Hi uchiha_yuki, the verb 'swim' is irregular so you would need to say 'I have swum recently' and although this is grammatically correct (because it’s ok to use the present perfect with a non specific time expression such as ‘recently’), but the change of aspect changes the emphasis. The present perfect continuous/progressive (I have been swimming) implies duration and sounds like you've been to the pool several times (and as Gloria, says, it sounds like you plan to continue), whereas the present perfect simple (I have swum recently) focuses on ‘an experience’ so it sounds like you did it once (recently). Hope this helps.

You can say it that way; 'I've swimmed a lot recently'. Everyone will know exactly what you mean even though your English is flawed. However, if you write your English that way, the errors in your written English will be made immediately evident. Don't complicate everything. Keep it simple. .

To me "have been swimming" implies that you will probably swim today or tomorrow or one of these days again. If you have no intention of continuing the activity, you'll probably say "I swam a lot" and that is that, no more swimming. "have swam" seems to mean some definite result of your activities without the continuation. I just can't imagine the situation where it would be appropriate.

The past tense of "swim" is "swam", not "swimmed"! "Swimmed" isn't even a word in English! If you "have been" doing something, it implies that you "were doing/are still doing" it.