"I have started swimming."
This could mean I have just started moving my arms. Or it could mean that I have enrolled in swimming classes. To my mind one interpretation is a present participle and the other is a gerund. Of course, if I said "I have been swimming" there would be no ambiguity.
"I have started swimming circuits." Is there still ambiguity here? Can 'swimming' be seen as a gerund with 'circuits' as its object?
And what kind of verbal form is 'I have stopped/started/continued running" etc? Is it a form of the progressive, or is the 'ing' form automatically a gerund here? "I have stopped doing that"--is 'doing' a gerund, or are there many forms of the progressive possible that I've never seen explicitly discussed?
Oh, and one more. Sometimes there is more than one meaning that can be derived from the 'ing' form. 'My knitting' could mean 'my action of knitting' or it could mean 'the bundle of linked thread that I have created by performing this action'. Are both meanings gerunds or is the second meaning (which is a physical object) a full noun?