This study was performed to figure out mechanical load on the lower back during lifting objects by measuring the mean amplitudes and durations of compound muscle action potentials of the lumbar extensor muscles in eight postures from 30 healthy male adults.

As follows:

1) The highest value of mean amplitude of lumbar extensor muscle activities was 485.0±250.7 uV which was in the posture of extending both upper extremities forwardly and upright position.

2) The lowest value of mean amplitude of lumbar extensor muscle activities was 107.1±54.6 uV in the posture of both wrist joints to anterior axillary fold and partially flexing and leaning of both knees to fixed wall.

3) There was no significant differences of mean duration of compound muscle action potentials of lumbar extensors in 8 postures.

In conclusion, to reduce mechanical load on the lumbar spine during lifting objects was lowest with the posture that the object is close to trunk lowering the body posture with flexing knee joints and leaning to fixed wall.