One-handed keyboards - essential ergonomics or encouraging a higher risk technique?

Bigger screens = wider keyboards = more reaching

Recently we've seen a number of one-handed keyboards for smartphones emerge into the market. Ergonomics in action maybe? We explore the pros and cons and set out our concerns about them.

Increased screen size for smartphones seems to be the main driver for one-handed smartphone keyboards - the drift towards 'phablets' (5" to 6.9" screen size). Increased screen size means that with a keyboard spanning across the device, if you are trying to hold and type one-handed, reaching your thumb to the far side of the keyboard is getting harder and harder, and is particularly difficult for people with smaller hands.

Size matters

Device sales figures suggest that tablets may be slipping out of favour, as people move towards bigger screened smartphones. There was also a certain amount of scoffing when Apple recently launched the iPhone SE because it only had a 4-inch screen, which by todays standard is small. In fact the SE is starting to gain reasonable traction in certain markets - possibly driven by its physically more manageable size.

Designers have listened

Designers have taken the general move towards larger screens into consideration – and possibly taken into account the thumb reaching that is necessary even on phones with 4-inch screens or similar 'compact' smartphones. It is good of course that this has been thought about, and the result? One-handed keyboards which shift all the keys into a more reachable area at a bottom corner of the screen (which corner is set by the user depending on whether you are right or left handed).

Rise of the one-handed keyboard

Two examples which we've seen emerge recently are Microsoft's WordFlow keyboard and the Google Keyboard. These provide one-handed layout in different ways. The Word Flow is a curved / arc keyboard which traces the sweep of the thumb across a bottom corner of the screen (see pic below). On larger screened devices the WordFlow also shifts the arc of keys towards the favoured corner thereby eliminating the 'top-far' thumbing position (the maxiumum thumb reach position). In contrast, the Google Keyboard simply compresses the keys together and shifts the whole keyboard to the left or the right – set by the user depending on handedness.
Other popular keyboards which offer one-handed set-ups are Swype and SwiftKey. Some one-handed keyboards are not available yet on iOS but just by searching for one handed keyboard in the app store, there are plenty to choose from besides the ones we've mentioned here – some offer an arc format, some use the sideways compression format.


Since there is such variation in design, and because of the complexity of determining what screen+keyboard+device size combination is optimal for any one person, and in the absence of specific user testing or research it wouldn't be fair to criticize any specific app or design so this blog sets out our broader concerns about using one-handed keyboards.

Usability vs. Ergonomics?

One-handed keyboards seem to be where pure usability and one of the key aims of ergonomics (protecting the human from longer-term discomfort etc.) go slightly separate ways. They are more usable in that some of the keys can be reached more easily on a larger screens, which means they free up the other hand for holding onto abseiling rope, your power-kite or waterskiing handle – great usability, there's no disputes about that! But if a one-handed design encourages people to type with one hand, more often, and for longer periods / longer messages, rather than switching to a two-handed typing technique, in terms of longer-term musculoskeletal risk our view is that's not a positive thing. Research has shown that one-handed or to use the technical term - 'unilateral' - smartphone keyboard use on phones is associated with higher levels of muscle activity in the forearm and thumb muscles and is considered a risk factor for musculoskeletal injury (Xie et al, 2015, Gustaffson, 2011).

The Claw

The main issue is that whatever the keyboard design, one-handed typing will still mean adopting the 'claw' to hold the phone and type at the same time – and this is likely to combined with larger devices. The claw or grip in combination with thumb movements will still put strain on the wrist and thumb. If someone downloads and activates a one-handed keyboard on their phone, it doesn't feel like a stretch to say that they are more likely to use it (rather than keep switching between one-handed and two-handed settings) so effectively these keyboards will encourage one-handed typing. In fairness most if not all of the keyboard apps allow for one-touch switching between one-handed mode and standard mode - it's whether people will actually do that which is debatable.

So really the nub of the question is whether the design changes involved in making the keyboard specifically 'one-handed', counteract the negative effects of potentially increased one-handed typing?

What might the effects be of more tightly packed keys and / or smaller keys on one-handed keyboards

Speed of movement, error rates and time spent texting are all interrelated factors.

In order to counteract the potentially higher error rates on keyboards which have smaller gaps between keys and/or smaller keys (e.g. certain keys on WordFlow in arc mode), users might actually move more slowly to compensate for the need for increased keying accuracy. People with chunkier thumbs in particular are more likely to make key press errors on smaller or more tightly bunched keys, which could mean more time spent correcting, more time holding the device etc.

Fastest texter in the world... does it two-handed

It's worth noting that the worlds official fastest texter, Marcel Fernandez Filho, set the record using a 'standard' layout keyboard in the Fleksy app and he typed using a both-thumbs (bi-lateral!) technique. So although a one-handed keyboard may be more convenient in some circumstances, it is not necessarily going to lead to faster texting.

Pros and Cons - a messy picture

Faster texting movement has been identified as a risk factor for texting injuries (Gustaffson, 2011). Initially it might seem as if slowing things down would surely be a good thing? Possibly, but we also know that when we make more accurate finer movements, we generally maintain a higher static muscle loading for longer, which is a known musculoskeletal risk factor. Then, knocking the ball back to the lower risk side, users' thumb postures at the maxiumum stretch will generally be less severe on a one-handed keyboard.

