I have a band around my feet. This exercise develops lumbo-pelvic stability, and the band really adds to the challenge.
Before each rep, take a 360 degree breath in, do a 360 degree brace, tuck your ribs towards your hips, and squeeze your glutes. This will keep your pelvis and hips stable.
Now simultaneously extend your opposite arm and opposite leg.
Make sure you extend your leg directly back, and not to the side. Lift your arm so it’s parallel to the ground. Don’t lift too high.
Contract your arm, and make a fist. You should even be contracting your lats. The goal is full body tension, but particularly in the lumbo-pelvic region.
Reach back with your leg by extending your hip, not by bending and extending your knee.
Point your foot towards you (dorsiflex).
If you are performing this exercise correctly, aside from the arm and leg that are moving, the rest of your body should remain in a fixed position.
For the duration of the exercise, your body should remain square to the floor (nothing should rotate), and your head, torso, hips, and foot should be in a stacked position.
Do not allow your lower back to hyperextend or ribcage to flare.
The goal here is generating tension, and maintaining proper body positioning.
Most people just mindlessly go through the motions and do not generate enough tension, nor do they maintain proper body positioning.
If you are performing this exercise correctly, including the basic variation, it should feel tough.