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Customers rate us 4.9/5 based on 1507 reviews.

40kg SmartBell Ninja™ Adjustable Dumbbells

8,068.00 kr 9,145.00 kr
  • Train Smarter with 1kg increments 
  • Adjust weights from 3kg to 40kg
  • One pair replaces 76 dumbbells in 1kg increments
  • Quality checked and come with 36 Months Warranty
  • Precision engineered knurling for advanced performance, grip and comfort.
🚚 FREE avg 2 day delivery
🛡️ 3-YEAR warranty on all dumbbells
😊 Over 75,000+ happy customers

Delivery and Shipping

We offer delivery to most EU countries. You can see a full list of delivery costs here. You can also check out our delivery FAQs here.

Why choose BrainGain
  • FREE and fast delivery across Europe
  • Rated EXCELLENT on Trustpilot
  • Over 100,000 adjustable dumbbells sold
  • Spread the cost with Klarna
  • 3 year warranty as standard

Overview

The 2026 SmartBell Ninja™ is our most advanced adjustable dumbbell.

One compact pair replaces an entire rack of 76 dumbbells.

Fast-change from 3kg to 40kg in 1kg increments. The Ninjas deliver 38 exact weight settings that can be cycled through in under 1 second, giving you total control over your strength-training goals without breaking your workout rhythm.

Eliminate downtime changing weights between sets and unnecessarily large jumps between weights when doing progression.

Matte steel plates provide durability with a refined finish. The brushed aluminium handle is ergonomically shaped with precision knurling for controlled grip under load. A patented safety-lock mechanism secures only the selected weight, while the steel base ensures stability at rest.

The Ninjas are designed for lifters who want to Train Smarter.

Features

3kg–40kg in 1kg increments
1 pair replaces 76 dumbbells
Fast twist-handle adjustment mechanism
Integrated safety-lock system
Steel plates
Brushed aluminium knurled handle
Stainless steel + nylon base

Warranty

All of our products come with a 3 year warranty as standard. During the warranty period we will repair or replace, at no charge, products or parts of the product defective because of improper materials or workmanship, under normal use and maintenance. Full Warranty Information can be found here.

For the most experienced iron-pumpers, while perfectly catering to beginners too.

The build quality is excellent. The knurled metal handle is the icing on the cake.

An industrial-strength set of weights with a smart design.

Robust... and comfy for most classic moves.

Ultra smooth and easy to twist... one of the sturdiest designs we tried.

  • Up to 38 dumbbells in 1

    Easily adjust from 3kg to 40kg in precise 1kg increments with the SmartBell Ninja™ Adjustable Dumbbells. One compact pair replaces 76 individual dumbbells, eliminating the need for bulky racks while giving you the exact weight you need for every set.

  • Total Body Workouts

    Adjustable Dumbbells can be used for all your home workout needs and exercises including presses, swings, deadlifts, squats, curls, sit-ups, snatch, renegade row, twists, clean & press, thrust and more.

  • Base

    The 40kg Adjustable Dumbbells come with their own tray to facilitate simple weight changes and tidy storage.

Your Body Is Already Losing Muscle

From age 30, your body naturally loses muscle mass. Without resistance training, it only gets worse.

3-5%

muscle mass lost per decade from age 30. After 50, this accelerates to 1-2% per year.1

10-17%

lower risk of all-cause mortality, cardiovascular disease and diabetes from strength training.2

30-60 min

per week is the optimal dose - just 3x 20-minute sessions for maximum longevity benefit.3

1 Source 2 Source 3 Source

Built Different. Here's the Proof.

We surveyed 659 BrainGain customers across 5 key markets.

90%

said the value justified the price or price wasn't even a concern.*

72%

train 3 or more times per week with their BrainGain dumbbells.*

81%

want to buy more BrainGain products (accessories, supplements, training).*

* Source: BrainGain Customer Survey, February 2026, n=659 across 5 markets.


INDEPENDENTLY TESTED

BrainGain adjustable dumbbells were tested by SaferBuy, an independent product verification institute, as mystery shoppers in October 2025.

97.5/100

Getting Started

100/100

Proofing – Product matches description

91.5/100

Packaging & Contents

0

Inconveniences found

SaferBuy Read the full report →

"Game-Changer for Home Workouts!"

These dumbbells are simply magnificent. They save space, time and money.
Structurally they are solid and aesthetically beautiful. In addition I must point out that they do not make any sound when shaken. Awesome price.

Michael, Trustpilot - Germany

DIMENSIONS

Length: 53 cm

Height: 19 cm

Width: 18 cm

Handle Length: 12 cm

Product Highlights

Explore the key features of our 40kg SmartBell Ninja™ Adjustable Dumbbells by clicking on the pulsing highlights.

Us vs. Them

Not overhyped or overpriced.
Just premium adjustable dumbbells built to last.

BrainGain
Generic Adjustable
Gym / Fixed Weights
Max weight
Up to 41.5kg
40kg
Depends on gym
Weight settings
Up to 26-in-1
10–17
Fixed
Change weight in 1 sec
No rattle during lifts
Replaces entire rack
3 year warranty
Premium support

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