The prone is bridge is a great exercise which develops stunning core strength. There are three different levels to this exercise and the version illustrated in the photo is the most advanced. I suggest working up to that exercise using the method outlined below.
Muscles involved: Rectus Abdominis, External Obliques, Hip Flexors
Action: Lie face down on the ground or floor and stretch out in a prone position. Then lift your body up so that you’re balanced only on your forearms and toes. Now tuck your pelvis. This basically means rotating the lower part of your pelvis toward the ground, also referred to as posterior pelvic tilt. This tilt should cause you to go into a neutral spine, where there’s almost no extension in the lumbar spine. Then hold this position for 30 seconds and rest.
To increase the difficulty of this exercise, get into the position where you’re balanced on your forearms and toes with pelvis tucked. Then raise one leg and hold for 30 seconds. Repeat on the other side for 30 seconds and then rest.
To advance this exercise one step further, once again, get into the position where you’re balanced on your forearms and toes with pelvis tucked. Then raise opposite arm and leg, simultaneously, (as illustrated in the photo) and hold for 30 seconds. Repeat on the other side for 30 seconds and then rest.
Comments: This exercise not only develops strength in the muscles involved, it also teaches you to maintain stability (relative stillness) in the lumbar spine while performing exercises in the prone position, such as push ups and prone rows, and during movements which require you to stabilize your spine while your arms and legs are moving.