Back function testing and paraspinal muscle magnetic resonance image parameters: their associations and determinants : a study on male, monozygotic twins

Abstract

Factors associated with three commonly-used back function tests and muscle morphology based on magnetic resonance images of the back muscles were investigated in 65 pairs of monozygotic male twins, aged 35 to 67. The isokinetic lifting test results had low correlations with psychophysical lifting (p = 0.30) and static back endurance (p = 0.30), and the latter two were unrelated. The cross-sectional areas of the erector spinae, quadratus lumborum, and psoas major muscles were moderately correlated with isokinetic lifting strength (p = 0.46 to 0.53), but did not correlate well with psychophysical lifting and static back muscle endurance. The signal intensities of the muscles had poor correlations with the back function tests (p ≤ 0.20). None of the imaging measures or the back function tests was useful as a predictor of future low back pain over 12 months of follow-up, in the 43 men who reported no low back pain in the year preceding testing. A combination of genetics and shared childhood environment played a dominant role in determining back muscle cross-sectional area and the functional capabilities of the back, explaining as much as 73% of the variance; physical loading, back pain history, overall health, and anthropometric data had a comparatively minor role. The major role of familial aggregation suggests that in healthy adults, the potential of interventions to increase and sustain back function, as evaluated by the three tests or by muscle morphology based on magnetic resonance images may be limited, without marked long-term lifestyle changes.