Table 2.

Lumbar muscularity (CSA of muscle-disc ratio*100) of the paraspinal muscles of the three groups using MRI

		Young group	Middle-aged group	Elderly group	p-value
PS CSA	L2-3	45.58 ± 12.18†	42.50 ± 13.81‡	31.86 ± 15.22†,‡	.004
	L3-4	64.58 ± 15.87†	57.56 ± 17.41‡	44.71 ± 15.71†,‡	.001
	L4-5	81.00 ± 17.41†	73.92 ± 20.09‡	57.31 ± 18.37†,‡	< .001
	L5-S1	90.43 ± 23.37†	81.03 ± 18.72‡	61.55 ± 18.44†,‡	< .001
QL CSA	L2-3	24.13 ± 8.19†,‡	18.39 ± 6.50†	15.91 ± 7.28‡	< .001
	L3-4	32.89 ± 11.28†,‡	24.59 ± 8.02†	19.92 ± 6.74‡	< .001
	L4-5	32.52 ± 8.33	27.79 ± 8.24	20.59 ± 7.87	< .001*
	L5-S1	Not checkable	Not checkable	Not checkable	/
GCSA of MF	L2-3	32.79 ± 8.17†	30.57 ± 8.98‡	23.86 ± 6.75†,‡	.002
	L3-4	41.25 ± 6.70†	38.47 ± 6.54‡	33.20 ± 6.11†,‡	< .001
	L4-5	58.73 ± 9.84†	56.66 ± 9.62‡	48.43 ± 7.50†,‡	.001
	L5-S1	79.33 ± 11.85†	77.62 ± 14.99‡	63.69 ± 11.15†,‡	< .001
FCSA of MF	L2-3	25.04 ± 6.57	21.44 ± 6.44	14.97 ± 4.52	< .001*
	L3-4	33.07 ± 5.96	27.56 ± 5.51	21.49 ± 4.83	< .001*
	L4-5	45.34 ± 8.43	39.53 ± 7.41	29.96 ± 6.49	< .001*
	L5-S1	57.06 ± 8.85	50.75 ± 10.69	36.10 ± 8.83	< .001*
GCSA of ES	L2-3	133.09 ± 31.26†	125.44 ± 19.56	114.58 ± 22.21†	.044
	L3-4	121.53 ± 29.70†	110.49 ± 19.95	100.31 ± 19.95†	.012
	L4-5	102.50 ± 22.33	98.36 ± 18.47	90.91 ± 18.71	.159
	L5-S1	82.88 ± 33.13†	76.13 ± 27.15	60.94 ± 21.28†	.039
FCSA of ES	L2-3	119.14 ± 32.03†	106.81 ± 18.59‡	88.66 ± 19.84†,‡	.002
	L3-4	101.99 ± 26.83†	88.11 ± 18.76‡	73.71 ± 16.99†,‡	.001
	L4-5	82.21 ± 21.01†	71.06 ± 15.95‡	57.47 ± 13.37†,‡	< .001
	L5-S1	57.52 ± 28.36†	43.12 ± 18.07‡	30.34 ± 12.84†,‡	.001

PS Psoas, QL Quadratus lumborum, MF Multifidus, ES Erector spinae, CSA Cross-sectional area, GCSA Gross cross-sectional area, FCSA Functional cross-sectional area

“†” and “‡” represents the two groups that had a significant difference, and “*” represents the three groups that had a significant difference with each other (all adjusted P < .05)