Align With Your Midline
Although the side-neck muscles have to work in Trikonasana, you can reduce the strain if you keep your neck in line with the rest of the spine and don't try to look up at the ceiling right away. With your head in this position, you can use a couple of simple techniques to check your alignment—first in the left-right orientation, and then in the front-back plane.
Set up to do Trikonasana to the right, so that you can see your head and torso in a mirror. Once you're in the pose, look straight ahead and draw an imaginary line from your navel up through your breastbone. Even better, use a spotter with a good eye or a helper with a long dowel or broomstick to help you see the line. Ideally, the line should continue from the center of your torso to your nose, through the center of your face. If your head hangs below the line, your neck will be sidebending to the right. If your head is lifted above it, your neck will be sidebending to the left. Either way can strain your neck. After correcting your position by centering your head on the line, imagine that you're lengthening your spine away from the pelvis, all the way up through the crown of your head, which should help decompress your neck. The left and right sides of your neck should be just about even in length.
The second dimension of aligning the neck with the rest of the spine involves the front-back orientation. Many people tend to keep their heads forward in their everyday posture, so "forward head" is a common problem in Trikonasana. This misalignment is easy to correct by doing the pose with your back to a wall. For Trikonasana to the right, set up with your right buttock lightly touching the wall, and your right foot and left heel near it. Come over into the pose. Ideally, your torso and head should be in the same plane as your legs, and that plane will be parallel to the wall. With your right buttock touching the wall, your shoulders, head, and left hand should be within a few inches of it. If your head is several inches away, correct the position by bringing the back of your head closer, though not necessarily touching the wall. Make sure you haven't overarched your lower back; check that your back ribs and shoulders are also near the wall.
Now that your head and neck are aligned with the rest of your spine, let's make sure the curve of your neck is optimal before you turn your head. You can learn to feel the proper curve while you're upright, and then find it again while sideways in the pose. Sitting or standing, place the palm side of three fingers across the back of your neck, just below the base of your skull. Drop your chin toward your chest, and you should feel the back of the neck flatten and the nuchal ligament (a large, very firm ligament that's right in the center of the back of the neck) rise up under your fingers. If you lift the chin back up and keep going until you're looking at the ceiling, your neck will be hyperextending and you'll feel the base of your skull compressing into your neck. The position you want, both for Trikonasana and everyday activities, is a soft curve forward, neither flat nor hyperextended. In the upright position, your chin and gaze should be level. (You may have to confirm that in a mirror.)!--page-->