What is neck extension (isometric)?

Neck extension (isometric)

1. Sit in a chair, or stand up straight. If you're standing, keep your feet about hip-width apart.
2. Keep your neck straight, and look straight ahead.
3. Lace your fingers together or put one hand over the other, and place your hands at the back of your head.
4. Press your hands against your head at the same time you press your head straight back against your hands. Press firmly, but not as hard as you can. Do not tip your head back.
5. Hold for about 6 seconds.
6. Repeat 8 to 12 times.