Natural aging course of lumbar extensor muscle mass and strength in community-dwelling older women: a 1-year prospective observational study

Background Although the loss of skeletal limb muscle mass and muscle strength in the elderly have been demonstrated, the aging process of the back muscles to maintain core stability is not well known. This 1-year prospective observational study aimed to investigate the natural aging course of the lumbar extensor muscles (LEMs) compared with the extremity muscles and determine whether muscle strength or mass decreases more in community-dwelling older women. Methods Twenty-four older urban-dwelling women aged 70 years or older were initially enrolled. Their demographic variables, conventional and spinal sarcopenia indices, and functional outcome parameters were evaluated. We also measured back extensor strength, radiological parameters for spinal sagittal balance on whole-spine radiography, and volumetric parameters of the LEM on computed tomography. Results After the exclusion of 6 subjects, 18 older women were finally analyzed. All variables related to extremity muscle mass, muscle strength, physical performance, and LEM volume declined over the study period, but the changes were insignificant. However, back extensor strength decreased significantly (median, first, and third quartile: 35.20 [30.80, 44.00] N to 31.40 [29.25, 37.90] N, P = 0.026). Among spinal sagittal balance-related parameters, lumbar lordosis (44.25 [39.30, 47.35]degrees to 43.15 [31.43, 45.75]degrees, P = 0.043) and sagittal vertical axis (33.85 [3.57, 58.75] mm to 45.15 [25.35, 58.68] mm, P = 0.004) showed significant changes during the study. Conclusions When the natural aging course of LEM in women aged 70 years or older was observed for 1 year, muscle mass decreased less than back extensor strength and spinal sagittal balance. Measurements of back extensor strength and spinal sagittal balance are necessary for the clinical evaluation of spinal aging.