Comparison of the thickness of Longus colli and Sternocleidomastoid according to weight of backpack and measurement of craniocervical angle

[...]theoretically, if the head moves forward from the weight center of gravity, the head and neck reflexes as vestibular neck reflex (the neck posture stabilization reaction from the cervical nerve and the labyrinth of the ears)3. [...]movement of the COG not only causes the ankles, hip joints or the head to face forward but cause musculoskeletal changes as the shortening of the extensor muscles at the back of the neck and the tightening of the neck muscles at the front. [...]the thickness of longus colli muscle tended to lessen with the increase of load that carrying the backpack for elongated time would have led to significant differences. [...]if the load of the backpack increased or if the backpack was carried for elongated time, the thickness of longus colli muscle may become thinner, causing weakness of the muscles. Based on such results and conclusions from prior researches, when backpacks are applied for longer time as the usage of general backpacks, or if heavier backpacks, the usage of such backpacks may cause pain, and even changes of the backpack may be caused. [...]it could be said that the proper weight of the backpack without the change of the craniovertebral angle is ideal at the scope of 10% or less of the weight without changes in body balance or change of muscles. [...]the remaining muscles other than longus colli muscle and sternocleidomastoid muscle were not measured that the changes of these muscles were unknown, and weights beyond 15% were not measured, causing difficulty in verifying changes arising from heavier loads, and variables of time after carrying the backpacks were excluded. [...]in future research, researches complementing these limitations to add variables on time regarding loads beyond 15% with more female subjects and more subjects are needed. 4.