford’s sport is? Have a look at his penultimate step when he goes into his jump. Look at those joint angles. Oh, now it starts to make sense.

Joel adds the historical footnote that undercuts the objection entirely: track and field has been doing half and quarter squats for fifty years. The squat below parallel is a rule for powerlifters, whose sport it is, not a law of training.

Train above the threshold you compete at

The survival framing also shapes how Bourke thinks about workload, an idea he traces to a conversation with Vern Gambetta.

Training needs to raise your threshold so that competition is actually submaximal. Your body’s like, this is nothing compared to what I’ve experienced in training. A lot of injuries happen because training doesn’t outstrip the threshold you need to surpass in competition, and then your body’s just not ready.

He rounds it off with the pattern he keeps noticing across otherwise unrelated systems: they all work the ends and let the middle take care of itself. Westside runs max effort and dynamic effort with repetition work between them; a track week runs acceleration at one end and tempo at the other. Isometrics, for him, are simply a precise way to attack one of those ends without asking the joints to pay for it.

Frequently asked questions

What is motor unit recruitment, and why does it matter?
It is the nervous system’s ability to activate motor units to produce force, and Bourke considers it one of the main drivers of an athlete’s output. His argument is that most athletes are limited less by muscle than by neural inhibition, so the training question becomes how to get the brain to release more of the force that is already there.

Why are isometrics good for motor unit recruitment?
Because they let an athlete express maximal force in a mechanically safe position. Locked into a hold, there is little orthopedic threat for the brain to protect against, so it permits more recruitment. Bourke also uses them at specific joint angles and as a potentiation method before dynamic work.

What is the orthopedic versus neurological threat paradox?
Bourke wants high threat to the nervous system and low threat to the joints. If a joint sits in a compromised position, the brain applies what he calls arthrokinematic inhibition and caps force output. Removing that constraint, as with a safety bar for an athlete with restricted thoracic mobility, lets the athlete produce more force, which is itself a bigger stimulus.

Is a partial squat or a one-inch step-up legitimate training?
It depends entirely on the sport. Bourke points to Dan Pfaff’s heavy, tiny-range step-ups with long jumper Greg Rutherford: once you look at the joint angles of a long jumper’s penultimate step, the range makes sense. Below-parallel squatting is a requirement of powerlifting, not a universal standard.

How hard should training be relative to competition?
Harder. Citing Vern Gambetta, Bourke argues training should raise an athlete’s threshold so that competition feels submaximal, and that many injuries occur when training never exceeds the demands the athlete eventually meets in a game.

About the authors

Robbie Bourke is a strength and conditioning coach, neuromuscular therapist, and holistic health and nutrition practitioner based in Dublin, Ireland, and the host of the All Things Strength and Wellness podcast. He has coached primarily in hurling and Gaelic football and has spent time at Mike Boyle Strength and Conditioning in Boston and at ALTIS in Phoenix, and he is known for pulling strength and conditioning, rehabilitation, nutrition, and neuroscience into a single view of the athlete.

Joel Smith is the host of the Just Fly Performance Podcast and the founder of Just Fly Sports, a former collegiate strength and track and field coach focused on speed, power, and athletic development. Listen to the full episode with Robbie Bourke on Just Fly Sports.