La postura corporal ayuda con la posición abierta.

Because both nouns are feminine singular:

• la postura
• la posición

Also, in Spanish, the definite article is often used to talk about something in a general sense. So La postura corporal can mean body posture in general, not necessarily one specific posture.

English often drops the article in these general statements, but Spanish usually keeps it.

Corporal is the normal adjective meaning bodily / related to the body in this context.

A few useful points:

• postura = noun
• corporal = adjective describing postura
• The adjective corporal goes after the noun, which is very common in Spanish.

Also, corporal has the same form for masculine and feminine in the singular:

• el lenguaje corporal
• la postura corporal

In the plural, it changes to corporales:

• las posturas corporales

Because the subject is La postura corporal, which is singular.

So:

• La postura corporal ayuda = singular subject + singular verb

If the subject were plural, the verb would also be plural:

• Las posturas corporales ayudan

Because it agrees with posición, which is a feminine noun:

• la posición abierta
• not la posición abierto

This is basic adjective agreement in Spanish:

• masculine singular: abierto
• feminine singular: abierta
• masculine plural: abiertos
• feminine plural: abiertas

So abierta matches posición.

They are similar, but not identical.

• postura usually means posture: the way someone holds their body
• posición usually means position: placement, stance, or arrangement

So in this sentence:

• postura corporal refers to body posture
• posición abierta refers to an open position/open stance

A learner might notice that these ideas overlap a lot. That is true. In fact, this sentence sounds a bit unusual because postura and posición are quite close in meaning here.

Yes, and this is a very good question.

Ayudar con means something like:

• to help with
• to help in relation to

So ayuda con la posición abierta is understandable.

But in Spanish, especially in a sentence like this, many speakers would find ayudar a + infinitive more natural. For example:

• La postura corporal ayuda a mantener una posición abierta.
• La postura corporal ayuda a adoptar una posición abierta.

These often sound smoother than ayuda con la posición abierta.

So the original sentence is grammatical enough to understand, but it may not be the most natural way to express the idea.

It is understandable, but many native speakers would probably choose a more natural version.

More natural alternatives might be:

• La postura corporal ayuda a mantener una posición abierta.
• Una buena postura corporal ayuda a adoptar una postura abierta.
• La postura corporal favorece una posición abierta.

Why might the original sound slightly awkward?

1. postura and posición are quite close in meaning here
2. ayuda con is possible, but ayuda a + infinitive often sounds more natural
3. Depending on context, posición abierta may sound a little literal

So yes: understandable, but a bit stiff or translated-sounding.

Because in Spanish, adjectives commonly come after the noun.

So:

• postura corporal
• posición abierta

This is the normal order.

Sometimes adjectives can go before the noun, but that usually changes the tone, emphasis, or meaning. In this sentence, the standard and expected order is noun + adjective.

Yes, but it changes the meaning slightly.

• La postura corporal = body posture in general, or the body posture already being discussed
• Una postura corporal = a body posture / one kind of body posture

If you are making a general statement, la is often more natural:

• La postura corporal influye mucho.

If you mean a certain kind of posture, then una works better:

• Una postura corporal adecuada ayuda mucho.

No, not in normal Spanish.

Spanish usually needs an article here:

• La postura corporal ayuda...

Leaving it out would sound unnatural and incomplete.

English often allows zero article in general statements, but Spanish usually does not.

Here are some natural options, depending on what you want to say:

• La postura corporal ayuda a mantener una posición abierta.
• Una buena postura corporal ayuda a adoptar una postura abierta.
• La postura corporal favorece una postura abierta.
• Mantener una buena postura corporal ayuda a proyectar una posición abierta.

If you want the simplest natural rewrite, a very good choice is:

• La postura corporal ayuda a mantener una posición abierta.

You would need to change the article, noun, and adjective where necessary, and the verb too if the subject becomes plural.

For example:

• Las posturas corporales ayudan con las posiciones abiertas.

But this sounds a bit odd semantically, because people do not often talk about open positions in the plural in this exact way.

A more natural plural example would be:

• Las buenas posturas corporales ayudan a mantener posiciones abiertas.

Notice the changes:

• la → las
• postura → posturas
• corporal → corporales
• ayuda → ayudan
• posición abierta → posiciones abiertas