O desporto ajuda a manter o corpo saudável.

In European Portuguese, the usual word is desporto.

In Brazilian Portuguese, the more common word is esporte.

So for Portugal, O desporto is the natural choice. Both words refer to sport, but desporto is the standard form you should learn for Portuguese from Portugal.

Portuguese often uses the definite article with nouns when speaking about something in general.

So:

• O desporto ajuda... = Sport helps...
• A música é importante. = Music is important.
• O exercício faz bem. = Exercise is good for you.

In English, we often leave the article out in these general statements, but Portuguese usually keeps it.

Here it means sport in general.

Even though desporto is singular, Portuguese often uses the singular form with the article to talk about a whole category or activity in a general sense.

So O desporto ajuda... means something like Sport / doing sport helps..., not that one particular sport.

After ajudar, Portuguese often uses a + infinitive.

So:

• ajudar a manter = to help to keep
• ajudar a estudar = to help to study
• ajudar a melhorar = to help to improve

This a is very common in Portuguese from Portugal. In English, we just use to, but in Portuguese the structure is built into the grammar: ajudar a + infinitive.

In standard European Portuguese, ajuda a manter is the normal and safest form.

You may sometimes see ajudar + infinitive in other varieties or contexts, but for Portuguese from Portugal, learners should usually use:

• ajudar a fazer
• ajudar a compreender
• ajudar a manter

So in this sentence, ajuda a manter is the best choice.

Manter means to keep or to maintain.

In this sentence, it means:

• manter o corpo saudável = to keep the body healthy

It is not reflexive here, and it does not mean to hold in a physical sense. It means to preserve a condition.

A few similar examples:

• manter a casa limpa = to keep the house clean
• manter a calma = to keep calm
• manter o corpo saudável = to keep the body healthy

Because saudável is describing the body, not the way the action is done.

Compare:

• manter o corpo saudável = keep the body healthy
  Here, saudável is an adjective describing corpo.

• viver saudavelmente = live healthily
  Here, saudavelmente is an adverb describing how someone lives.

So after manter, Portuguese often uses:

manter + noun + adjective

Examples:

• manter a mente ativa = keep the mind active
• manter a porta fechada = keep the door closed
• manter o corpo saudável = keep the body healthy

Yes, saudável agrees with corpo, which is singular and masculine.

The reason it does not seem to change is that saudável has the same form in the singular masculine and singular feminine:

• corpo saudável = masculine singular
• vida saudável = feminine singular

But in the plural, it changes:

• corpos saudáveis
• vidas saudáveis

So agreement is happening, but the singular form looks the same for both genders.

Here o corpo means the body in a general, typical sense.

Portuguese often uses the definite article in places where English may sound more general or abstract. So:

• manter o corpo saudável sounds natural in Portuguese
• English may say keep the body healthy or sometimes just keep healthy, depending on style

Using o corpo makes the sentence sound complete and natural.

Not in normal modern Portuguese.

The natural structure here is:

manter + object + adjective

So:

• manter o corpo saudável = natural
• manter saudável o corpo = possible only in marked, poetic, or unusual style
• saudável o corpo = not natural here

Portuguese usually places the adjective after the noun in this kind of structure, especially after verbs like manter, deixar, and tornar.

Yes, but the meaning changes slightly.

• desporto = sport, often suggesting sports activities in general
• exercício = exercise, usually more directly connected with physical activity for fitness or health

So:

• O desporto ajuda a manter o corpo saudável.
• O exercício ajuda a manter o corpo saudável.

Both are correct, but desporto sounds more like sport, while exercício sounds more like exercise.

Yes, it is natural and grammatically correct.

It has several very typical features of European Portuguese:

• definite article with a general noun: O desporto
• ajudar a + infinitive: ajuda a manter
• manter + noun + adjective: manter o corpo saudável

So it is a good model sentence for learners.