The fibre type composition of thoracic and lumbar paravertebral muscles in man.

Samples of longissimus and multifidi muscles at the thoracic and lumbar levels of the spine were examined histochemically on autopsy specimens from 21 adult male subjects (aged 22 to 46 years) and on biopsies from 17 adult patients during surgery for disorders of the lumbar intervertebral disc. In the superficial and deep thoracic muscles, 74% of fibres were of the Type I variety. In the lumbar region, Type I fibres amounted to 57% in the superficial, and to 63% in the deep muscles. The diameter of Type I fibres was significantly greater than that of Type II fibres.