Full range neck flexion is somewhere between 82 and 90 degrees for males. Females in general have less range of motion in flexion then their counterpart. When training full range flexion start the exercise in a neutral position with the head slightly retracted. Beginning the exercise from neutral in retraction elicits about 10% more neural activity hence recruiting the most neck muscular. You need a great 'start' to Get Strong.

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Screenshot 2015 11 06 20 45 14 1