Athletic shorts--what to wear under them?

I was recently gifted a couple pairs of of athletic shorts. Unlike the athletic shorts I buy for myself, they did not come with a liner (?)–basically built-in underwear–they’re just short. What does one wear under such shorts? Regular cotton underwear? Do I have to buy a separate athletic liner, eg sports underwear? Or am I supposed to just go commando?

ETA, I guess this might qualify as Game Room or IMHO, but we’ll see what the all-knowing mods think.

Assuming you’re male, you want support for anything vigorous and onlookers would probably not want a burlesque show.

Look for specific sports underwear as cotton gets abrasive when wet.

Jockstrap.

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Synthetic compression briefs. I agree with running coach that anything cotton is a no-no.

Boxer briefs.

Thanks for the replies. I’m a little annoyed that I have to spend money to make my gifts work effectively, but here we are.

Yeah, this is what I do, depending. Not the old fashioned gym jock
Look for a running jock in particular.

I go with a more compression type boxer brief when it’s not hot.

I also ran in Ex Officio briefs for quite a while until they died after a couple years.

If they were padded cycling shorts, nothing.

Synthetic compression boxer briefs are what my son’s sports teams wear for running (cross country and track)