Intradiskal pressure, intra-abdominal pressure and myoelectric back muscle activity related to posture and loading.

Intradiskal pressures, intra-abdominal pressures and myoelectric activities of posterior back muscles have been measured simultaneously in vivo in 4 subjects. Five different angles of forward flexion were studied while externally loading the trunk with 200N. At 30 degrees of forward flexion studies were made when the load was increased from 0 to 300N. Asymmetric loading was studied with the trunk erect, in lateral flexion and in rotation. The measurement parameter values all increased when the angle of flexion increased and when the external load was increased at a fixed angle of flexion. Linear relationships were established. During asymmetric loading pressure values and the myoelectric activity increased. The increase in myoelectric activity was comparatively greater on the contralateral side of the lumbar region and on the ipsilateral side of the thoracic region. The disk pressure, the intra-abdominal pressure, and the FRA-values were higher throughout when the trunk was loaded in rotation, than in lateral flexion.