Developed by Fré Leys

Train the strength
that hangboards forget.

Traditional hangboards focus 100% on crimps (2 finger flexors). Sloper King™ is the ultra-lightweight (<100g) biomechanical trainer that activates all 4 primary forearm and wrist flexors to dominate open slopers and delay forearm pump — without overloading your finger pulleys.

4
Muscles Active
Pulley Safe
0% Joint Strain
5 Angles
Adjustable Difficulty
< 100g
Pocket Size
PHOTO PLACEHOLDER • HERO PRODUCT SHOT
What to showcase here: Clean close-up action photo of Fré gripping the Sloper King on the climbing wall or cable machine, highlighting active wrist flexion, deep forearm muscle tension, and the matte black finish with yellow mascot crown.

Sloper King™

Single piece (€24.95) or Pair with pouch (€44.95)

From €24.95
In stock
  • Single Unit (€24.95): 1x Sloper King + 800kg cord + Guide
  • Complete Pair (€44.95): 2x units + 2x cords + Cotton Pouch + Guide
  • CROP GoldX 220-grit high-friction contact strips
  • 5 adjustable difficulty angles on every unit
Free local pickup in Leuven
BE €3.99 | EU €4.99 Tracked
Made in Belgium
15-MINUTE MASTERCLASS & ORIGIN DOCU

Why Slopers Feel Impossible & How I Accidentally Engineered the Ultimate Pump Trainer

Watch the complete 15-minute breakdown where Fré Leys (PhD.) breaks down sloper biomechanics, shows the 100kg break test, and explains cable-machine endurance protocols.

YouTube Video Thumbnail Placeholder
14:48 • 4K UHD
[ YOUTUBE VIDEO PLACEHOLDER ]

"The Biomechanics of Slopers vs. Crimps (And the Tool I Built)"

Click to view the video chapters and director's structure.

0:00 - 3:15
1. The World Cup Failure
Pumping out on 3 slopers vs 2nd place in Quali 2.
3:15 - 6:40
2. Biomechanics Gap
Why hangboards only isolate 2 muscles instead of 4.
6:40 - 9:50
3. 3D & 800kg Test
Decoupling load to the semi-static cord.
9:50 - 13:10
4. The Pump Discovery
Gym cable machine protocol & deep fatigue.
13:10 - 14:48
5. Gym Reactions
Live tester feedback in Boulder Leuven + CTA.
DIRECTOR'S NOTE FOR YOUTUBE VIDEO 1

Once you have filmed and uploaded the 15-minute video to YouTube: replace the placeholder with a responsive <iframe src="https://www.youtube.com/embed/YOUR_VIDEO_ID">. Anyone scanning the QR code in climbing gyms will immediately view this video in 4K.

Fré Leys (PhD.) - Para Climber, Inventor & Engineer
Inventor
2x World Cup Gold Medalist
Fré Leys (PhD.)
Belgian Para Climbing Team • Road to LA 2028

Inventor

Founder of BamBum. Bambum designs, prototypes and produces smart athletic hardware and software training tools that solve real performance bottlenecks.

Para Climber

2x IFSC World Cup Gold Medalist and Belgian National Team athlete competing at the highest international level aiming for the 2028 Paralympics.

Athlete Representative

Official World Climbing Athlete Representative. Giving a global voice to athletes and actively shaping the future of competitive Para Climbing.

PhD in Mechanics

PhD in Mechanical Engineering from KU Leuven. Specialized in robotics, mechanism design, kinematics, and the mechanical modeling of biological systems.

Direct Funding for LA 2028 ParalympicsHistoric Paralympic Debut

100% of all profits from Sloper King™ directly fund Fré’s international qualification campaign and coaching for the LA 2028 Paralympic Games — marking the historic first time Para Climbing is an official Paralympic sport.

Explore Fré's Road to LA 2028Follow the journey, engineering projects & international competitions
THE ORIGIN STORY

How a Brutal World Championship Failure Led to an Engineering Breakthrough.

PHOTO PLACEHOLDER • 2025 WORLD CHAMPIONSHIPS ACTION SHOT
What to showcase here: High-intensity competition photo of Fré on the competition wall during a World Cup or World Championship route to immediately anchor the athletic context.

