Ageing modifies the fibre angle and biomechanical function of the lumbar extensor muscles.

Background: Ageing is associated with geometrical changes in muscle fascicles that may lead to deteriorations in physical functions. The purpose of this study was to study the effects of ageing on fibre orientation and strength of the lumbar extensor muscles.

Methods: Fifty two healthy, 26 younger (10 males and 16 females, aged from 20 to 35) and 26 older (10 males and 16 females, aged from 65 to 90) volunteers participated in this study. Ultrasound images of the lumbar extensor muscles were obtained with the participants in relaxed standing and half flexion (50% of the range of trunk flexion). The fibre angles at the mid-substance of the muscle were recorded. Lumbar extensor muscle strength was measured in the upright posture with a load cell.

Findings: The mean lumbar extensor fibre angles were found to significantly decrease in the half flexion posture when compared to upright stance (P<0.01). Both the fibre angle and the moment generation capability of the muscles decreased with ageing (P<0.01). There was a moderate correlation between the fibre angles in the upright posture and the muscle strength measured in this posture (r=0.40, P<0.01).

Interpretation: Age-related changes in muscle geometry and posture may partly account for the deterioration in muscle function in the elderly.