Determinants of paraspinal muscle cross-sectional area in male monozygotic twins

Background and Purpose. The purpose of this study was to investigate the general magnitude and relative contributions of anthropometric, lifestyle, and medical history factors and familial aggregation (combined effects of genes and early environment) as determinants of paraspinal muscle cross-sectional area (CSA). Subjects. The subjects were 65 pairs of male monozygotic twins aged 35 to 65 years ((X) over bar=49, SD=8). Methods. Study methods included magnetic resonance imaging, percentage body fat determination, and a detailed interview. Results. Most of the anthropometric factors were associated with the CSAs. Familial aggregation was the strongest determinant, however, explaining 66% to 73% of the variance in the outcomes beyond what age alone predicted. Levels of occupational, sport, and leisure-time physical activities reported by the subjects had negligible effects. Conclusion and Discussion. The CSAs of the paraspinal muscles were influenced more by some combination of genes and early environmental factors than by anthropometric factors and lifestyle choices in adulthood.