For core training always use 15 to 30 higher repetitions unless otherwise noted.

Bent Leg Sit-ups

This is a good exercise for abdominal strength and endurance. On your back with arms crossed on the chest and knees bent, curl up to a semisitting position, and return. Repeat 10 to 15 times. Variations: Do repetitions very fast. Exercise on an inclined board. Hold a weight on your chest.

Basket Hang

This is a more advanced exercise. Hang from the bar with an underhand grasp. Raise your legs into a "basket" and return. Do as many as possible.

Planks

In prone position, resting on your toes and elbow, with your torso and legs maintaining a straight line (plank), hold your position for increasing lengths of time, starting with whatever is comfortable and repeating two or three times. The goal is to hold your position for 1½ minutes. Repeat twice with a short rest separating the two planks. These can also be done on your right and left sides.

Crunches

Lie on your back with your hands crossed to opposite shoulders. Balance on your buttocks with straight legs extended and head and back off the floor. Begin a series of 'crunches' by touching your elbows to your knees and then extending, while remaining balanced. Repeat as many times as possible up to two sets of 25 to 30 repetitions.

Leg Lifts

This is a good exercise for back strength and endurance. Lying facedown on the floor, with a partner holding your trunk down, raise your legs 5 to 10 times. Avoid hyperextension.

Trunk Lifts

Lying face down on the floor with fingers laced behind your head and ankles anchored to the ground, raise your trunk 5 to 10 times. Don't overextend.

Lower Back Exercises

More information on core training is available at FireFit.