Sit-Ups, Crunches, Planks, Knee-Ups: The Evolution of Core Fitness Testing

Core strength testing has come a long way from the straight-legged, twisting sit-ups used before World War II.

Curl-ups - Physiopedia

How to Do A Plank the Right Way, Abs and Core Exercises

Why You Can Stop Doing Sit-Ups - WSJ

The Truth about Whether You Should Crunch or Plank Your Way to a

The Major Differences Between Sit-Ups and Crunches

Sit-Ups, Crunches, Planks, Knee-Ups: The Evolution of Core Fitness

5 Oblique Exercises for Stronger Core and Spine Support

Can I build muscle just by doing push-ups and deadlifts? - Quora

Can you do sit-ups while pregnant?

Sit-ups: Techniques, benefits and variations on the classic