Enduring Capacity of the Erectores Spinae Muscles in Static Work

Abstract

The enduring capacity of the erectores spinae muscles for sustained back extension was investigated in 8 normal males at the tensions of 70, 50, 40 and 30% of the maximum strength with a specially deviced dynamometer. Relatively prolonged endurance time was obtained at lower tensions; the critical tension endurable for 10-20 minutes was supposed to be 20-30% max., though muscular pain appeared already before the half of endurance. Heart rate increase was moderate. Conflicting trends were demonstrated between the mean amplitude and the slowing of EMG of the erectores spinae. The work load suffered by the latter in upright standing was assessed electromyographically as less than 2-3% of the maximum activity, and at most 20% in the case of forward bending at 45-60 degrees.