Schiena vs. dorso
Both schiena and dorso translate to the English word back, but they are used in different contexts. The word schiena is the common, everyday term used almost exclusively for the human back. In contrast, dorso is a more formal or anatomical term, typically used to describe the back of animals, the back surface of objects, or specific athletic terms.
Schiena
The word schiena is the most common and colloquial way to refer to the human back, extending from the neck to the pelvis. It is widely used in everyday conversations to talk about back pain, human physical posture, carrying things, and in common idioms.
Mi fa male la schiena da ieri a causa del sollevamento pesi.
(My back has been hurting since yesterday because of weightlifting.)
Non voltare mai la schiena ai tuoi amici quando hanno bisogno di te.
(Never turn your back on your friends when they need you.)
Il bambino si è addormentato felicemente sulla schiena di suo padre.
(The child fell asleep happily on his father's back.)
Dormire sulla schiena può aiutare a prevenire i dolori muscolari.
(Sleeping on your back can help prevent muscle aches.)
Ieri ha portato uno zaino pesantissimo sulla schiena per tutto il viaggio.
(Yesterday he carried a very heavy backpack on his back for the whole trip.)
Quell'uomo ha lavorato duramente in fabbrica e si è spezzato la schiena.
(That man worked hard in the factory and broke his back.)
Dorso
The word dorso is a more formal, anatomical, or technical term for the back. It is frequently used to describe the upper back of animals, the back side of certain body parts like hands, the spine of a book, and the swimming style known as the backstroke.
Il cavaliere accarezzò il dorso del cavallo prima della gara.
(The rider stroked the horse's back before the race.)
Il paziente ha una piccola irritazione sul dorso della mano destra.
(The patient has a small irritation on the back of his right hand.)
Il titolo del romanzo è stampato a lettere d'oro sul dorso del libro.
(The title of the novel is printed in gold letters on the spine of the book.)
Oggi in piscina mi sono allenato a dorso per migliorare la respirazione.
(Today at the pool I practiced the backstroke to improve my breathing.)
Il mulo portava un carico molto pesante sul dorso lungo il sentiero.
(The mule carried a very heavy load on its back along the trail.)
In biologia abbiamo studiato le caratteristiche del dorso dei rettili.
(In biology we studied the characteristics of the back of reptiles.)
Summary
In short, use schiena for everyday, colloquial references to the human back, including physical ailments and posture. Opt for dorso when talking about the anatomy of animals, the back of specific objects like hands or books, or formal sporting terms like the backstroke in swimming.