Learn Hardcore Spanish (Latin America): Cuando usa patines, mi hermana siempre lleva casco y rodilleras. - When she uses skates, my sister always wears a helmet and knee pads.

usar patines = to use/wear skates (focus on the use of the object)
patinar = to skate (focus on the activity itself)
llevar patines = to have skates on / to be wearing skates (focus on having them on your feet)

So:

Cuando usa patines… = When(ever) she uses skates… (neutral, very natural, especially in Latin America)
Cuando patina… = When(ever) she skates… (a bit more focused on the action, but also very natural)
Cuando lleva patines… = also possible, but a little less usual than usar patines in many areas.

All three are grammatically correct; they just emphasize slightly different aspects.

Why is there no ella in Cuando usa patines? How do we know it means she?

Spanish usually drops subject pronouns because the verb ending already tells you the subject:

usa = 3rd person singular (he, she, it, or you-formal)

Then the rest of the sentence clarifies the reference:

mi hermana (my sister) is clearly she.

So you could say:

Cuando ella usa patines, mi hermana siempre lleva casco y rodilleras.

…but that sounds repetitive (both ella and mi hermana) and a bit unnatural. Native speakers prefer:

Cuando usa patines, mi hermana…

If you only had Cuando usa patines, siempre lleva casco…, the context would decide whether it’s he, she, or you (formal).

Does Cuando usa patines mean when she uses skates or whenever she uses skates?

It can mean both; Spanish present tense with cuando often expresses habitual actions.

Cuando usa patines, mi hermana siempre lleva casco y rodilleras.
This is best understood as:
Whenever she uses skates, my sister always wears a helmet and knee pads.

If you wanted to highlight a single specific occasion, you’d normally add context or use a past tense:

Cuando usó patines ayer, mi hermana llevó casco y rodilleras.
When she used skates yesterday, my sister wore a helmet and knee pads.

Why is there a comma after patines? Is it necessary?

The comma separates a dependent (subordinate) clause from the main clause:

Cuando usa patines, → subordinate clause (condition/time)
mi hermana siempre lleva casco y rodilleras. → main clause

Spanish normally uses a comma when the dependent clause comes first:

Cuando usa patines, mi hermana siempre lleva casco y rodilleras.

If you reverse the order, you usually drop the comma:

Mi hermana siempre lleva casco y rodilleras cuando usa patines.

So the comma is standard and recommended in the original word order.

Can I also say Mi hermana siempre lleva casco y rodilleras cuando usa patines? Is there any difference?

Yes, that version is perfectly correct:

Cuando usa patines, mi hermana siempre lleva casco y rodilleras.
Mi hermana siempre lleva casco y rodilleras cuando usa patines.

Both mean the same. The difference is just emphasis:

Starting with Cuando usa patines highlights the condition/time frame.
Starting with Mi hermana highlights your sister as the topic first.

In everyday speech, both orders are natural.

Why does the sentence use lleva to mean wears? I thought llevar meant to carry.

Llevar is very flexible. It can mean:

to carry / to take
- Llevo la mochila. – I’m carrying the backpack.
to wear (clothes, accessories, protective gear)
- Siempre lleva casco. – She always wears a helmet.
- Llevo jeans y una camiseta. – I’m wearing jeans and a T-shirt.
to have (on you / on your body / in a recipe)
- Llevo gafas. – I wear glasses / I have glasses on.
- Esta salsa lleva tomate. – This sauce has tomato in it.

In the sentence, lleva casco y rodilleras uses the “to wear / to have on” meaning, which is very common in Spanish.

Why is there no article before patines, casco, or rodilleras? Could we say los patines, un casco, las rodilleras?

Yes, you can use articles, but omitting them is very natural here because we’re talking about things in general in a habitual context.

Without articles (as in the original):

Cuando usa patines → when(ever) she uses skates (skates in general)
siempre lleva casco y rodilleras → always wears a helmet and knee pads (protective gear in general)

Possible variants with articles:

Cuando usa los patines, mi hermana siempre lleva casco y rodilleras.
→ Slightly more specific: the skates (maybe a particular pair everyone knows about).
…siempre lleva un casco y rodilleras.
→ Emphasizes “a helmet” (one helmet) rather than the concept of helmet-wearing in general.
…siempre lleva el casco y las rodilleras.
→ Sounds like specific, known items: the helmet and the knee pads (that we both know about).

So:

No article = more generic, habitual.
Articles = more specific/particular items.

What exactly does patines mean? Is it roller skates, inline skates, or just “skates”?

Patines literally means skates and can cover:

ice skates → patines de hielo
roller skates (2×2 wheels) → patines or more specifically patines de cuatro ruedas
inline skates → patines en línea

In many real-life contexts, patines by itself (especially for kids and casual talk) often refers to roller or inline skates, and the specific type is clear from context.

Related words:

patinar → to skate
patineta (LA) → skateboard; also used in some areas for a small scooter
monopatín (more common in Spain) → skateboard

Why is rodilleras plural? Could you say rodillera?

Rodilla = knee.
Rodillera = a knee pad (one), but in practice they are almost always used in pairs.

So:

rodilleras = knee pads (plural), normally one for each knee.

You can say rodillera (singular) if you really mean just one:

Lleva una rodillera en la rodilla derecha.
She wears a knee brace/pad on her right knee.

But for normal protective gear, people usually say rodilleras (plural), just like English normally says knee pads.

If mi hermana is feminine, why don’t the verbs usa and lleva change form?

Spanish verb endings change for person and number (I/you/he-she/we/they), but not for gender.

usa = he uses / she uses / you (formal) use
lleva = he wears / she wears / you (formal) wear

Gender shows up in:

nouns: hermano (brother) vs hermana (sister)
adjectives: alto (tall, masc.) vs alta (tall, fem.)
some articles/determiners: el vs la, los vs las

So:

mi hermana (feminine noun)
usa / lleva (same form for both he and she)

If you added an adjective, you’d see the gender agreement:

Mi hermana siempre lleva casco y rodilleras y está muy preocupada por su seguridad.
(preocupada matches the feminine hermana.)

Can I move siempre? For example: mi hermana lleva siempre casco y rodilleras?

Yes. Common options:

Mi hermana siempre lleva casco y rodilleras.
Mi hermana lleva siempre casco y rodilleras.

Both mean My sister always wears a helmet and knee pads.

Differences:

Siempre lleva (adverb before the verb) is the default, most neutral order.
Lleva siempre is also correct and common; it can sound slightly more emphatic or stylistic in some contexts, but usually the difference is minimal.

You generally do not put siempre at the very end:

❌ Mi hermana lleva casco y rodilleras siempre.
This is understandable but can sound awkward or heavily stressed in many contexts.

Could I say Cuando patina, mi hermana siempre lleva casco y rodilleras instead of Cuando usa patines…?

Yes, that’s perfectly correct:

Cuando patina, mi hermana siempre lleva casco y rodilleras.

Nuance:

Cuando usa patines → focuses slightly more on the use/wearing of the skates as equipment.
Cuando patina → focuses on the action: when she skates.

In normal conversation, both would be understood the same way and both sound natural.

How would this sentence change if I were talking politely to usted instead of mi hermana?

For usted (formal you), the verb forms are the same as for él/ella, but you’d use the pronoun usted or a formal noun phrase instead of mi hermana.

Examples:

Cuando usa patines, usted siempre lleva casco y rodilleras.
When(ever) you use skates, you always wear a helmet and knee pads.

Or, to avoid ambiguity (making sure it’s clearly “you”):

Cuando usted usa patines, siempre lleva casco y rodilleras.

Structure is the same; only the subject changes.