This is the 6960th most frequent Spanish word.
durso
It seems "durso" is not a standard Spanish word. Could you mean "dorso," which translates to "back" or "reverse side" in English?
Here, 'durso' is used as an adjective describing the path, which is challenging or tough.
El camino hacia la cima de la montaña es muy durso.
The path to the top of the mountain is very tough.
In this sentence, 'durso' refers to the stiff or hardened feeling in the muscles due to strain.
Después de tanto ejercicio, mis músculos están durso.
After so much exercise, my muscles are stiff.
Here, 'durso' metaphorically describes life circumstances as challenging or difficult.