"At the 2025 Para Climbing World Championships, I was in peak physical shape and climbing stronger than ever. But in the first qualification route, three consecutive open slopers shut me down. My forearms pumped out completely, my fingers peeled off millimeter by millimeter, and I fell: 11th place. In the second route, I placed 2nd and made finals. But the lesson was unmistakable: on open slopers, I was vulnerable."

Fré Leys (PhD.)
• 2x World Cup Gold Medalist, KU Leuven Mechanical Engineering PhD

As an engineer and an elite athlete, I refused to just accept that limitation. Why was my performance on crimps world-class, while I struggled on slopers?

The answer was in the training tools: I had spent years training on standard hangboards and Kilterboards. But those tools isolate the fingers in a closed crimp position. When I sat down to model the biomechanics, the anatomical blind spot became obvious.

SCIENCE & ANATOMY

Why Slopers Demand 4 Muscles & Full Forearm Contraction

Traditional hangboards only load your finger flexors on crimps with a passive wrist. Sloper King™ trains your finger flexors while actively contracting both wrist flexors across all 4 primary muscles simultaneously.

ILLUSTRATION / 3D ANATOMY GRAPHIC PLACEHOLDER
What to showcase here: Forearm anatomical cross-section diagram comparing isolated finger flexors (FDP/FDS) with active wrist flexors (FCR/FCU) contracting during an open sloper grip.
Traditional Hangboard (Crimp)

Only 2 Muscles (Passive Wrist)

Fingers hook onto edges with an extended/passive wrist, leaving the wrist flexors completely disengaged.

1
Flexor digitorum profundus (FDP)
Flexes fingertips on crimp edges.
2
Flexor digitorum superficialis (FDS)
Flexes middle joints on crimp edges.
The Joint-Angle Blindspot: Muscle strength is joint-angle specific. Strength gained holding edges with an extended wrist has near-zero carryover to the active wrist contraction needed on slopers.
High peak shear stress on A2/A4 finger pulleys (injury prone).
Sloper King™ Activation

All 4 Muscles (Active Contraction)

Engages finger flexors while actively contracting both wrist flexors inward to generate true sloper friction.

1. FDP (Finger Flexor): Active finger grip tension
2. FDS (Finger Flexor): Deep isometric hold tension
3. Flexor carpi radialis (FCR): Actively contracts thumb-side wrist flexor
4. Flexor carpi ulnaris (FCU): Actively contracts pinky-side wrist flexor
Direct Sloper Transfer: Training finger flexors alongside active wrist flexion contraction transfers 1:1 to real-world slopers.
Zero lever pressure on pulleys: 100% tendon-safe deep pump training.

The Accidental Discovery: The "Pump Master"

"When I rigged the Sloper King to a cable machine at the gym, I discovered something unexpected: because 4 muscles fire under continuous isometric tension while finger joints remain open and unpinched, it delivers the most intense and tendon-safe forearm pump training I've ever experienced. You can train forearm endurance to absolute muscular failure with zero pulley injury risk."

ENGINEERING & CONSTRUCTION

Mechanically Decoupled: 800 kg Load Capacity in <100 Grams.

Rather than building a heavy, fragile 3D block, we fully decoupled the load-bearing function from the ergonomic contact surface.

PHOTO PLACEHOLDER • CAD PROTOTYPES & 100KG BREAK-TEST RIG
What to showcase here: Photo of the CAD prototype evolution next to the final production model with the 220-grit contact surface, plus a screenshot of the 100 kg pull-force load test on the semi-static cord.

800 kg Semi-Static Cord

The 4mm semi-static load cord carries 100% of the tensile load (800 kg per strand, doubled = 1,600 kg theoretical). Tested beyond 100kg+ bodyweight.

220-Grit GoldX Friction

Because plastic is too slick, the ergonomic concave shell is surfaced with CROP GoldX 220-grit grip sandpaper. A reliable, predictable friction coefficient without tearing skin.

5 Cantilever Angles

Easily shift the cord across 5 numbered positions to adjust the difficulty from a subtle open-hand surface to an aggressive, hanging sloper.

4 TRAINING DISCIPLINES

4 Ways to Train Your Forearms & Grip

From pinpoint hypertrophy and deep pump resistance on cable machines to tendon-safe warmups at the crag.

FRÉ'S CHOICE ★★★

1. Gym Cable Machine

Attach to the pulley of a cable crossover. Dial in the exact resistance in kilograms for maximum muscular contraction.

