ABOARD THE USS BOXER—About two dozen Marines and sailors gathered in the gym recently for some friendly competition. They were there for the 1,000-Pound Club, to see who could squat, bench and deadlift the most weight on this warship.

That day’s round went to the Marines. Sgt. Emmanuel Addomensah, 22 years old, scored 1,490 pounds across all three categories, just 55 pounds short of the ship’s record. That one was set by a 31-year old naval officer, Lt. Brandon Schabacker, who is embedded as a doctor in the Marines.

“I’m...