Exercising with your pack on now makes hiking with it later feel like less of a workout.
On endurance days, you want to approximate the distance and loads that you’ll be carrying on your big trek. Use the same gear you would on the trip: boots, pack, trekking poles. Stuff your pack with 2-liter soda bottles filled with water; in addition to working your legs, you’ll prime your torso and shoulder muscles. As you hike, tap that water to stay hydrated, but don’t pour it out at the top of the climb.