Researchers Put the Twist on Back Muscles
Muscles seem to have minds of their own. They contract in different ways and at different times depending on body position and activity. Researchers want to learn more about how muscles work during twisting or turning movements. This information may be helpful in preventing back injuries caused by repeated twisting motions.

Researchers studied eight muscles of the back, trunk, stomach, and hip. They found that some muscles only contract when the body twists to one side. Sometimes the activated muscle is the one on the side of the twist. Other moves cause the muscle on the opposite side to work. Some of these muscles contract with movement in both directions. Muscles also respond differently in sitting versus standing positions.

A muscle that runs along the back of the spine called the erector spinae contracts in two separate parts. One part is active when the trunk twists to the right. The other part contracts when the trunk twists to the left.

Muscles are known to work at different times depending on the activity. Muscles on both sides of the body work to balance each other. This gives the body stability. The same muscles may act differently when the body is sitting versus standing. Knowing how and when muscles work may help prevent injuries.
References
Eva A. Andersson, MD, PhD, et al. Diverging Intramuscular Activity Patterns in Back and Abdominal Muscles During Trunk Rotation. In Spine. March 15, 2002. Vol. 27. No. 6. Pp. E152-160.