Cable One Arm Tricep Extension
A single-handle pushdown taken underhand: elbow pinned to your ribs, forearm driving down until the arm is straight. Working one side at a time exposes the arm that has been coasting behind a two-handed bar, and the supinated grip keeps the elbow tucked instead of letting the shoulder roll in to help.
Own the movement
Set up first, then execute. Every cue below is something you can check on your next set.
Before the first rep
- Clip a single handle to the high pulley and stand one step in front of the stack, facing it.
- Take the handle underhand and pull it down until the upper arm is glued to your side and the elbow points at the floor.
- Split your stance, one foot forward, so the cable cannot rock you toward the machine.
- Rest your free hand on your hip or the frame - do not brace it against your working elbow.
Every rep
Breathing & tempo — Exhale as you press down, inhale as the handle returns. One second down, a one-second squeeze at lockout, two seconds back up.
Sets, reps & load
Where to start, and what to change when it stops being hard.
Start at about a third of what you use on a two-handed bar pushdown - often 5-10 kg on the stack - and expect it to feel heavier than the arithmetic suggests, because nothing is stabilising you against the pull. Good looks like a motionless upper arm and a full lockout on the weaker side's last rep. Add weight only when both arms reach the top of the range.
What goes wrong
The errors that show up most often, and the cue that fixes each one.
Stand upright in a split stance with your shoulders behind the front foot. If you still have to lean to finish a rep, take a plate off the stack.
Pin the upper arm to your side and hold light pressure against it with your torso for the whole set. Reduce the load until the elbow stops travelling on the last two reps.
Straighten the arm completely on every rep and pause for a count of one. A pushdown that never locks skips the part of the range the triceps is strongest through.
Start each set with the weaker arm, count its reps, then give the stronger arm exactly that many. Equalising volume is the entire reason to work one side at a time.
Why bother
Any two-handed pushdown lets the stronger arm quietly take a bigger share of the stack. One handle removes that option: the weight you can finish ten clean reps with is the weight that arm genuinely handles, and the gap between sides is usually larger than people expect to find.
The underhand grip is often sold as a way to target the medial head. Treat that as marginal at best - no grip lets you choose which head does the work, since all three share one tendon and one job at the elbow. What supination actually buys you is a tucked elbow and a shoulder that cannot rotate in to cheat.
Where it fits
At the end of a push session, 2-3 sets per arm of 12-15, starting with your weaker side so it sets the rep count. This is a finisher rather than a foundation - the usable load is capped by how well you can pin the elbow, not by triceps strength.
If this one isn't it
No kit, too hard, or too easy — here's where to go instead.
Same job, different kit
Start here instead
When this gets easy
Asked and answered
Does an underhand grip really hit the medial head?
Not in any way you can feel or measure reliably. All three heads share one tendon and one action at the elbow, and rotating the forearm does not switch between them. Use the underhand grip because it keeps the elbow tight and the wrist comfortable, not because it isolates anything in particular.
My weaker arm is well behind. Should I give it extra sets?
One extra set on the weak side at most, and only while the gap is obvious. The faster fix is running every set to the weaker arm's rep count so the stronger side stops piling up extra volume. Expect the difference to close over months, not weeks.
Is this better than a rope pushdown?
Better for finding and fixing a side-to-side difference; worse for total load and for time spent. Keep a two-handed pushdown as your main pressing-down movement and use this when one arm is visibly lagging or your elbows want a lighter day.
Can I do it kneeling or from a low pulley?
Kneeling removes the temptation to lean and is a sensible swap if you keep cheating with bodyweight. A low pulley makes it a different movement entirely - an overhead or behind-the-body extension - where the stretch, not the lockout, is the hard part.