Age affects the latency of the erector spinae response to sudden loading.

Background: Aging and a past history of low back pain are risk factors for a future low back pain. Recent findings have demonstrated an impaired feed-forward control of paraspinal muscles during upper limb loading in low back pain patients as well as decreased feed-forward mechanism in elderly. The aims of the current study were to assess the age-related changes in paraspinal reflex latencies, flexion movement as well as flexion moment of the lumbar spine during sudden upper limb loading and the expectation effects via feed-forward mechanism on these postural responses.

Methods: The paraspinal reflex latencies for upper limb loading during unexpected and expected conditions were measured in erector spinae and multifidus muscles by surface electromyography from 23 young healthy subjects (aged 30 or younger) and 15 healthy elderly subjects (aged 60 or older). The kinematic and kinetic data were obtained simultaneously from a magnetic motion measurement system and a force plate, which were used to calculate flexion moments.

Findings: The age was found to have a significant effect for delaying the paraspinal reflex latencies. Expectation shortened the reflex latencies, as well as decreasing the flexion movement and the flexion moment of the lumbar spine. The expectation effects on theses postural responses were reduced by subject's age.

Interpretation: These findings suggest that aging process is associated with a decreased motor control of the spine, particularly via reduced feed-forward control of paraspinal muscles. These findings may contribute to decreased ability to stabilize the spine and development of low back injury in elderly.