inserting a character space whilst remaining in normal mode

[Robert Cussons]

Hi all,

something I find myself doing quite often is the above, i.e. I have:
extract(p,f,m,n)

and I want

extract(p, f, m, n)

and rather than going to the comma and pressing 'a', 'space', 'Esc' I 
would prefer to use a single key and stay in normal mode, can someone 
give me a pointer to the place in the help for this, I tried insert, but 
that is all about insert mode.

Many thanks,
Rob.