Thumb Keys

I wrote recently about putting modifiers on your home-row keys for better ergonomics. There’s another significant improvement that can be made, before taking the ultimate step of switching to a non-QWERTY layout and re-learning how to type, which is something that most of us will probably never do.

Many ergonomic mechanical keyboards these days, and split keyboards in particular, are designed with the thumbs in mind. Thumbs are our strongest digits, but on most conventional keyboards their responsibility is largely confined to the Space key. I’m a right-thumb spacer, and my left thumb tends to only touch the left Command modifier key. That’s not just a huge waste of the power of the thumbs, but it’s also an ergonomic risk because proportionately more keypresses fall under the purview of the other, weaker digits on each hand.

A particular problem exists with whitespacing keys. Backspace and Return are both likely to be pressed by the right pinkie finger, which is the weakest finger of that hand. The same problem exists for Tab and Escape on the left hand, and of course for both of the Shift keys. There’s a significant opportunity to offload those often-needed keystrokes onto the underused thumbs, given suitable physical keys for the task.

Here’s my own setup, on a split keyboard called the Voyager, which has two thumb keys per hand.

The shaded keys are where my fingers rest in home position. For the keys with two different glyphs, the upper one (in blue) is the key’s function when held, rather than when tapped. If you’re unfamiliar with any of those glyphs, the hold-functions on the alphabetic keys are the standard modifiers used on Apple devices: from left on keys ASDF, they are Shift, Control, Option, and Command. The hold-function glyphs on the two home-position thumb keys indicate that they switch to other layers on the keyboard.

First, and most importantly, I have my Space (␣) key where my right thumb expects it to be, on my right home key within the thumb cluster, and I have the other whitespacing key I most often need — the Return (⏎) key — on the corresponding left thumb’s home key.

This setup means that the maximum deviation I ever need to make while I’m in the flow of typing will be one diagonal unit, for my forefingers to reach the TYBN keys. Everything else is within one vertical unit of deviation (a physically easier motion), or one horizontal unit for G and H — and it’s worth noting that the largest movements are reserved for the strongest and most flexible fingers, as they ought to be.

The hold functions of the two thumb-home keys are for layer-switching, providing access to three further layers when held; one layer for each of those keys, plus a tertiary layer when both are held together. Having layer-switching on home-position keys is a solid strategy, again due to finger strength and thus stability. It also helps to make the other layers feel very accessible, since no finger deviation at all is needed to reach them.

This is quite a conventional configuration for a thumb cluster. It becomes a little more subjective when we consider the secondary thumb keys. These are reached via one unit of thumb-extension, i.e. reaching the thumbs horizontally towards the midpoint of the keyboard’s overall area.

As an aside, it’s useful to realise that a horizontal thumb movement towards the centre of the keyboard is an extension, just like moving a (non-thumb) finger vertically upwards or away from the body. Conversely, a thumb movement horizontally towards the outer sides of the keyboard is a contraction, like curling a finger downwards or towards the body. This is of course just due to the unique anatomy and axis of the thumb versus the fingers. A thumb-cluster of keys is thus functionally vertical or columnar, even though it is physically horizontal (or approximately so). The keys within a given hand’s thumb cluster are as ergonomically mutually exclusive for the corresponding thumb as the keys in a single column of the keyboard are for the corresponding finger.

Let’s get a close-up of those thumb keys.

Using a computer involves much more than just typing, and the modifier keys help to trigger all kinds of functions on every operating system. I have home row modifiers on both halves of the keyboard, but for capitalisation it’s usually easier to have a dedicated Shift key elsewhere — and there’s no better place than under a strong thumb. The secondary thumb keys are excellent places for the two most-needed modifier keys, and one of those is always Shift. The other one depends on your operating system and perhaps on your type of work; for me, using an iPad, it’s the Command key.

As I mentioned earlier, I always pressed the Command key on traditional keyboards with my left thumb, so it was easy to decide to put it on the left secondary thumb key, making use of decades of muscle memory. Conversely, I tended to use whichever Shift key was closest to the key I’d be pairing it with, so I wasn’t losing anything by having my thumb-cluster’s Shift key on the right hand.

The interesting matter is the possible tap (rather than hold) functions of those two secondary thumb keys. Modifiers are only useful when held, and there’s no need to waste a whole physical key for just a hold function — that’s the point of home row mods, after all — so there’s an opportunity to have one or two additional functions assigned to the powerful, flexible thumbs.

Though I wish it was otherwise, I do still need the backspace (⌫) key fairly often. Granted, it’s mostly for rephrasing and other editing, rather than miskeying very much — though there’s always an adjustment period of increased errors after modifying a keyboard layout, which I do more often than most people. Backspace also functions as delete for highlighted interface items and so on, so it pays to keep it close by.

Its conventional position at the extreme top-right of the primary block is almost comically unreachable from an ergonomic perspective; my own style of hitting it was with a whole-hand lift, and then cobra-striking it with my right middle finger. Repositioning a hand is a sure-fire path towards errors, and of course slowdown, so it’s a breath of fresh air to have backspace under my thumb instead.

My choice of putting it on the right secondary thumb key instead of the left was made for two reasons: firstly because backspace is on the right side of the keyboard anyway, so the hand-association was already ingrained, and secondly because it made sense to put functionally-exclusive keys like space and backspace on the same hand, since I’ll never use them simultaneously.

I haven’t added a tap function to the left hand’s secondary thumb key, leaving it as a dedicated Command modifier hold-function key for now. It’s not uncommon, though, to have Tab in a thumb cluster, and it could be very useful if — for example — you’re in the habit of manually indenting code, or using app-switching or window-tab-switching keyboard shortcuts very often. As always, the choice is yours, and you should make it after due consideration.

I won’t pretend that it’s a seamless adaption. When you first use a thumb cluster, if you also move your whitespacing keys down there, then you’re going to feel like you’re learning to juggle for the first hour or so. But you’ll adapt, and before you know it you’ll discover the delightful feeling of being able to take new paragraphs, correct errors, and even confirm or dismiss UI prompts without moving your hands away from home position at all, and indeed with only a single unit of thumb-extension at most.

Ergonomics isn’t about dry metrics like units of extension or contraction, though; it’s about how it feels, or actually how you’ll feel after years and years of wear and tear on joints, muscles, and tendons which evolved for very different tasks than they’re now being asked to perform.

The toughest change you can make to your keyboard is switching to a base layout other than QWERTY, or whichever one you’re used to. That’ll take months. The next toughest change is probably getting used to a split board — unless you’ve always followed touch-typing technique precisely, without ever cheating by borrowing a hand from the other half of the keyboard. Otherwise, it’ll take weeks.

Then we get into the much easier adaptions, which can be made in the order of a handful of days. Home row mods are a prime example. And finally, we get to the easy stuff that you can probably get used to after a few hours — and a thumb cluster, even with whitespacing keys, falls into that category.

When you consider the degree of contortion involved in making the corresponding movements on a conventional keyboard, I think it’s more than worth the effort to protect yourself from pain and incapacity in future.