جهاز المشي في الصالة الرياضية.

Not necessarily. By itself, it is most naturally read as a noun phrase, meaning something like the treadmill in the gym.

There is no verb here, so it is not a complete verbal sentence like The treadmill is in the gym. If you wanted a full sentence in MSA, you could say:

• جهازُ المشي في الصالةِ الرياضيةِ.
  This can function as a simple nominal sentence in context: The treadmill is in the gym.

In Arabic, a sentence like X in Y can work without an explicit word for is in the present tense.

Literally, جهاز means device / machine / apparatus, and المشي means walking.

So:

• جهاز المشي = walking machine/device

This is a very natural Arabic way to name objects: describe what they do rather than use a single unrelated word.

Because this is an iḍāfa construction, often called a possessive or construct phrase.

In an iḍāfa:

• the first noun usually does not take ال
• the second noun can be definite or indefinite
• the whole phrase gets its definiteness from the second noun

So:

• جهاز المشي = the walking device / treadmill
• not الجهاز المشي

Here, المشي is definite, so the whole phrase is definite.

Because in this expression, Arabic treats it as the act/type of walking in a fixed naming pattern.

So جهاز المشي is not just a device for some walking but rather the walking machine, which has become the standard term for treadmill.

This is common in Arabic vocabulary: a noun plus a definite verbal noun or noun becomes the normal name of an object.

في means in.

So:

• في الصالة الرياضية = in the gym

It is a very common preposition in Arabic and is used much like English in.

This is a noun + adjective phrase:

• الصالة = the hall
• الرياضية = sports-related / athletic

Together:

• الصالة الرياضية = the sports hall, which is commonly used for the gym

The adjective الرياضية comes after the noun and describes it.

Because it must agree with الصالة, which is a feminine singular noun.

In Arabic, adjectives agree with the noun in:

• gender
• number
• definiteness

So since الصالة is:

• singular
• feminine
• definite

the adjective must also be:

• singular
• feminine
• definite

That is why you get:

• الصالة الرياضية
• not الصالة الرياضي

Because Arabic adjectives must match the noun in definiteness.

So if the noun is definite:

• الصالة = the hall

then the adjective must also be definite:

• الرياضية = the athletic / sports-related

That gives:

• الصالة الرياضية

If the noun were indefinite, the adjective would also be indefinite.

A simple pronunciation guide is:

• jihāz al-mashy fī aṣ-ṣālah ar-riyāḍiyyah

A few useful notes:

• جهاز = jihāz
• المشي = al-mashy
• في = fī
• الصالة = aṣ-ṣālah
• الرياضية = ar-riyāḍiyyah

The ل in ال changes in pronunciation before sun letters:

• ص in الصالة makes al- sound like aṣ-
• ر in الرياضية makes al- sound like ar-

But in spelling, the ال stays the same.

In Arabic, when ال comes before certain letters, the l sound is assimilated into the next consonant. These are called sun letters.

In this phrase:

• الصالة is pronounced aṣ-ṣālah
• الرياضية is pronounced ar-riyāḍiyyah

But:

• المشي keeps the l sound, because م is a moon letter
• so it is al-mashy, not am-mashy

This affects pronunciation, not spelling.

Because in an iḍāfa phrase, the first noun usually does not take ال, even when the whole phrase is definite.

So:

• جهاز المشي = the treadmill
• not الجهاز المشي

The definiteness of the whole phrase comes from المشي.

This is one of the most important patterns in Arabic grammar.

Yes, literally it is walking device in the gym, but in normal usage جهاز المشي is the standard term for treadmill.

So depending on context, a learner should understand it as:

• the treadmill in the gym

Literal meanings are useful for learning, but the real vocabulary meaning matters more.

In fully vocalized formal MSA, it could be:

• جهازُ المشي في الصالةِ الرياضيةِ

If case endings are being pronounced:

• جهازُ is nominative if it is the topic/subject
• الصالةِ is genitive after في
• الرياضيةِ matches الصالةِ

In everyday reading and most speech, learners usually see and hear it without worrying much about those endings.

No. الصالة الرياضية is a common and clear MSA expression, literally the sports hall.

Depending on region and context, you may also hear other words, such as:

• النادي الرياضي = sports club / gym
• الجيم = gym (borrowed, especially in colloquial speech)

But for Modern Standard Arabic, الصالة الرياضية is a very solid choice.