An underbar is how you pass feet-first through a gap, typically between two rails or under a single bar, using your hands on the bar to control your body as your legs lead the way through. The single most important rule: your feet lead, your hands steer, and you build up speed slowly, because this is one of the few parkour moves where rushing the progression puts your head directly at risk.
When You’d Actually Use One
The underbar solves a specific problem: a gap you need to get through rather than over. Double handrails, a fence with a horizontal gap, scaffolding, anywhere going over would cost more time and height than simply passing through. It also generates real forward momentum from a near-standing start, which makes it useful for linking into whatever comes next rather than just clearing the obstacle.
Step 1: Learn It Standing Still
Do not run at this on your first attempt. Stand beside the gap, put one leg through, then the other, then slowly work your torso through while holding the bar. The point is to learn exactly how much clearance your body actually needs, particularly your back and your head, which are the two parts most likely to make contact. Repeat this slow version until the spatial awareness is automatic.
Step 2: Get the Hand Position Right
Grip the top bar with an overhand grip. London Parkour’s underbar breakdown emphasises a detail beginners routinely skip: keeping both hands securely on the bar through the whole movement, which matters enormously if there’s a drop on the far side. It also recommends practising from both sides rather than only your comfortable one, an underbar you can only do left-handed is half a skill.
Step 3: Add the Approach
Once the slow version is clean, back up about five metres and approach at a medium pace, not a sprint. Take off roughly a metre and a half out, bring your legs together, and lift them toward the top bar so your feet enter the gap first. Your hands grab as your legs pass through, and you release once your upper body is clear.
Step 4: Arch, Don’t Look Forward
This is the counterintuitive part. During the swing through, your back should arch and your head should stay back rather than craning forward to see where you’re going. Looking forward flattens your back out, which is the most common cause of clipping your head on the bar. Trust the line you picked before you committed.
Choosing a Gap to Learn On
- Go low-to-high, not high-to-low: passing from a lower surface up to a higher one gives you far more control over your feet on landing
- Pick a generous gap first: narrow it only once the movement is consistent, never on the same session you’re also adding speed
- Check the bar is solid: underbars load a rail with your full bodyweight and momentum, a loose or rusted rail is not the place to find that out
Common Mistakes
- Leading with the head or torso instead of the feet: the fastest route to hitting the bar
- Releasing the bar too early: costs you control exactly when you need it, on landing
- Adding speed before the slow version is clean: speed hides nothing and forgives nothing here
- Only ever practising one direction: real obstacles won’t always suit your preferred side
Frequently Asked Questions
Is the underbar dangerous for beginners?
It carries real risk mainly from head and back contact with the bar, which is why every credible tutorial insists on the slow, stationary progression first. Learned in that order, on a generous gap, it’s genuinely one of the more approachable technical movements.
What’s the difference between an underbar and a 360 underbar?
The 360 adds a full twist of the body during the pass-through. It’s largely a freerunning variation, more expressive than efficient, and it should wait until the standard underbar is entirely reliable.
Do I need strong grip to do an underbar?
Some, though less than a cat leap or a hang. Your hands are steering and stabilising more than holding your full weight for long. That said, grip endurance work makes the movement feel considerably more secure, especially when there’s a drop on the far side.
Where to Go Next
The underbar sits alongside the other bar and rail skills. Read next: How to Build Grip Endurance Beyond Just Pull-Ups and 10 Parkour Vaults for Beginners.