Lumbar myoelectric spectral analysis for endurance assessment. A comparison of normals with deconditioned patients.

A myoelectric protocol to objectively discriminate between test subjects based on trunk muscular performance differences (endurance) was investigated in a group of 11 healthy volunteers and ten industrial patients undergoing functional restoration for chronic disabling spinal disorders. The subjects performed a standardized exercise protocol, holding their upper torso unsupported for successive fixed-time trials while electromyographic (EMG) signals were recorded from erector spinae. A Fast Fourier Transform allowed calculation of the initial mean power frequency (MPF) for each trial. Isokinetic extensor trunk strength was independently measured at each session for comparison with myoelectric signal analysis. The investigation revealed significant differences in group statistics between patients in early rehabilitation and their subsequent tests, as well as between their initial test and the normal subject scores. However, test sensitivity for identifying patients with "low endurance" is questionable. There was no significant correlation between EMG initial MPF measures and isokinetic extensor trunk strength measures, even though all patients showed isokinetic improvement. Data suggest that the protocol used and myoelectric power spectrum temporal shifts may have some value for identification of individual subjects with endurance limitations (or fatigue resistance) in patients of this type. However, lack of a "gold standard" for comparison presents difficulties in documenting the value and validity with respect to endurance. The test may be of value to measure relative loads.