Learn Hardcore Spanish (Spain): Me duele la espalda cuando muevo la mesa grande.

The thing that hurts (the back) is the subject of doler.
The person who feels the pain is an indirect object, shown by a pronoun (me, te, le, nos, os, les).

So:

Me duele la espalda. – My back hurts.
Te duele la cabeza. – Your head hurts.
Le duelen los pies. – His/her/their feet hurt.

“Mi espalda duele” is grammatically possible, but it sounds unusual and “translated from English”. The natural, everyday way is “Me duele la espalda.”

What exactly does the “me” in “Me duele la espalda” mean? Is it reflexive?

The “me” here is not reflexive; it’s an indirect object pronoun.

Me duele la espalda.
Literally: “The back hurts to me.”

So:

me = to me
te = to you
le = to him/her/you (formal)
nos = to us
os = to you (plural, Spain)
les = to them / to you (plural, Latin America)

It’s the same pattern as with gustar:

Me gusta el café. – I like coffee. (Coffee is pleasing to me.)
Me duele la espalda. – My back hurts. (The back hurts to me.)

Reflexive uses would be things like me lavo (I wash myself), me ducho (I shower), but doler is not reflexive in this sentence.

Why is it “la espalda” with “la”, not “mi espalda” with “mi”?

In Spanish, with parts of the body and clothing, it’s very common to use the definite article (el, la, los, las) instead of a possessive (mi, tu, su) when it’s clear whose body part we’re talking about.

Because we already have me, we know it’s my back:

Me duele la espalda. – My back hurts.
Me lavo las manos. – I wash my hands.
Te peinas el pelo. – You comb your hair.

Using mi espalda is not wrong, but it sounds more marked, like you want to emphasize whose back it is (for contrast, surprise, or clarity):

No, no es tu espalda, es mi espalda la que duele.
No, it’s not your back, it’s my back that hurts.

In neutral sentences, the article is preferred: Me duele la espalda.

Why is it “duele” and not “duelen”? How do I know when to use each form of doler?

The verb doler agrees with what hurts, not with the person.

Duele – when one thing hurts (singular subject)
Duelen – when several things hurt (plural subject)

Examples:

Me duele la espalda. – My back (singular) hurts.
Me duele la cabeza. – My head hurts.
Me duelen las rodillas. – My knees (plural) hurt.
Le duelen los pies. – His/her feet hurt.

In your sentence, the subject is la espalda (singular), so we must use duele.

Could I say “La espalda me duele” instead of “Me duele la espalda”?

Yes, “La espalda me duele” is grammatically correct and understandable, but:

The most common, neutral order is “Me duele la espalda.”
“La espalda me duele” can sound a bit more emphatic or contrastive, like you’re focusing on the back:
- La espalda me duele, pero las piernas no.
  My back hurts, but my legs don’t.

So:

Everyday, default: Me duele la espalda.
For contrast/emphasis: La espalda me duele muchísimo.

Why is it “muevo la mesa grande” and not “muevo a la mesa grande”?

In Spanish, you only use “a” before a direct object when it’s a person (or sometimes a pet you treat like a person). This is the “personal a.”

Muevo la mesa. – I move the table. (no a, it’s an object)
Veo a María. – I see María. (person → needs a)
Ayudo a mi abuela. – I help my grandmother. (person → needs a)

Since mesa is an inanimate object, the direct object is just:

muevo la mesa, not muevo a la mesa.

Why is it “la mesa grande” and not “la grande mesa”?

The usual rule in Spanish is:

Adjectives go after the noun:
- la mesa grande – the big table
- el coche rojo – the red car
- una casa bonita – a pretty house

“La mesa grande” is the completely standard, neutral word order.

Some adjectives can go before or after with a slightly different nuance. For grande:

una mesa grande – a big table (neutral)
una gran mesa – a great / impressive / splendid table (more subjective, often figurative)

So:

la mesa grande = literally a big-sized table.
la gran mesa = “the great table” (more stylistic or emotional, not just physical size).

In everyday speech about furniture size, use mesa grande.

Why do we use the present tense (muevo) after “cuando” in “cuando muevo la mesa grande”? Could it be subjunctive?

In your sentence, cuando introduces a habitual/general situation:

Me duele la espalda cuando muevo la mesa grande.
My back hurts when I move the big table. (in general, whenever I do that)

For habits, general truths, and repeated actions, Spanish uses the present indicative:

Cuando como mucho, me siento mal.
When I eat a lot, I feel bad.
Cuando conduce, escucha música.
When he drives, he listens to music.

You normally use the subjunctive after cuando when you talk about a future action that hasn’t happened yet:

Cuando mueva la mesa grande, me va a doler la espalda.
When I move the big table (later), my back is going to hurt.

So:

General/habitual: cuando muevo (indicative)
Future, not yet realized: cuando mueva (subjunctive)

Can I say “Me duele la espalda al mover la mesa grande” instead of using “cuando muevo”?

Yes, that’s a good and natural alternative:

Me duele la espalda cuando muevo la mesa grande.
Me duele la espalda al mover la mesa grande.

The meaning is very similar: my back hurts when I move the big table.

Difference in form:

cuando + verb (conjugated)
- focuses a bit more on the time/occasion when it happens.
al + infinitive (literally “on/when doing X”)
- slightly more compact and often used in written Spanish or more formal style.

Both are correct and common; you can use either here without changing the basic meaning.

Could I say “cuando estoy moviendo la mesa grande” (present continuous) instead of “cuando muevo la mesa grande”?

You can say it, but there’s a nuance:

cuando muevo la mesa grande
- General/habitual: whenever I move it.
cuando estoy moviendo la mesa grande
- Focuses more on the ongoing action at that moment: while I’m in the process of moving it.

Examples:

Me duele la espalda cuando muevo la mesa grande.
In general, any time I move that table, my back hurts.
Me duele la espalda cuando estoy moviendo la mesa grande.
My back hurts while I’m in the middle of moving the big table (emphasis on the duration of the action).

Both are grammatical. For a simple habitual statement, “cuando muevo…” is more typical.

Is there another way to say “Me duele la espalda”, like using “tener dolor”?

Yes, there are several common ways to express this idea:

Me duele la espalda.
– Most common and natural.
Tengo dolor de espalda.
– I have back pain. (slightly more formal/medical-sounding)
Me he hecho daño en la espalda.
– I’ve hurt my back. (focus on an injury)
Me lastimé la espalda. (more frequent in Latin America than in Spain)
– I hurt my back.

In Spain, for everyday “My back hurts,” “Me duele la espalda” is the standard phrase.
“Tengo dolor de espalda” sounds more like something you’d say to a doctor or in a more formal context.