How do Navy SEALS get so strong?

Answer 1

Huge ammounts of PT. During BUDS as an example, the average distance that a trainee runs each and every day is 12 to 15 miles. Pushups etc. zillions. Long distance swims, up to 10 miles. Standing on your head or other tortures, constant.

Answer 2

BUD/S consists of a three-week 'Indoctrination Course', known as INDOC, followed by three phases, covering physical conditioning (seven weeks), diving (eight weeks), and land warfare (ten weeks) respectively.

In the first phase, BUD/S students are divided into 'Boat Crews' which can consist of six to eight men. Although some exercises will be undertaken as boat crews (such as 'log PT', which requires boats crews to exercise with logs that weigh 150 lb (68 kg) each, and 'Surf Passage', where boat crews must navigate the Pacific surf in inflatable boats), the first phase of BUD/S also consists of a series of demanding individual physical tests.

The first phase is most well known for "Hell Week", 132 hours of continuous physical activity, which now occurs during week three. A student may drop on request (DOR) from the course at any time. Classes typically lose around 70-80% of their trainees. There has been at least one BUD/S class where no one has completed the program.