Change of a principal investigator

To investigate change of shoulder muscles by measuring muscle activity according to the position of the backpack.

Most of modern people, including students and office workers, wear backpacks for a considerable amount of time. There have been prior studies on the change in muscle activity around the spine and shoulders muscles according to the weight of the backpack, but studies on the change in muscle activity according to the direction of the bag are insufficient. So this study is to evaluate the effect on the musculoskeletal system by comparing the activity of the muscles around the shoulder according to the anterior or posterior wearing of the backpack.

Muscles around the shoulder are composed of: Serratus anterior, trapezius(upper and lower) which control scapular movement and deltoid muscles which activate shoulder abduction directly. We would like to focus change of these muscles's activities when carrying a backpack according to the anterior or posterior direction and bilateral or unilateral.

To measure muscle activity, eight-channel electromyography (EMG) Using Nicolet EDX (Natus Medical Inc., San Carolos, CA, USA), surface EMG (sEMG) signal were used.

Inclusion Criteria:

• Healthy adults from 20s to 50s

Exclusion Criteria:

• Restriction of joint motion range of shoulder and elbow
• Hisory of upper limb surgery in the past 6 months
• If there is an external wire such as a temporary external pacemaker or central line guide wire