الدراجة الثابتة قرب جهاز المشي.

In Arabic, the present-tense to be is usually omitted in simple statements.

So Arabic says:

الدراجة الثابتة قرب جهاز المشي.

where English would say:

The stationary bike is near the treadmill.

This is completely normal in Modern Standard Arabic.
If you wanted was or will be, then Arabic would usually use a verb such as كان or سيكون.

Because in Arabic, adjectives normally come after the noun they describe.

So:

• الدراجة الثابتة = the stationary bike
• literally: the bike stationary

This is the normal Arabic word order for noun + adjective.

Because Arabic adjectives agree with the nouns they describe in definiteness.

So if the noun is definite:

• الدراجة = the bike

then the adjective must also be definite:

• الثابتة = the stationary

Together:

• الدراجة الثابتة = the stationary bike

If it were indefinite, both words would usually be indefinite:

• دراجة ثابتة = a stationary bike

Because دراجة is a feminine noun, so the adjective has to be feminine too.

• masculine: ثابت
• feminine: ثابتة

Arabic adjectives agree with the noun in gender, as well as in definiteness and usually number/case.

So:

• دراجة ثابتة
• الدراجة الثابتة

are correct because دراجة is feminine.

Functionally, yes, you can understand قرب here as meaning near.

So:

• قرب جهاز المشي = near the treadmill

Grammatically, قرب is often treated more like a noun/adverbial expression of place than a simple preposition. In fully formal grammar, it behaves a bit like the vicinity of, and the following noun comes after it in a genitive relationship.

But for a learner, the easiest way to understand it is:

• قرب = near

Because جهاز المشي is an iḍāfa construction, often called a possessive or noun-noun construction.

Literally, it is something like:

• جهاز = device/machine
• المشي = walking

So:

• جهاز المشي = the walking device / treadmill

In an iḍāfa:

1. the first noun usually does not take الـ
2. the second noun can be definite
3. the whole phrase gets its definiteness from the second noun

So جهاز المشي is correct, while الجهاز المشي is not the normal structure here.

Yes, المشي literally means the walking or walking as a verbal noun.

In جهاز المشي, Arabic is using a common pattern where a thing is named through an iḍāfa:

• جهاز = device
• المشي = walking

Together it means the machine associated with walking, i.e. treadmill.

So yes, there is a literal sense of device of walking, even though in natural English we just say treadmill.

With full case endings, it would be:

الدَّرَّاجَةُ الثَّابِتَةُ قُرْبَ جِهَازِ الْمَشْيِ.

Here is why:

• الدراجةُ: nominative, because it is the subject/topic of the sentence
• الثابتةُ: nominative, because it agrees with الدراجة
• قربَ: accusative as an adverbial expression of place
• جهازِ: genitive after قرب in this structure
• المشيِ: genitive because it is the second term of the iḍāfa

In normal unvoweled Arabic writing, these endings are usually not written.

The ل of الـ is not always pronounced. It depends on the next letter.

In this sentence:

• الدراجة → pronounced ad-darrāja
• الثابتة → pronounced ath-thābita
• المشي → pronounced al-mashy

Why?

Because:

• د and ث are sun letters, so the l sound of الـ assimilates to the next consonant
• م is a moon letter, so the l is pronounced normally

So the beginning sounds are:

• ad-
• ath-
• al-

not al-d..., al-th..., al-m... for all three.

Yes. That is also natural.

So you could say:

الدراجة الثابتة بالقرب من جهاز المشي.

This also means The stationary bike is near the treadmill.

A rough comparison:

• قرب جهاز المشي = near the treadmill
• بالقرب من جهاز المشي = close to / near the treadmill

The version with بالقرب من is a little more explicitly prepositional and may feel slightly fuller, while قرب is shorter and compact.

It becomes indefinite.

• الدراجة الثابتة = the stationary bike
• دراجة ثابتة = a stationary bike

So the meaning changes from a specific, known bike to an unspecified one.

This is an important pattern in Arabic:

• definite noun + definite adjective
• indefinite noun + indefinite adjective

The adjective matches the noun.