First, the principles of the routine:

1. Do it as a circuit with 30 seconds between exercises. Shoot for four to eight repetitions of any exercise or hold any position for just a few seconds, unless otherwise noted. If that’s too easy, add resistance or drop the exercise.

2. You’re finished with an exercise when you can no longer hold a position or do another strict rep or you begin to shake.

3. Start with one time through the circuit to learn the exercises. Two circuits will be plenty as you progress because you’ll be adding resistance to the exercises.

4. Don’t let poor form take over. Poor form defeats the purpose of the workout because you’ll compensate for the weaker core muscles by using the stronger ones.

5. Don’t hold your breath during the exercises.

6. As you gain strength, drop the exercises that become easy. They are no longer your limiters, and you’ll be able to spend more time working on the harder exercises.

1. Strict Sit-Ups

T argets: Psoas (deep hip-flexor muscle). Used in cross-country skiing, running, and any form of hip flexion past about 60 degrees. Also engages the rectus abdominis (six-pack muscles). Strengthening these muscles can help alleviate the lower-back pain that often accompanies sitting.

How to: Assume a normal sit-up position—knees bent to about 70 to 90 degrees, back flat on the floor, toes hooked under something so you can pull against them. Cross your hands on your chest so your fingers are resting on your collarbones. Slowly and in control, sit up by flexing only at your hips. Do not crunch by curling your spine. Keep your spine in a neutral (straight) position while coming up to the point where your elbows touch the top of your thighs. Return to the start position for one repetition.

2 . Hitler’s Dog

Targets: Hip flexibility and transverse abdominis—the deepest ab muscles that live underneath the six-pack muscles; these are recruited in just about every limb movement. This move is also great for calming a cranky lower back.

How to: Get on all fours with knees directly below your hips and hands directly below your shoulders. Pick up one leg; while holding the knee bent at 90 degrees, draw a big ellipse in the air with your knee. The action sort of mimics the action of a dog peeing on a fire hydrant. While you’re doing that, point the arm opposite the moving leg directly in front of you, like Superman. You may not feel this exercise is tiring, but that’s probably because you have poor hip mobility. Try for 10 slow and strict rotations of each hip.

3. Windshield Wipers

T argets: External and internal abdominal obliques used in all rotational movements, like swinging a bat or golf club.

How to: The name for this move describes the action of your legs as they wipe across an imaginary windshield. Lie on your back with your arms outstretched to your sides and palms placed against the floor. Now, flex your hips so that your feet are together and pointed at the ceiling. Slowly rotate your hips to lower your feet to one side, keeping the feet locked together and knees straight. You’ll want to resist the rotation of your shoulders by pushing down hard with your hand on the side you are rotating toward. Lightly touch the floor with the side of the lower foot before raising both feet back to the 12 o’clock position and onto the other side. That’s one rep. Do this slowly and controlled. If you can’t keep you knees straight or legs together, bend your knees, keeping them pointed at the ceiling when you’re in the 12 o’clock position.

4. Three Point

T argets: The full core structure, front and back, necessary to stabilize the hips and shoulders. This move teaches the brain to fire several core muscles while holding tension from hands to the feet—an especially useful skill for climbers or anyone doing quadrupedal sports.

How to: Assume a good push-up position (a straight line running the length of your back and legs) with hands directly under your shoulders and feet spread about two feet apart. Pick up one hand without rotating your shoulders or hips. Point that hand straight out to the front, in line with your spine, and hold until you feel your shoulders rotate, hips rotate, or back sags. Anything that gets out of line from where you were when you started in the push-up position indicates a failure in strength and the end of that isometric contraction. Pick up each limb in turn and hold until failure. When this is no longer a challenge, you can pick up the opposite hand and foot and hold that. Add a weight vest for an additional challenge when you can hold the posture for more than ten seconds.