لما بخلص رياضة، بحس ان كتفي بقى مرتاح اكتر.

In Egyptian Arabic, لما usually means when, once, or whenever, depending on context.

Here, because the sentence is describing a usual pattern, لما بخلص رياضة means something like:

• when I finish exercising
• whenever I finish exercising
• once I’m done exercising

It is a very common everyday word in Egyptian speech.

Because the sentence is talking about a general repeated situation, not one single past event.

• بخلص = I finish / I’m finishing in the habitual or non-past sense
• خلصت = I finished for one specific past event

So:

• لما بخلص رياضة... = when/whenever I finish exercising...
• لما خلصت رياضة... = when I finished exercising...

In Egyptian Arabic, بـ- is a very common marker for the present / habitual / ongoing verb.

So:

• بخلص = I finish / I usually finish
• بحس = I feel

This is one of the biggest differences between Egyptian Arabic and Standard Arabic. In everyday Egyptian, the b- prefix is extremely common in present-tense statements.

رياضة in Egyptian can mean:

• exercise
• sport
• working out

In this sentence, it most naturally means exercise or a workout.

Also, it appears without الـ because it is being used in a general sense, like exercise in English.

Here ان introduces the idea after بحس — basically that in English:

• بحس ان... = I feel that...

In careful spelling, you may also see إن, but in informal writing people very often write ان.

In Egyptian pronunciation, it is often said more like inn.

كتفي means my shoulder.

It is made from:

• كتف = shoulder
• -ي = my

So:

• كتف → shoulder
• كتفي → my shoulder

In spoken Egyptian, كتف is often pronounced something like kitf or ketf, so كتفي may sound like kitfi or ketfi.

Here بقى is the verb became / got / has become.

So:

• كتفي بقى مرتاح = my shoulder became more comfortable / my shoulder got relieved

This is different from the very common Egyptian discourse word بقى that can mean things like so, then, now, or add emphasis in conversation.

In this sentence, it is clearly the verb became, because it comes between the subject كتفي and the adjective مرتاح.

مرتاح means comfortable, relieved, or relaxed.

In Egyptian Arabic, it is natural to use it not only for people, but also for body parts or physical feelings. So saying:

• كتفي مرتاح

can mean that your shoulder feels better, more relaxed, or less strained.

It is also in the masculine singular form because كتف is a masculine singular noun.

اكتر means more.

So:

• مرتاح اكتر = more comfortable
• naturally, in English, this may come across as better or more relieved

Egyptian Arabic very often makes comparisons with:

• adjective + اكتر

So this structure is very common and natural.

Because in Egyptian Arabic, adjective + اكتر is a very normal and productive way to express comparison.

So instead of looking for a special built-in comparative form every time, speakers often just say:

• مرتاح اكتر = more comfortable
• تعبان اكتر = more tired
• سهل اكتر = easier / more easy

It is simple and very common in everyday speech.

A rough pronunciation is:

• lamma bakhlaṣ riyāḍa, baḥiss inn كتفي ba’a mertaḥ aktar

A few notes:

• لما = lamma
• بحس is often heard as baḥiss
• ان is often pronounced inn
• بقى here sounds like ba’a
• مرتاح = mertaḥ
• اكتر = aktar

Pronunciation varies a bit by speaker, but that is a good approximation.

Yes, absolutely.

• لما بخلص رياضة = when/whenever I finish exercising
• بعد ما بخلص رياضة = after I finish exercising

Both are natural.
بعد ما is a little more specifically after, while لما is a broader when/once/whenever.

You would normally switch to past forms, for example:

• لما خلصت رياضة، حسيت إن كتفي بقى مرتاح أكتر.

That means you are talking about one actual past occasion:

• When I finished exercising, I felt that my shoulder felt better.

So the original sentence sounds habitual/general, while this version sounds specific and past.