Estira l'esquena i després aixeca la manuella.

They are informal singular imperatives: commands addressed to one person that you would normally say to tu.

• estira = stretch
• aixeca = lift / raise

So the sentence is giving two instructions in sequence.

A useful thing to know is that these forms can also look like the he/she present tense form, but here the context makes it clear that they are commands.

Catalan usually drops subject pronouns when they are not needed, because the verb ending already gives enough information.

So instead of saying:

• Tu estira...

Catalan normally just says:

• Estira...

That is the natural way to give a command. Adding tu is possible, but it usually adds emphasis.

With body parts, Catalan often uses the definite article instead of a possessive adjective when it is obvious whose body part is meant.

So:

• Estira l'esquena naturally means Stretch your back

not Stretch the back in some strange abstract sense.

Using la teva esquena is possible, but it sounds more emphatic or contrastive, like if you were specifically contrasting your back with someone else's.

Because esquena begins with a vowel, the article la is shortened to l' before it.

So:

• la + esquena → l'esquena

This is very common in Catalan:

• l'amic
• l'aigua
• l'esquena

Even though esquena is a feminine noun, the article still becomes l' before a vowel.

després means afterwards, later, or then.

In this sentence, it connects the two actions in order:

1. Estira l'esquena
2. després aixeca la manuella

So it means something like and then.

It is being used here as an adverb on its own.
When Catalan uses després de, that is different: it means after followed by a noun or infinitive.

For example:

• després de dinar = after lunch / after eating

But in your sentence, just després is enough.

manuella is a feminine noun meaning dumbbell.

That is why it takes the feminine article la:

• la manuella

So:

• aixeca la manuella = lift the dumbbell

In fitness contexts, you may also hear other words depending on region or speaker, but manuella is a standard gym-related word.

That is normal in Catalan commands. Imperative sentences typically begin with the verb:

• Estira...
• Aixeca...

This is similar to English:

• Stretch your back
• Lift the dumbbell

So the word order is very natural for instructions, exercises, recipes, and directions.

The sentence you have is for one person, informal.

Other common possibilities are:

• Informal singular: Estira l'esquena i després aixeca la manuella.
• Formal singular: Estiri l'esquena i després aixequi la manuella.
• Informal plural: Estireu l'esquena i després aixequeu la manuella.
• Formal plural: Estirin l'esquena i després aixequin la manuella.

So the version in your sentence is the one you would normally use with tu.

Yes, it can look tricky to an English speaker.

A few useful points:

• In aixeca, the x is pronounced like sh
• So the middle of the word sounds roughly like she
• The word is approximately eye-SHE-ka or, in some accents, closer to uh-SHE-ka

Catalan pronunciation varies by dialect, so you may hear slight differences, but the important thing is that the x here is not like English ks.

Yes. Very naturally, i means and, and després means then / afterwards.

So:

• i després = and then

This is a very common way to link steps in instructions. It shows that the second action happens after the first one.