Upping Work Capacity

I’m gonna start implementing some crossfit and maybe some hill sprints into my training but I’m wondering what some of you out there personally do to increase your work capacity. I mean like upping my anaerobic threshold and the like.

Recently I’ve been liking rucks. 50lb or more pack for a long walk.

Tabata twice weekly, goblet squats. My morning heart rate is now down to 33.