体幹前屈動作中の腰椎に対する機械的負荷と体幹筋活動の関係

Relationship between the Mechanical Load on the Lumbar Spine and Trunk Muscle Activity during Forward Bending of the Trunk

　健常者の体幹前屈動作中の椎間板内圧，姿勢変化，および体幹筋活動を同時に測定し，荷重負荷の影響を理論値と比較し検討した．その結果，機械的負荷は体幹傾斜角度に比例して増加し，同時に背筋の筋活動も活発化したが，腹筋はほとんど活動しなかった．一方，荷重による負荷の増大量は，いずれの傾斜角度においても実測値が理論値を上回っていた．この差には主に背筋による負荷の増大が関与していると推定された．すなわち，前屈動作による腰椎への負荷の増大には，体幹傾斜に伴う物理学的増大と，背筋の活動による生体力学的増大がある．

　Little is known about the relationship between intradisc pressure (IDP) and trunk muscle activity during forward bending. We clarified the relationship between the actual and theoretical load on the lumbar spine with and without the application of external weights. We measured IDP, EMG of the trunk muscles, and trunk motion analysis in 3 young healthy men simultaneously with and without lifting a weight of 10kg. Recorded values were compared to theoretical values based on the lever principle. Load on the lumbar spine and EMG of the back muscles increased in proportion to the tilt angle with and without external weights. External weights induced no significant activity in the abdominal muscles. Actual measurement exceeded theoretical values at all trunk tilt angles. We found that the increase in actual spinal load during trunk flexion in healthy individuals consisted of the theoretical spinal load and the load generated by back muscle activity.