Bila saya menaiki tangga, siku dan lutut saya masih terasa lemah.

Here, bila means when.

So Bila saya menaiki tangga means When I climb/go up the stairs.

A useful note:

• bila can also be a question word meaning when?
• In this sentence, it is not a question. It is a conjunction meaning when.
• More formal alternatives are apabila or ketika.

Menaiki comes from the root naik.

• naik = to go up, rise, climb
• menaiki = to go up/climb something

The ending -i and the prefix meN- make the verb work more clearly with an object:

• menaiki tangga = climb the stairs / go up the stairs

In everyday Malay, naik tangga is also very common and natural.
So both can work, but menaiki tangga sounds a bit more explicit or slightly more formal.

It can mean either stairs/staircase or ladder, depending on context.

In this sentence, menaiki tangga is most naturally understood as going up the stairs.

If the context were about housework or construction, tangga could also mean ladder.

In Malay, possession usually comes after the noun.

So:

• siku saya = my elbow
• lutut saya = my knee

When two nouns are joined together, one saya at the end can apply to both:

• siku dan lutut saya = my elbows and knees

You could also say:

• siku saya dan lutut saya

But the version in the sentence is more compact and natural.

Malay often does not mark plurals if the meaning is already clear from context.

So:

• siku can mean elbow or elbows
• lutut can mean knee or knees
• tangga can mean stairs without any extra plural marker

The listener understands from meaning and real-world logic.

Malay can show plural with reduplication, but it is not needed here:

• lutut-lutut
• siku-siku

That would sound unnecessary in this sentence.

Masih means still.

So:

• masih terasa lemah = still feels weak / still feel weak

It shows that the weakness continues and has not gone away yet.

Without masih, the sentence would simply state that the elbows and knees feel weak.
With masih, it emphasizes continuation.

Terasa means something like feels, can be felt, or is felt.

In this sentence:

• siku dan lutut saya masih terasa lemah = my elbows and knees still feel weak

Compared with plain rasa, terasa often suggests a sensation that is noticed or experienced, sometimes a little more involuntarily.

Compare:

• Saya rasa lemah = I feel weak
• Lutut saya terasa lemah = My knees feel weak

So terasa fits well when talking about a body sensation.

Malay often does not need a verb like to be in the same way English does.

English says:

• My elbows and knees are weak
• My elbows and knees feel weak

Malay can simply use:

• siku dan lutut saya lemah = my elbows and knees are weak
• siku dan lutut saya terasa lemah = my elbows and knees feel weak

So there is no missing word here. The sentence is complete as it is.

Malay verbs do not change form for tense the way English verbs do.

So menaiki does not itself mean specifically:

• climbed
• climb
• will climb

The time is understood from context.

In this sentence, bila makes it sound like:

• when I climb the stairs
• when I go up the stairs
• possibly whenever I climb the stairs

If you wanted to make time clearer, you could add words such as:

• semalam = yesterday
• sekarang = now
• esok = tomorrow
• sedang = in the middle of doing
• akan = will

Yes. Malay word order is fairly flexible in sentences like this.

You could also say:

• Siku dan lutut saya masih terasa lemah bila saya menaiki tangga.

This means basically the same thing.

The difference is mainly focus:

• Bila saya menaiki tangga, ... puts the time/situation first
• Siku dan lutut saya masih terasa lemah ... puts the body parts and the feeling first

Both are natural.

Yes, siku does mean elbow.

And yes, a native English speaker may find elbows feel weak a bit less common than expressions like:

• my arms feel weak
• my joints feel weak
• my knees feel weak

But grammatically, the Malay sentence is fine. It is just being specific about body parts.

If the intended meaning were more general, other words might be used depending on context:

• tangan = hand/arm
• kaki = leg/foot
• sendi = joint

So the original sentence is correct, but English learners may notice that the body-part choice feels a little more specific than typical English phrasing.