'Keep going!' — shouted at someone else. On your own skin the grammar points outward.

What a Japanese person actually thinks
Reads as encouragement aimed at the viewer, like a banner at a sports day. Warm, ubiquitous, and grammatically pointed away from you.

Meaning

Literally: stubborn + stretch + imperative
Actually: The imperative form: you are telling someone to persevere. It's what a crowd shouts at a marathon.

Scores

Naturalness●●●●●

One of the most-used words in the language. The issue is who it's addressed to.

Coolness●●●●●

Also so common that it carries no weight — closer to 'good luck!' than to a creed.

Watch out

mediumThere's a real cultural critique of 頑張れ in Japan: telling an exhausted or depressed person to try harder is understood to be actively harmful. The word is not uncomplicated here.

Get this instead

一生懸命 isshōkenmei
with everything I have

Describes you rather than instructing the reader. Same spirit, correct direction.
不撓不屈 futō fukutsu
indomitable

The compressed, formal version — a statement rather than a cheer.

On skin

頑張れ

Orientation: vertical

Brush.