How to do abdominal crunches correctly

The abdominal crunch is one of the most common exercises used to train the abdominal muscles. We like the starting position where the knees and hips are flexed to 90 degrees. This isolates the abdominal muscles and takes away the influence of the muscles that flex the hip. A common technique error is to start with the hands clasped behind the head and then to snap the head into the upright position. This puts the neck at risk of injury and really doesn't isolate the abdominal muscles. A proper technique in which the arms are folded on the chest wall, and the trunk is pulled up by the abdominal muscles themselves. This isolates the abdominal muscles and keeps the neck safe.