VIDEO / GIF PLACEHOLDER

What to showcase: 15-second clip of Fré at the gym cable station (25kg hold, wrists curled inward, full forearm muscle activation).

Goal: Max Strength & Pump
5–7s heavy holds or 35–45s continuous tension (fatigue delay).
MOBILE STRENGTH

2. Floor Pick-Ups

Loop the Sloper King onto a kettlebell or weight plate loading pin and deadlift straight off the floor.

VIDEO / GIF PLACEHOLDER

What to showcase: Short clip lifting a 16–24 kg kettlebell off the floor with a locked, neutral wrist.

Goal: Home & Free Weights
No pull-up bar needed. Simple progressive overloading.
BODYWEIGHT

3. Pull-Up Bar & Counter

Hang the tool over a pull-up bar at home or at the gym for isometric bodyweight sessions.

VIDEO / GIF PLACEHOLDER

What to showcase: Fré hanging from an overhead bar on both Sloper Kings (with feet on ground or resistance band).

Goal: Isometric Hangboard
Offset hangs, active shoulder engagement, and core stability.
INJURY-SAFE

4. Crag & Pre-Climb Warmup

Gradually recruit your fingers and wrist flexors at the crag or gym without stressing finger pulleys.

VIDEO / GIF PLACEHOLDER

What to showcase: Warming up at the crag (Freyr/Fontainebleau or gym) with foot-loop progressive isometric traction.

Goal: Pulley Protection (<100g)
No heavy wooden boards to carry. Fits straight into your pocket.
UNBOXING & DELIVERABLES

What's inside your Sloper King™ package?

PHOTO PLACEHOLDER • UNBOXING FLAT-LAY PACKAGING SHOT
What to showcase here: Clean flat-lay photo on a light background showing: 2x matte black Sloper Kings with gold crowns, 2x 800kg semi-static load cords, soft cotton pouch, and the Tiny Quickstart training guide.
2x Sloper King™

High-durability matte black PLA with 5 adjustable cantilever positions.

2x 800kg Cords

4mm semi-static cord (800kg tensile load rating per strand).

1x Cotton Pouch

Custom soft cotton carry pouch.

1x Tiny Guide

Pocket Quickstart guide with QR codes to video protocols & diagrams.

COMMUNITY & ATHLETE REVIEWS

Trained by Climbers.
Tag #sloperking

From World Cup athletes to local gym crushers and Fontainebleau boulderers — see how the community trains sloper friction and pump endurance.

S
@sam_climber
Boulder Klup, Leuven
Boulderer (V8/7B+)
USER PHOTO
#sloperking
PHOTO PLACEHOLDER: Action shot gripping Sloper King on cable pulley at 30kg load with chalk dust.
Cable Machine 4x7s Repeater

"The active wrist pump after a 4-set repeater is wild. Never felt my forearms activate like this on standard hangboards."

#sloperking#bouldering#pumptraining
142 likes
3d ago
E
@elena.outdoors
Fontainebleau, France
Bleau Boulderer
USER PHOTO
#sloperking
PHOTO PLACEHOLDER: Outdoor session pulling against foot-loop cord in the Fontainebleau forest.
Foot-Loop Crag Warmup

"Under 100g so it lives in my chalk bag. Warmed up on slopers right at the boulders in Franchard before projecting."

#sloperking#fontainebleau#cragwarmup
289 likes
1w ago
A
@alex_paraclimb
Innsbruck, Austria
Adaptive Climber
USER PHOTO
#sloperking
PHOTO PLACEHOLDER: Gym workout with loading pin and 20kg bumper plate, focusing on wrist flexion.
Tendon-Safe Rehab Pulls

"Coming back from an A2 pulley tweak. Sloper King lets me train intense forearm endurance with 0% pulley shear stress."

#sloperking#paraclimbing#tendonsafe
215 likes
2w ago
M
@routesetter_marc
Brussels, Belgium
Commercial Route Setter
USER PHOTO
#sloperking
PHOTO PLACEHOLDER: Adjusting cord position on notch 4 before testing compression strength.
5-Angle Cantilever Testing

"The 5 angle settings let us match the exact slope of comp fiberglass volumes during test climbs."

