The Most Important Thing You Can Do To Build Strength

ELI5/TLDR

Strength is not just about how big a muscle is. It’s also about how much of that muscle your nervous system is willing to actually use. Most untrained people, even when they think they’re pushing as hard as they can, are only really firing 70-85% of the muscle. Heavy lifting trains the brain to release the safety brake and recruit more of what’s already there. The practical kicker: you only need 3-6 hard sets per muscle group per week, at 80-100% of your one rep max for 1-6 reps, to get and stay strong. And it matters more as you age, because the muscle fibres that disappear first are exactly the ones that only wake up under heavy load.

The Full Story

Strength is a force question, not a size question

Start with the definition. Strength is how much force a muscle or muscle group can produce in a single contraction. The cleanest way to measure it is a one rep max — the heaviest squat, bench, or deadlift you can do exactly once. That’s it. Not how long you can hold the weight. Not how many reps you can grind out. Just peak force.

This puts it next to two other muscular adaptations on the same shelf, but they’re different animals. Muscular endurance is low force, lots of repetitions — chair pose, a long run, holding a plank. Hypertrophy is the middle of the dial — moderate weight, 8-12 reps, and the muscle gets bigger. Strength sits at the heavy end — 1-6 reps at 80-100% of your max.

Think of it like a stereo dial of contraction intensity. Endurance lives at the quiet end (30-60% of one rep max), hypertrophy in the middle (60-80%), strength at the loud end (80-100%). There’s overlap — bodybuilders are pretty strong, and trail runners doing hill climbs grow bigger thighs than road runners — but if you want to specialise, you have to spend time at that end of the dial.

Why a powerlifter outlifts a bigger bodybuilder

Here’s the puzzle the video opens with: powerlifters often outlift bodybuilders despite being smaller. The size of the muscle clearly matters — bigger muscles have more contractile proteins (the tiny molecular ratchets that pull your bones around), and more of those means more force. But size isn’t the whole story.

Some of the size you see on a bodybuilder is fluid and glycogen — water and stored carbs sitting in the muscle. Useful for getting through a high-volume session and recovering between sets, but they don’t directly add force. Which means a smaller, drier muscle can sometimes outpunch a bigger, juicier one.

The bigger explanation is wiring.

The motor unit — a wire and the fibres it controls

Every voluntary movement starts as a signal in the motor cortex of your brain. That signal hops down to the spinal cord via an upper motor neuron, then a lower motor neuron carries it out through a nerve and into the muscle, where it connects to a bunch of muscle fibres at a junction called the neuromuscular junction. The lower motor neuron plus all the muscle fibres it controls is called a motor unit.

Motor units come in different sizes. The ones that move your eyes are tiny — one neuron talking to maybe 6-10 fibres, perfect for fine control. The ones in your quads are huge — one neuron talking to thousands of fibres at once. When that one neuron fires, every single fibre it’s connected to contracts. All or nothing.

A muscle has many motor units inside it, and you don’t fire them all at once when you lift something. Your body grades the recruitment to the task. Light load? A few small motor units. Heavier load? It pulls in more, and bigger ones. This is motor unit recruitment, and it’s the second engine of strength.

Your nervous system has trust issues

Here’s the surprising bit. If you take an untrained person, hook them up to equipment that can read motor unit activity, and tell them to contract as hard as they possibly can, they only fire 70-85% of their motor units. They feel like they’re maxed out. They aren’t.

Why? The nervous system is protecting you. If you had instant voluntary access to 100% of every muscle, you’d tear soft tissue, snap tendons, herniate discs. So the brain keeps a chunk of muscle in reserve, behind a safety brake. This is neuromuscular inhibition.

Heavy strength training is, in part, a slow conversation with the nervous system. Lift heavy enough, often enough, and the brain starts to trust you. The brake eases. A trained person can voluntarily recruit 90%+ of their motor units. The nervous system also gets faster at recruiting them, fires them at higher frequencies, and coordinates the timing across muscles better. All of this means more force without any extra meat on the bone — exactly how the powerlifter outlifts the bigger bodybuilder.

Why this matters more as you age

Each motor unit only contains one type of fibre — either slow twitch (low force, fatigue-resistant — the marathon engine) or fast twitch (high force, quick velocity, fatigues quickly — the sprint engine). The body recruits them in order. Slow twitch first, all the way up the chain. Fast twitch fibres don’t really come online until you cross 60-70% of your one rep max, and they’re not properly stimulated until you’re at 80%+.

Now the kicker: as you age, the fast twitch fibres are the first to atrophy. And the reason is mostly use-it-or-lose-it. Walking, gardening, cycling, even a long run — none of these recruit those higher-threshold motor units. So if your “exercise” is only steady-state cardio and pottering around the house, the fast twitch wing of your muscular system is steadily going dark. The only thing that wakes it up is heavy load.

That’s why strength training quietly outranks the other two for longevity. It’s the only stimulus that keeps the fibres responsible for catching yourself when you trip, getting up off the floor, lifting a grandchild — alive.

Key Takeaways

The actual prescription

Load: 80-100% of your one rep max
Reps: 1-6 per set
Volume to maintain & make modest gains: 3-6 hard sets per muscle group per week
Volume to build strength faster: 6-10 hard sets per muscle group per week
Frequency: As little as one strength session per week is enough to keep and slowly grow strength, provided you actually show up for it

Three workout splits the host suggests

One strength day a week (full body): pick four big compound lifts — one upper push (bench), one upper pull (pull-ups), one lower push (squat), one lower pull (deadlift). Add a single-leg accessory and some calf work if there’s time.
Two strength days split into upper / lower, with more accessory work — shoulder press, rows, hamstring curls, hip thrusts, single-leg work.
Every other day (his favourite for a generalist): Mon/Wed/Fri strength alternating upper-lower across two-week cycles, Tue/Thu zone-2 cardio for 45-60 min, Sat a hard 4x4 interval session.

The non-negotiable: consistency. A once-a-week plan only works if you actually do it once a week.

Claude’s Take

Solid 8/10. The Institute of Human Anatomy guys are good at this format — they show actual cadaver tissue, anchor every claim in the underlying anatomy, and don’t overreach. The neuromuscular-inhibition story is the real meat here, and it’s an idea that doesn’t get enough airtime in fitness content. Most people think “get stronger” means “get bigger,” and the motor-unit-recruitment angle reframes the whole thing.

The longevity argument lands too. The fast-twitch atrophy point is the right hill to die on if you want to convince a 37-year-old who already runs and cycles to start lifting heavy. Cardio alone won’t reach those fibres, and they’re the ones that go first.

The minor demerit: about 90 seconds of the runtime is a creatine-electrolyte sponsor read that I’d ignore — fine product, but the framing leans more advert than analysis. The actual physiology content is clean.

One thing worth noting that the video glosses over — the “80-100% of one rep max for 1-6 reps” prescription assumes you have a good handle on your one rep max and decent technique. For someone starting fresh, the first few months of any resistance training will produce strength gains anyway (the “newbie gains” he mentions), and the more important variable is just learning the movement patterns safely. Heavy singles are not where a beginner should start.