Learn Hardcore Swahili: Juma anapenda kwenda kituo cha mazoezi baada ya kazi.

a-: the subject prefix for third-person singular (he/she)
-na-: the present-tense (habitual/progressive) marker
penda: the verb root meaning “like” or “love”
Put together, anapenda literally means “he likes” or “he is liking”, with the habitual sense of “he likes (to) …”

Why is the verb following anapenda in the infinitive form kwenda and not in another tense or mood?

After a verb of preference like penda (“to like”), Swahili uses the infinitive (ku- + root) to express “likes to do something.” So anapenda kwenda means “he likes to go.” You do not use the subjunctive (e.g. aende) here, because the structure “likes to [do X]” always requires the infinitive form of the second verb.

What does kituo cha mazoezi literally mean, and why is it used to mean “gym”?

Literally,

kituo means “station” or “center” (a class 7 noun),
cha is the genitive concord “of” for class 7,
mazoezi means “exercises” (a class 6 noun, plural of “zoezi”).
So kituo cha mazoezi = “center of exercises,” which in modern usage is simply “gym” or “training center.”

Why do we use cha (and not ya or la) between kituo and mazoezi?

Swahili links two nouns by matching the genitive concord to the first noun’s class.

kituo is class 7 (ki-),
the genitive concord for class 7 is cha,
even though mazoezi is class 6, you follow the class 7 agreement.
That is why you say kituo cha mazoezi, not kituo ya mazoezi or kituo la mazoezi.

In English we say “go to the gym.” Why isn’t there a preposition like to or kwenye before kituo?

Motion verbs such as kwenda (“to go”) can take a direct noun object in Swahili. You simply say kwenda kituo. (You may also hear kwenda kwenye kituo, with kwenye + noun, but the more straightforward pattern is direct: kwenda soko, kwenda shule, kwenda kituo.)

How is the phrase baada ya kazi constructed, and why is ya used there?

baada is a preposition meaning “after.”
It requires a genitive concord to link to the following noun.
kazi (“work”) is a class 9 noun, whose genitive concord is ya.
Therefore baada ya kazi literally means “after of work,” i.e. “after work.”

Can I say baada ya kukamilisha kazi instead of baada ya kazi?

Yes. After baada ya, you can use any nominalized form, including an infinitive phrase. For example:

baada ya kazi = “after work”
baada ya kukamilisha kazi = “after finishing work”
Both are grammatically correct; the second just specifies the action of completing work.

How would you pluralize kituo cha mazoezi if you wanted to say “gyms”?

You change the class 7 noun kituo to its class 8 plural vituo, and use the class 8 genitive concord vya. The result is:
vituo vya mazoezi = “centers of exercises,” i.e. “gyms.”