Another study found that at one training center in 2002, 3 recruits suffered stress fractures of the pubic bone, but last year the number rose to 39. The reason, General Hertling said: not enough weight-bearing exercise and a diet heavy on sugared sodas and energy drinks but light in calcium and iron.

The new fitness regime tries to deal with all these problems by incorporating more stretching, more exercises for the abdomen and lower back, instead of the traditional situps, and more agility and balance training. It increases in difficulty more gradually. And it sets up a multiweek course of linked exercises, rather than offering discrete drills.

There are fewer situps, different kinds of push-ups and fewer long runs, which Army officials say are good for building strength and endurance but often lead to injuries. They also do not necessarily prepare soldiers for carrying heavy packs or sprinting short distances.

“We haven’t eliminated running,” General Hertling said. “But it’s trying to get away from that being the only thing we do.” (The new system does include plenty of sprinting.)

Some of the new routines would look familiar to a devotee of pilates, yoga or even the latest home workout regimens on DVD, with a variety of side twists, back bridges and rowinglike exercises. “It’s more whole body,” said First Lt. Tameeka Hayes, a platoon leader for a class of new privates at Fort Jackson. “No one who has done this routine says we’ve made it easier.”

The program was largely the brainchild of two former gym teachers who now run the Army Physical Fitness School based here. They are a military version of Click and Clack, finishing each other’s sentences and wisecracking with the alternating beat of gas-fired pistons.