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.

The 10 Best Sit-Up Alternatives for a Stronger, More Powerful Core

Here's What A Good Core Workout Really Looks Like, thePTDC

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Freeletics Exercises: Crunches

The McGill Big 3 For Core Stability – Squat University

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

The Major Differences Between Sit-Ups and Crunches

Exercise Tutorial - V-Up

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

Pavel Tsatsouline's Guide to Pushups, Sit-Ups, and Squats