Task-related variations in motoneuronal drive to a human intrinsic hand muscle

Maximal electromyogram (EMG) levels of the first dorsal interosseus muscle (FDI) were studied during maximal pinching between index finger and thumb at two different wrist angles. Despite the fact that there was no change in the biomechanical conditions for the FDI, the maximal EMG levels of the FDI differed significantly; typically EMG levels were higher while pinching at a maximally flexed wrist angle compared to a maximally extended wrist angle. The stability of the EMG recordings was checked with supramaximal peripheral nerve stimulation. Significant changes in the area of the compound muscle actions potentials (M-waves) were obtained. However, these changes could not explain the observed differences in the maximal EMG levels. Our results suggest that the ease of producing a maximal drive to the FDI muscle depends on the motor task.