#sloperking#routesetting#compclimbing
178 likes
2w ago
S
@sarah.beta
Klimax, Puurs
Lead Climber (8a)
USER PHOTO
#sloperking
PHOTO PLACEHOLDER: Dual Sloper Kings hung from pullup bar, dual-hand compression hold.
Bilateral Pair Compression

"Grabbed the complete pair. Doing dual-handed isometric lock-offs while timing intervals on the timer app."

#sloperking#climbingtraining#endurance
310 likes
3w ago
D
@boulder_dan
Ghent, Belgium
Gym Climber
USER PHOTO
#sloperking
PHOTO PLACEHOLDER: Close-up of open palm wrapping around the curved sloper surface with mascot crown.
GoldX 220-Grit Grip Test

"The 220-grit high-friction contact strips give realistic hold feel. Unlocks friction power I never knew I had."

#sloperking#boulderlife#climbinggear
95 likes
4w ago
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OFFICIAL WEBSHOP

Order Your Sloper King™

Made in Belgium. 100% of profits fund Fré's bid for the LA 2028 Paralympic Games — the historic first time Para Climbing is an official Paralympic sport.

Click a card to select
MOST POPULAR
PHOTO • COMPLETE PAIR
What to showcase: 2x matte black Sloper Kings with yellow crowns, 2x 800kg load cords, soft cotton carry pouch & guide.
Dual-Hand Bilateral Training

Complete Training Pair

€44.95

Full pair for dual-hand hangs, pull-up bar holds & bilateral pump training.

  • 2x Sloper King™ units (<100g each)
  • 2x 800kg semi-static load cords
  • 1x Soft cotton carry pouch included
  • 1x Tiny Quickstart Guide with video protocols
  • 5 difficulty angles on each unit
Selected (Complete Pair)
STARTER
PHOTO • SINGLE UNIT
What to showcase: 1x matte black Sloper King with yellow crown, 1x 800kg load cord & Tiny Quickstart Guide.
Unilateral Cable & Lift Setup

Single Unit (1 Piece)

€24.95

Ideal for unilateral cable pulls, loading pin lifts & portable crag warmups.

  • 1x Sloper King™ unit (<100g)
  • 1x 800kg semi-static load cord
  • 1x Tiny Quickstart Guide with video protocols
  • 5 difficulty angles built-in
  • —Carry pouch not included
Select Single Unit
Leuven Pickup
FREE (€0.00)
Local pickup by appointment
Belgium (bpost)
€3.99
With Track & Trace
European Union
€4.99
Tracked across EU (NL, FR, DE...)

Order Summary

Batch 1 • In Stock
Sloper King™ Set of 2 (Pair)
€44.95 per unit
1
Subtotal (1x Pair)€44.95
Shipping (Belgium)€3.99
Total Amount
€48.94

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OPEN SOURCE (CC BY-NC 4.0)

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Because I believe in open scientific innovation, I share the official 3D files free for personal, non-commercial use. Enter your email to instantly receive the STL bundle + the Slicing & Safety Guide.

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CLIMBING GYMS & COACHES

Want a Sloper King™ Test-Stand in your Climbing Gym?

We provide a free warmup test-stand for your training area and an 8-set retail display box on 100% consignment (zero financial risk). Your gym keeps €16 margin per set.

Request a Gym Package via fre@fre2028.la
FREQUENTLY ASKED QUESTIONS

Everything you need to know

Why is the cord decoupled from the 3D-printed body?

3D-printed plastics can delaminate under extreme shear torque. By looping an 800 kg semi-static cord directly through the cantilever channels, the cord carries 100% of the load. The 3D print serves purely as an ergonomic, anatomical contact shell.

Can I replace the grip sandpaper when worn out?

Yes! We use CROP GoldX 220-grit sandpaper with self-adhesive backing. You simply peel off the worn strip and apply a fresh pre-cut strip in seconds.

Why train on a gym cable machine rather than regular pull-ups?

On an overhead pull-up bar, you are always constrained to 100% of your bodyweight (unless using counterweight pulleys). On a gym cable machine, you can dial in the load down to the exact kilogram (e.g. 15 kg or 35 kg). This enables targeted hypertrophy and sustained isometric fatigue sets (35–45s continuous tension).

What is the estimated delivery time?

Batch 1 is locally produced in Belgium and dispatched within 2 to 4 business days via bpost (with Track & Trace across Europe). Local pickup orders in Leuven are usually ready within 24 hours.