"One exercise which helps strengthen the fingers and therefore makes this staccato technique easier to perform is to tap each finger separately as quickly as you can and for as long as you can bear to on any hard surface - a chair arm or table or a friendly knee - and develop the hammer action involved."

RE: I simply have to comment a little on this. Despite the idea of "strengthening the fingers" sounds attractive - in practise it may be rather fruitless.
1)You don't need extra strong fingers at all for playing concertina.
Guitar ( left hand) may be different.
2)It is not so easy to improve individual finger strength as it sounds but it IS possible of course.What you actually may improve a little by the described exercise is coordination of muscle activity but *that* may be more efficiently carried out by suitable pieces of music !
3)There is much misunderstanding that by practise all four fingers may aquire "independencý" and equal abilities. This is anatomically and physiologically not correct. The greatest problem in practise is the fact that 3rd finger ( ring finger) is unevitably dependent on 2nd and 4th. For most people the capabilities of fingers come in this order 1,2,4,3 disregarding that the 4th mostly is handicapped by its shortness ( and sometimes crookedness..)
4)For most people general hand strength is so much more related to everyday work that extra "work-out" may only improve gripping force and that doesn't help for concertina-playing