There's almost no way getting around it — if you're serving in the US military, maintaining one's physical fitness is a duty that you have to fulfill, unless you'd prefer to struggle to catch your breath.
In order to accommodate both the fluctuation of the average person's physical traits and the demands of modern warfare, the US Army's Training and Doctrine Command (TRADOC) is constantly honing its physical fitness standards. Taking a look at this evolution of physical standards with Whitfield B. East's, "A Historical Review and Analysis of Army Physical Readiness Training and Assessment" provides not only the insight to the demands of what was needed on the battlefield back then, but also answers the highly debated question of whether servicemembers back in the day could be considered fitter.
Starting in the early 1800s, United States Military Academy (USMA) cadets neglected physical exercise and merely practiced military drills — even recreational activities were frowned upon. After realizing their mistakes, Congress and Army leaders sent officials to Europe to determine the best course for implementing a physical education program for their future officers.
Tasks within this new program included scaling a 15-foot wall without using tools, vaulting on a horse 15-hands high, leaping a ditch 10-feet wide, an 8-minute mile run, and a 3-mile march carrying a 20-pound knapsack in one hour. Also recommended in this new program was the ability to dive and remain underwater for 45-seconds.
Shortly after the Civil War, the USMA appointed its first pedagogically-trained instructor, Herman Koehler, as its "Master of the Sword." As the new head of West Point's Department of Physical Education, Koehler focused on gymnastics as a key element for fitness and brought into existence the first Army-wide training manuals for physical training in 1887.
In 1906, the Army then implemented its first unit-wide physical training program. Tasks included a weekly 12-mile march for the infantry and 18-miles for horse-mounted artillery and cavalry units. Even the President at the time, Theodore Roosevelt, was obsessed about starting a physical regimen for the military — as a sickly kid during his childhood, he developed a philosophy of strenuous exercise.
World War I then brought new fitness requirements for the Army — the first manual to identify quantifiable physical objectives was developed. This Individual Efficiency Test measured combat physical readiness with the following requirements: running 100 yards in 14 seconds, a 12-foot broad running jump, an unassisted 8-foot wall climb, throwing a hand grenade for 30 yards into a 10' diameter circle, and an obstacle course run.
Shortly before the attack on Pearl Harbor and the US' involvement in World War II, the US was seen as a complacent country that neglected physical activity due to the 20 years of peace and continued innovations to make life easier — over a third of the military's inductees were considered to be in "miserable shape", and half of them weren't even able to swim well.
This proved to be a harrowing precursor to the landing of D-Day, when it was determined that a significant number of deaths were attributed to the fact that many servicemembers had drowned in waters that were 10-15 feet deep.
To address these inadequacies, in 1944, the Physical Efficiency Test Battery was created. This battery of tests included pull-ups, 20 seconds of burpees, squat jumps, push-ups, a 100-yard pig-a-back run, sit-ups, and a 300-yard shuttle run. Normative scales were included during this examination to provide participants with the added incentive to score higher and to incite a "competitive spirit" amongst themselves.
Finally, in the 1980s, testing requirements shaped into what it currently resembles within the Army. The gender-integrated Army Physical Readiness Test (APRT) evaluated soldiers on their ability to do push-ups, sit-ups, and a 2-mile run in that order, with 10-20 minutes of rest time between each event.
After receiving initial data on the results, research teams concluded that about 5% of soldiers should be able to score the maximum points allotted for the test. During the beginning of this era, there were no scoring standards for soldiers over the age of 40, and those that were only authorized to be tested on the 2-mile run.
Since then, there has been much debate with the current scoring system in the Army's physical fitness test — many scorn the "corporate fitness" model and it's detraction from its more combat-oriented roots. It remains to be seen if the Army implements a more functional assessment to meet the demands of today, such as the Marine Corps' Combat Fitness Test.
Whichever way the Army decides to keep rolling along, you can be sure that servicemembers will be profusely sweating.