| Tool | FlexionClosing the grip | ExtensionStabilising under load | Pronation/SupinationRotation — SkiErg, Carry | Endurance45-min race demand | Hyrox VerdictOVERALL RATING |
|---|---|---|---|---|---|
| Spring Gripper£8–£30 | ✓Good | ✗None | ✗None | ◎Limited | 1 of 4 planesTrains the squeeze. Ignores everything else. |
| Dead HangPull-up bar | ✓Good | ✗None | ✗None | ✓Good | 1 of 4 planesBuilds flexor endurance. Extensors untrained. |
| Fat Grips / Thick Bar£20–£60 | ✓Good | ◎Partial | ✗None | ◎Moderate | 1.5 of 4 planesBetter than grippers. Still misses rotation. |
| Wrist CurlsBarbell/dumbbell | ✓Good | ◎Partial | ✗None | ✗Poor | 1.5 of 4 planes30° range of motion. Race demands 360°. |
| Wrist RollerDIY or £15–£40 | ✓Good | ◎Partial | ✓Good | ◎Moderate | 2.5 of 4 planesClosest alternative. No internal resistance. |
| Gripzilla DynamoHyrox-specific | ✓Excellent | ✓Excellent | ✓Excellent | ✓Excellent | 4 of 4 planesThe only tool that closes all gaps. |
Every conventional grip tool — grippers, hangs, fat grips, wrist curls — loads the forearm in one direction: flexion. Closing the hand. Squeezing. Holding. These are the flexor muscles on the palm side of the forearm.
The muscles on the back of the forearm — the extensors — do the opposite: they open the hand, stabilise the wrist under load, and prevent the grip from collapsing when the flexors are exhausted. In a Hyrox race, these are the muscles that decide whether you drop the bells at metre 80 or carry them to metre 200.
The Dynamo's internal friction plate creates oppositional dual-directional tension: forward rotation loads the flexors, reverse rotation loads the extensors. Both directions under the same progressive resistance. Both sides adapting in proportion. The result is a forearm that doesn't just grip hard — it grips smart. When the flexors hit their limit, the extensors hold. That's the training gap that every other tool leaves open.