But are one-handed keyboards smaller than a 'standard' one, and how much is stretching reduced?

We should bear in mind that a compressed keyboard on a larger screened device may be similar in size to a full-size keyboard on – for example – a 4" screen. The diagram below illustrates this – the green area is the same for both device screens. So when an app is said to offer a compressed keyboard, it may not be clear if this offers a design advantage over the size of 'standard' keyboards which we have been using for several years (at least, until the current trend for much larger screened phones began), and which we know have still involved reaches and movements that for some people have resulted in injury. This means that when a one-handed 'compressed' keyboard (which is similar to say a 4" standard keyboard) is combined with a larger device, there are still likely to be musculoskeletal issues in terms of reaching and the grip needed to hold the larger device when using it one-handed.

What about swipe to type? Does that help?

All of these keyboards also offer swipe to type, where you slide your finger (or thumb) from letter to letter rather than tap. This is sometimes referred to as one-handed typing facility but in reality it doesn't change how you hold the device. Your other hand can be kept free whether you are tapping or swiping. Whether or not swiping puts less strain on the thumb and wrists is not something which has been researched to date and the technique of swiping does not suit everyone.

From a personal perspective, swiping does seems to slightly reduce the grip force on the phone, because the more constant thumb pressure can compensates for a reduced grip by the fingers. But that seems to be about it. It also takes a bit of getting used to and not everyone will have the time or inclination!

Summing up

For such an everyday thing as an on-screen keyboard, when we start looking at it, there is a complex combination of factors to bear in mind that could affect the risks to users. Although some of the issues we've raised might seem trivial or marginal, given the number of people using smartphones (hitting the 2,000,000,000 (yep - that's 2 Billion!) this year), statistically there are likely to be a large number of people affected by even marginal changes in risk, if not right now, certainly in the next couple of years as devices are replaced with newer larger screened ones.

Beware the claw
Although some one-handed keyboards may reduce the distance your thumb might have to reach on larger screened devices, they still require repetitive thumb movements combined with 'the claw' to hold your phone. We believe they will also encourage one-handed typing. There is also the unknown effect on the muscles of increased accuracy for keyboards that are compressed and / or have smaller keys.

Illusions of grandeur
Anyone thinking of relying on these as a control measure should consider carefully how much closer and compressed in reality some of the keyboards actually are compared to keyboards we have been used to using for some years, (and which are known to be associated with musculoskeletal symptoms). A positive aspect is that they do give people with smaller hands, the ability to use larger screened devices one-handed without greater discomfort than people with larger hands.

Convenient if one-handed is unavoidable, but avoid prolonged use
Our view is that these keyboards are good for occasional convenience (if you really HAVE to hang onto that windsurf boom while texting your boss!) but in terms of reducing the risks of musculoskeletal injury, we believe for the time being at least they are no substitute for holding your device with one hand and typing using the other, or typing using both thumbs – just like a world record breaker! By setting people up for one-handed typing, they risk validating and encouraging that method of typing, which in our view may still present significant musculoskeletal risks.

Credit where it's due to the designers
People type with one hand – and that's a fact! For example Berolo (2011) found that only 26% of study participants type with both hands, and Hoober (2013) identified 49% of phone use as being one-handed. So given that one-handed use is pretty much inevitable, at least the designers have created keyboards which improve your thumb posture while doing it. All we are saying is – still try to limit how much one-handed typing you do, even on a keyboard which is 'one-handed'.

What would be really clever though is a design concept which is useable, which people like and appreciate, but which also encourages two-handed typing - getting rid of the claw once and for all – like say, a larger screened device… hmmm we seem to have gone full circle! In reality, typing technique is perhaps more of a user-culture issue than a design one.

Possible avenues for research

  • Does swiping to type reduce thumb and wrist strain compared to tapping – on a similar sized keyboard?
  • Does a need for greater accuracy on compressed keyboards lead to greater muscle tension and consequently a higher risk of strain injury?
  • Are one-handed keyboards on larger screened devices significantly more compressed than 'standard' keyboards on smaller devices?


Ewa Gustafsson , Peter W. Johnson , Agneta Lindegård & Mats Hagberg (2011) Technique, muscle activity and kinematic differences in young adults texting on mobile phones. Ergonomics. 54:5, 477-487, DOI: 10.1080/00140139.2011.568634

Yanfei Xie, Grace P.Y. Szetoa, Jie Daia and Pascal Madeleine (2016) A comparison of muscle activity in using touchscreen smartphone among young people with and without chronic neck–shoulder pain. Ergonomics. Volume 59:1. DOI:10.1080/00140139.2015.1056237

Sophia Berolo, Richard P. Wells, , Benjamin C. Amick III (2011) Musculoskeletal symptoms among mobile hand-held device users and their relationship to device use: A preliminary study in a Canadian university population. Applied Ergonomics Volume 42, Issue 2, January 2011, Pages 371–378. Special Section: Ergonomics, health and working time organization.

Hoober, S (2013) How do users really hold their devices? http://www.uxmatters.com/mt/archives/2013/02/how-d...

Target size study for one-handed thumb use on small touchscreen devices. Pekka ParhiAmy K. Karlson, Benjamin B. Bederson. http://research.microsoft.com/pubs/75812/parhi-mobileHCI06.pdf


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