Peer-reviewed epidemiological and clinical research on pianists using the conventional keyboard  shows a link between small hand spans and pain and injury.

Recent studies in the US which compare performance and health outcomes for pianists using keyboards of different sizes support this evidence. A pianist moving to narrower keys is, in effect, getting ‘larger hands’.

Female pianists run a much greater risk – approximately 50% higher – of pain and injury than males. Some studies have found that  70-80% of female pianists are affected by playing-related pain or injury at some stage during their lives.

Children and teenagers have also been found to suffer from pain and injury related to piano playing. Piano teachers have a duty of care in this regard – a mismatch between hand size and the repertoire taught can be a factor.

See also: http://smallpianokeyboards.org/pain-injury-and-performance-quality/