Nem sempre o suor mostra um treino forte.

Nem sempre is the natural Portuguese expression for not always.

In this phrase, nem is part of a fixed expression. Even though não often means not, Portuguese does not normally say não sempre for not always.

So:

• nem sempre = not always
• não sempre = unnatural in normal Portuguese

This is one of those expressions that is best learned as a whole.

Portuguese often uses the definite article where English would not.

So o suor literally looks like the sweat, but in context it can mean sweat in a general sense. Portuguese commonly does this with nouns when talking about something as a concept or general phenomenon.

For example:

• O açúcar faz mal em excesso. = Sugar is bad in excess.
• O suor mostra esforço. = Sweat shows effort.

In English, leaving out the article is more common in general statements. In Portuguese, using o here sounds very natural.

Mostra is from the verb mostrar, which usually means to show.

In this sentence, it has the sense of:

• shows
• indicates
• is evidence of

So o suor mostra um treino forte means something like sweat shows / indicates an intense workout.

It does not necessarily mean a literal visual demonstration only. It can also mean be a sign of.

Portuguese uses the present tense here for a general statement or general truth, just like English does.

So:

• Nem sempre o suor mostra um treino forte.
• Sweat doesn’t always indicate an intense workout.

This is not talking about one specific moment only. It is stating a general idea that is usually true.

Using um makes the phrase sound like an intense workout or a hard workout.

Portuguese often uses the indefinite article in cases where English may or may not use one, depending on style.

So:

• um treino forte = an intense workout
• treino forte can also exist in other contexts, but here um treino forte sounds more complete and natural as the object of mostra

The sentence is saying that sweat does not always point to a hard/intense workout.

Literally, forte often means strong, but in treino forte, it usually means intense, hard, or demanding.

So um treino forte is not really a strong workout in natural English. It is better understood as:

• a hard workout
• an intense workout

This is a good example of a word that is literally close to an English word but often translated differently depending on context.

In Portuguese, adjectives usually come after the noun.

So:

• treino forte = literally workout intense/strong

That is the normal order in Portuguese. English usually puts the adjective before the noun:

• intense workout

Sometimes Portuguese adjectives can come before the noun, but that often changes the tone, style, or meaning. In this sentence, treino forte is the standard order.

Yes. That is also correct.

Both of these are natural:

• Nem sempre o suor mostra um treino forte.
• O suor nem sempre mostra um treino forte.

The difference is mainly emphasis.

• Nem sempre o suor... puts early focus on not always
• O suor nem sempre... starts with the subject, which may sound a bit more neutral

Both mean essentially the same thing.

Portuguese often uses the singular to talk about something in a general, abstract way.

Here:

• o suor = sweat as a general phenomenon
• um treino forte = an intense workout, as a type of thing

English also does this sometimes, but not always in the same way.

A plural version could be possible in another sentence, but it would shift the focus:

• Os suores nem sempre mostram treinos fortes sounds much less natural here

The singular is the most idiomatic choice for this general statement.

Yes, but the structure would change, because suor is a noun and suar is a verb.

• suor = sweat
• suar = to sweat

So the original sentence uses the noun:

• Nem sempre o suor mostra um treino forte.

If you wanted to use the verb, you would need a different construction, for example:

• Nem sempre suar indica um treino forte.

That would mean Sweating does not always indicate an intense workout.

So both ideas are possible, but the grammar is different.

Mostra is natural, but it is not the only option.

Other possible verbs include:

• indica = indicates
• significa = means
• prova = proves (stronger claim)

For example:

• Nem sempre o suor indica um treino forte.
• Nem sempre o suor significa um treino forte.

Each one has a slightly different nuance:

• mostra = shows
• indica = indicates
• significa = means
• prova = proves

In your sentence, mostra sounds natural and easy to understand.