Learn French: L'athlète est en train de transpirer autant que le joueur. - The athlete is sweating as much as the player.

You use aussi ... que when you are comparing adjectives or adverbs (like saying someone is as fast as someone else). But when you are comparing verbs, like the action of sweating (transpirer), you must use autant que. It translates directly to 'as much as'.

If this sentence used the passé composé, where would autant go?

In compound tenses like the passé composé, autant is usually placed between the auxiliary verb and the past participle, while que stays with the second part of the comparison. For example: L'athlète a autant transpiré que le joueur. In our current sentence, because we have an infinitive (transpirer), autant que simply follows it.

Could we just say L'athlète transpire autant que le joueur?

Yes, absolutely. French uses the simple present to express both 'sweats' and 'is sweating'. However, the phrase être en train de followed by an infinitive is used to strongly emphasize that an action is currently in progress, like saying 'is in the middle of sweating'.

How do we know if l'athlète is male or female in this sentence?