Learn Hardcore Swahili: Ndiyo maana mimi nimekuwa nikijaribu kufanya mazoezi mwenyewe nyumbani. - That’s why I have been trying to do exercises by myself at home.

You might see it also written as Ndio maana (without y). In everyday writing they are treated the same; ndiyo is a bit more careful/older spelling, but the meaning and usage are the same here.

Why do we need mimi if the verb already has ni- to show “I”?

The ni- at the start of nimekuwa already marks the subject I. So grammatically, Mimi is not required.

Mimi is added for emphasis or contrast, for example:

Ndiyo maana mimi nimekuwa nikijaribu...
= That’s why I, (as opposed to others), have been trying...

If you remove it:

Ndiyo maana nimekuwa nikijaribu kufanya mazoezi mwenyewe nyumbani.
This is still perfectly correct; it just sounds a bit less emphatic.

So mimi here is like stressing I in English: That’s why I have been trying…

What tense or aspect is nimekuwa nikijaribu, and what nuance does it have?

Nimekuwa nikijaribu is a combination that corresponds closely to English “I have been trying”.

Structure:

nimekuwa = ni- (I) + -me- (perfect) + kuwa (to be)
→ I have been / I have become
nikijaribu = ni- (I) + -ki-jaribu (trying / while trying – an ongoing or background action)

Together, nimekuwa nikijaribu describes an action that started in the past and has been ongoing or repeated up to now.

Nuance:

Ongoing, possibly over a period: I have been trying (for some time)
Often suggests effort or repeated attempts, not just a single try.

Why is it nikijaribu and not najaribu or nimejaribu?

These forms give different aspects:

najaribu (or ninajaribu)
→ I am trying (right now, present progressive).
nimejaribu
→ I have tried (completed attempts; result-focused).
nikijaribu
→ ni-
- -ki-jaribu: trying in an ongoing / background way.
  On its own it often means while I am trying / when I am trying, but when combined with nimekuwa:
- nimekuwa nikijaribu
  = I have been trying (ongoing over time).

If you said:

Ndiyo maana najaribu kufanya mazoezi...
→ That’s why I am trying to exercise (now).
Ndiyo maana nimejaribu kufanya mazoezi...
→ That’s why I have tried to exercise (I have made attempts).
Ndiyo maana nimekuwa nikijaribu kufanya mazoezi...
→ That’s why I have been trying to exercise (for some time, repeatedly).

So the original sentence uses nimekuwa nikijaribu to highlight the ongoing, repeated nature of the trying.

How does kujaribu work with another verb, like kufanya in nikijaribu kufanya mazoezi?

In Swahili, when one verb means try / want / begin / manage etc., and it is followed by another verb, the second verb usually stays in the infinitive form with ku-.

Pattern:
[verb] + ku-verb

Examples:

najaribu kusoma = I am trying to read
alijaribu kuimba = he/she tried to sing
nimekuwa nikijaribu kufanya mazoezi = I have been trying to exercise

So kujaribu kufanya is to try to do. The ku- on fanya is needed here because it is the verb that depends on kujaribu.

What exactly does mazoezi mean, and why is it plural?

Mazoezi comes from the root -zoe- (to get used to, to practice).

zoezi = an exercise / a practice (singular)
mazoezi = exercises, practice, training (plural noun class 6)

In everyday Swahili, mazoezi is used almost like an uncountable noun:

kufanya mazoezi = to do exercise / to work out / to train

You will usually say kufanya mazoezi for to exercise, not kufanya zoezi (unless you really mean a single specific exercise, like one question or one drill).

What does mwenyewe add to the sentence, and how is it different from peke yangu?

Mwenyewe is a reflexive/emphatic word roughly meaning oneself / by oneself / on one’s own.

mimi mwenyewe = myself / I myself
In the sentence:
...kufanya mazoezi mwenyewe nyumbani.
→ to exercise by myself / on my own at home.

Peke yangu also means by myself, but there is a subtle difference:

mwenyewe = emphasises self / independence / doing it yourself
peke yangu = emphasises being alone, with no one else

Often both can be used:

kufanya mazoezi mwenyewe nyumbani
kufanya mazoezi nyumbani peke yangu

Both can translate as to exercise by myself at home, but:

mwenyewe leans toward I’m doing it myself (not with help).
peke yangu leans toward I’m alone when I do it.

Why is there no word like “at” before nyumbani?

In Swahili, many location meanings are expressed with the -ni ending, not with a separate preposition.

nyumba = house
nyumbani = at home / in the house

So nyumbani already means at home, and you do not need an extra preposition:

nipo nyumbani = I am at home
kufanya mazoezi nyumbani = to exercise at home

This happens with other location nouns too:

shule → shuleni = at school
kanisa → kanisani = at church

Could the word order be different, for example putting nyumbani earlier?

Swahili word order is fairly flexible for adverbs and location phrases, but some positions are more common or natural.

Your sentence:

...kufanya mazoezi mwenyewe nyumbani.
(exercise by myself at home)
This is very natural.

You could also say, for example:

...kufanya mazoezi nyumbani mwenyewe.
This is still understandable, but now nyumbani comes earlier; it slightly shifts the focus to at home first, then by myself.

Putting nyumbani much earlier, like:

Ndiyo maana nyumbani nimekuwa nikijaribu kufanya mazoezi mwenyewe.

is possible in context (maybe contrasting home vs gym), but it sounds more marked and needs the right context to feel natural. The original order is the most neutral.

Is there a simpler or more everyday way to say the same thing?

Yes. Nimekuwa nikijaribu is perfectly correct and natural, but if you want something simpler, you could say, for example:

Ndiyo maana najaribu kufanya mazoezi mwenyewe nyumbani.
→ That’s why I’m trying to exercise by myself at home.

This uses najaribu (present progressive) instead of the more complex nimekuwa nikijaribu (present perfect progressive). The meaning is close; you just lose some of the ongoing / for some time nuance.