Learn French: Il s'épuise moins que moi grâce à sa résistance. - He tires himself out less than me thanks to his stamina.

Here, we are comparing the intensity of an action. To compare verbs, the comparative word (moins, plus, or autant) goes directly after the conjugated verb, followed by que. So, s'épuise moins que means 'tires himself out less than'.

Why do we use moi instead of je after que?

In French comparisons, the pronoun that comes after que must be a stressed pronoun (like moi, toi, lui, elle), not a subject pronoun. Even though in formal English you might say 'less than I', French always requires the stressed form here.

Could I use à cause de instead of grâce à here?

No, because grâce à is specifically used for a positive cause (thanks to). Since his stamina is a helpful trait, grâce à is correct. If the cause were negative or a hindrance, you would use à cause de (because of).

What would happen if I dropped the s' and just wrote Il épuise moins que moi?