stress harder

In a book I was reading yesterday about soldiers being like normal people, except that they drink and smoke more: they stress harder. It was the first time I'd seen the word stress as a verb used in such a connotation. The closest meaning I can find for the verb is to subject to stress or strain, so it's a verb that would require a doer and a doee, which is not the case here. It's English verbing its nouns again.