Using a Camry EH101 electronic hand dynamometer, I went through a few prosthetic terminal devices for my arm to see just how strong they were. And I added a baseline for my (human) left hand and my (bare) stump.
This certainly provides a base for a range of discussions later. Or previous ones ; )
- Human left hand - 47,8 kg
- Bare stump - 16,0 kg
- iLimb grip - 2,2 kg
- Otto Bock myoelectric hand - 13,6 kg
- Hosmer hook with just a few rubbers - 5,2 kg
- TRS Jaws with maximum setting - 5,4 kg
- TRS Jaws XFS with max setting ~ 8,2 kg
- V2P prehensor with a lot of rubbers - 7,0 kg
- TRS Adult Prehensor -- 20,8 kg
- TRS Grip 5 Evolution prehensor - 24,0 kg
- Maker Hand 2020 / 2021 - ~ 0 kg / ~ 1,3 kg / ~ 1,6 kg
Human left hand - 47,8 kg
47,8 kilograms. With that, my left hand never was my dominant hand. It always felt weak. But near 50 kg grip strength is alright. "Ein Zentner" compression makes for a rather hard hand squeeze to put this into context.
Bare stump - 16,0 kg
For some reason I maxed out when pressing 16 kg against this handle there.
iLimb grip - 2,2 kg
We always knew that the iLimb never wanted to hurt anyone ; )
Otto Bock myoelectric hand - 13,6 kg
The Otto Bock myo hand, standard bit of equipment, really has a quite usefully hard squeeze.
Hosmer hook with just a few rubbers - 5,2 kg
While I could throw on more rubbers to make that grip as strong as 8 kg or so, I find that the hook with its shape and an added silicone tube grips perfectly well for all daily situations at just about that type of grip strength.
It can be extremely well dosed, too.
TRS Jaws with maximum setting - 5,4 kg
The TRS Jaws is a device that allows to slide grip strength from a minimal low force to a maximum of about 5,2 to 5,4 kg.
The lock mechanism is somewhat fragile in design so I guess it won't be the type of massive strength gripper other devices can be - such as VC prehensors (see below).
TRS Jaws XFS with max setting ~ 8,2 kg
Update 29.05.2021 - this is a great device with a rugged frame and large grip, helps for heavy boxes and working with tools and machines too.
V2P prehensor with a lot of rubbers - 7,0 kg
The V2P prehensor is a real beauty to tweak, and as that, it provides rather good grip performance. Its soft deformable surfaces add to the 7 kg achieved with these silly office rubbers that I threw on. Just to get an idea.
TRS Adult Prehensor -- 20,8 kg
The TRS prehensor is, as one can see, in a totally different league. Not only is it the easiest device of all of the devices to deliver a minimally dosed amount of grip strength but it also delivers a real lot of it if it has to be.
TRS Grip 5 Evolution prehensor - 24,0 kg
This prehensor follows the same control principle as the TRS adult prehensor but for some reason this test went even higher. I guess I angled out my elbow a bit better. Whatever: the strength that can be applied with this device is quite simply unparalleled.
You have to realize that this technology weighs not much, costs not much, does not use brittle and fragile "high" tech (a misnomer, actually, that mostly describes ill devised electrically motorized devices) and does not cause distracting noise, uses up costly gloves or any of that. No, really, this technology just wants to really perform, blend in, and help you with real stuff.
The thing is, whenever I have stuff to do that is so light that I do not need the prosthetic arm, my stump still performs better than a Hosmer hook or an Otto Bock myoelectric hand - so the old orthopedic surgeons that wrote for unilateral below elbow amputees (you are aware of the title of this website, yes?) that the stump still is better than any prosthesis - for the most part, they were right.
Maker Hand 2020 / 2021 - ~ 0 kg / ~ 1,3 kg / ~ 1,6 kg
While this device has one of the most wicked, insane, clever and intricate, thought out and well designed grip mechanics, raw strength is not its strength. Thus, even catching a heavy plate by its outer margin / angle, the Toughware Equilux with heavily tuned grip pads massively outperforms the Maker Hand. But still, no device reliably grips small things better than this device that also won the 202o Cybathlon prosthetic arm race, as only body powered device, against all other competitors, all of which were myoelectric.