Learn Hardcore Spanish (Spain): Hoy la espalda está mejor, sin haber dolido tanto como ayer. - Today my back is better, without having hurt as much as yesterday.

In Spanish, body parts are normally referred to with the definite article (el, la, los, las), not with mi / tu / su, when it’s clear whose body part we’re talking about.

So instead of:

mi espalda está mejor – literally “my back is better,”

Spanish usually says:

la espalda está mejor – literally “the back is better,” but understood as “my back is better” if we’re talking about the speaker.

Often, the possessor is shown with a pronoun with the verb, especially with doler:

Me duele la espalda. – My back hurts.
Hoy me duele menos la espalda. – Today my back hurts less.

Mi espalda is not wrong, but it sounds more emphatic or contrastive, or it appears when the possessor might not be obvious from context. In everyday speech in Spain, la espalda is more natural here than mi espalda.

Why is it la espalda (feminine) and not el espalda?

Grammatical gender in Spanish is mostly arbitrary and lexical: you just have to learn the gender together with the noun.

la espalda – the back (feminine)
Not: el espalda

Many, but not all, nouns ending in -a are feminine, and espalda follows that pattern. But remember there are exceptions both ways:

Feminine but not ending in -a: la mano, la noche, la leche
Masculine but ending in -a: el día, el mapa, el problema

So the short answer is: espalda is a feminine noun by dictionary definition.

Why is it está mejor and not es mejor?

This is the classic ser vs. estar distinction.

ser is used for inherent, permanent characteristics.
estar is used for temporary states, conditions, results of change.

Here we’re talking about the current condition of the back today, compared to yesterday. That’s clearly a temporary state, so we use estar:

La espalda está mejor. – The back is better (today / right now).
La espalda es mejor. – would mean something like “the back is better (in general / by nature)”, which doesn’t fit here.

So está mejor is the correct and natural choice.

What exactly is the structure sin haber dolido?

Sin haber dolido is sin (a preposition) + haber dolido (a perfect infinitive).

haber dolido = “to have hurt” / “having hurt”
sin haber dolido = “without having hurt”

This construction is used when:

You need a verb after a preposition (like sin, después de, antes de), and
You want to refer to an action that is completed or viewed as prior to another point in time.

So:

Hoy la espalda está mejor, sin haber dolido tanto como ayer.
≈ “Today the back is better, without having hurt as much as yesterday.”

In grammar terms, haber dolido is a perfect infinitive.

Why is it dolido (past participle) and not doliendo (gerund)?

Because of haber.

haber + past participle forms the compound tenses or the perfect infinitive:
- ha dolido – has hurt
- haber dolido – to have hurt / having hurt

You cannot say haber doliendo. The auxiliary haber must be followed by the past participle, not the gerund.

The gerund form doliendo appears with estar:

Está doliendo. – It is hurting.
Lleva todo el día doliendo. – It’s been hurting all day.

So:

sin haber dolido – correct
sin haber doliendo – incorrect

Could I just say sin doler tanto instead of sin haber dolido tanto? What’s the difference?

Yes, you can say both, but there is a slight nuance:

sin doler tanto como ayer
- Literally: “without hurting as much as yesterday”
- Focuses more on the general, ongoing level of pain during today.
- Very natural and maybe a bit more colloquial.
sin haber dolido tanto como ayer
- Literally: “without having hurt as much as yesterday”
- Emphasises the entire period up to now as something that, overall, did not hurt as much as yesterday.
- Slightly more “complete” or “summary-like” and a bit more formal.

In everyday speech, many natives (in Spain) might more naturally say:

Hoy la espalda está mejor, no ha dolido tanto como ayer.
Hoy la espalda está mejor, ha dolido menos que ayer.

But sin doler tanto and sin haber dolido tanto are both grammatically correct.

Where would I put the pronoun me if I want to say “without having hurt me so much”?

You have two correct options. With infinitives and compound infinitives, the clitic pronoun can go:

Attached to the end of the infinitive:
- sin haberme dolido tanto como ayer
Before the whole infinitive group (but not between haber and dolido):
Actually, with haber + participle as an infinitive, Spanish normally does not place the clitic before haber in this construction after a preposition; the natural version is:
- sin haberme dolido tanto

Forms like sin me haber dolido tanto are incorrect: the pronoun cannot go between sin and haber, nor between haber and dolido.

So the natural version is:

Hoy la espalda está mejor, sin haberme dolido tanto como ayer.

Why is there no me at all in the original sentence, when with doler I usually see things like me duele la espalda?

With doler, the most common pattern is:

(A mí) me duele la espalda. – My back hurts.
(A mí) no me ha dolido tanto la espalda. – My back hasn’t hurt so much.

In your sentence:

Hoy la espalda está mejor, sin haber dolido tanto como ayer.

the verb doler is used a bit impersonally: it just states that “the back hasn’t hurt much,” and the person affected is understood from context (usually the speaker).

In natural conversation, especially in Spain, many speakers would actually prefer to include the me:

Hoy la espalda está mejor, sin haberme dolido tanto como ayer.
Hoy la espalda está mejor; no me ha dolido tanto como ayer.

So: the original sentence is understandable and grammatical, but adding me is more typical in everyday speech because doler almost always involves the experiencer.

Why is it tanto como ayer and not something like tan como ayer or tanto que ayer?

In comparisons, Spanish uses different patterns:

For how much / how many (quantity):
- tanto / tanta / tantos / tantas … como …
- No ha dolido tanto como ayer. – It hasn’t hurt as much as yesterday.
For how + adjective/adverb (quality/degree):
- tan … como …
- No es tan grave como ayer. – It isn’t as serious as yesterday.

So here we’re comparing the amount of pain, a quantity, so we need tanto … como:

tanto como ayer – as much as yesterday

tanto que ayer is not used for this type of comparison; que appears with comparative forms like más que, menos que:

Ha dolido menos que ayer. – It has hurt less than yesterday.
Ha dolido más que ayer. – It has hurt more than yesterday.

Is Hoy la espalda está mejor, sin haber dolido tanto como ayer natural in Spain? How would a Spaniard typically say this?

The sentence is correct and understandable, but for everyday spoken Spanish in Spain, many people would phrase it a bit differently.

More idiomatic options would be:

Hoy la espalda está mejor; no me ha dolido tanto como ayer.
Hoy tengo la espalda mejor; no me ha dolido tanto como ayer.
Hoy me duele menos la espalda que ayer.

Differences:

Adding me makes it sound more natural with doler.
Using no me ha dolido tanto is very common in Spain for “hasn’t hurt so much.”
Hoy me duele menos la espalda que ayer focuses on the current sensation “right now,” whereas the perfect no me ha dolido tanto summarises the whole period up to now.

Your original sentence is more on the careful / written side, especially with sin haber dolido, but it’s fine grammatically.

Can I move hoy to another place in the sentence, like La espalda hoy está mejor or La espalda está mejor hoy?

Yes. Spanish word order is relatively flexible for adverbs like hoy, and all of these are grammatically correct:

Hoy la espalda está mejor.
La espalda hoy está mejor.
La espalda está mejor hoy.

Nuances:

Hoy la espalda está mejor. – Most neutral and common; “Today the back is better.”
La espalda hoy está mejor. – Slightly more focus on la espalda first.
La espalda está mejor hoy. – Can give a bit of extra emphasis to hoy at the end, as a sort of contrast with other days.

But in practice, all three could be used in the same situation without a big meaning difference.