What machine did Will Tennyson call the hardest workout machine?

An ARX - an adaptive resistance machine whose computer-controlled motor matches the exact force you produce on every rep, including the lowering phase. His 60-second set has been viewed more than 18 million times.

Why is an ARX machine so hard?

There is no weight to select. The motor pushes back exactly as hard as you push, so every rep is maximal by definition - and the machine loads the lowering (eccentric) phase, where you are strongest, which ordinary weights cannot fully resist.

Is ARX too hard for beginners or older adults?

No - the resistance can never exceed the force you produce, so maximum effort is always your maximum. There is also a Static Protocol (a non-moving hold) used for rehab, injury, and deconditioned users.

The Hardest Workout Machine You’ll Ever Try? 19 Million People Watched Someone Find Out

Will Tennyson has trained with everything the fitness industry makes — and one machine made him look like it was his first day in a gym. Not because he’s weak. Because ARX refuses to let a single rep be easier than your absolute maximum. No stack to pick, no plates to strip: a motor that matches whatever force you bring, every inch up and every inch down. He called it “the hardest workout machine you’ll ever try” — and 18.9 million people watched him find out why.

18.9M views

What is he actually fighting?

Not a weight. An ARX has a computer-controlled motor instead of a stack, and the motor obeys one rule: push back exactly as hard as you push. There is no number to select and no setting to cheat. If you give 100%, the machine gives 100% back — on every inch of the range, on every rep.

That’s why the face he makes in the video happens. On a barbell, the load is fixed and most of the rep is easier than your true maximum. On an ARX, there is no easy part of the rep — the resistance is always yours, at full effort, wherever you are in the movement.

The lowering phase is the secret

Your muscles are stronger lowering a weight than lifting it — which means ordinary weights can never fully load the phase where you’re strongest. The ARX motor can. It resists the lowering (eccentric) phase at your true maximum too, and that eccentric loading is what drives the most muscle and bone adaptation. It’s the part of the video where he looks like he’s losing an arm-wrestle with a robot — because, mechanically, he is.

Watch the full test

The Short came from a longer experiment — Will testing the world’s most scientific training machines. The five minutes below are the ARX segment: the motor matching him rep for rep, with the force data on screen.

“Hardest” doesn’t mean it’s not for you

Here’s the twist most of those 19 million viewers missed: the same mechanism that makes ARX maximally hard for a YouTuber with a big bench also makes it exactly matched for a 70-year-old, a post-surgery knee, or someone who hasn’t trained in a decade. The resistance can never exceed the force you produce — so “maximum effort” is always your maximum, never a weight you can drop. There’s even a Static Protocol — a non-moving hold — used for rehab and deconditioned users.

Hard and safe aren’t opposites on this machine. They’re the same feature.

The numbers behind the faces

In an independent 12-week study comparing ARX to traditional weight training, the ARX group saw 2× the muscle gains and 90% greater strength gains — in 72% less training time.* Every rep is also measured: force produced, both directions, every session, so progress is a chart instead of a feeling.

Try the thing 19 million people watched

One machine, under 40 square feet, a complete full-body workout in about 15 minutes. In your home, or as the anchor of a studio.

Talk to ARX

* Study details and references: arxfit.com/terms-of-services#references. Video by Will Tennyson, embedded from YouTube.