The F-wave in the vastus lateralis M. and the segmental motor conduction times for L2/L4 motoneurons

The study was performed in 30 normal subjects. Electrical stimulation was applied to the femoral nerves and the muscle evoked potential (CMAP) together with their late components were recorded from the vastus lateralis muscle bilaterally (60 nerves). Features of the late component demonstrating its antidromic nature (F-wave) were proved. Additionally, in each subject transcranial cortical (C) magnetic stimulation and root (Rx) magnetic stimulation at the level of the L3-L4 was applied. The measured latencies of respective motor evoked potentials C-MEP (relaxed muscles), CA-MEP (activated), Rx-MEP as well as the latencies of peripheral CMAP and F-wave allowed the calculation of the derived parameters, i.e. segmental times of motor conduction: central, root and peripheral. The normative values were established. The F-wave measurement also allowed for the calculation of the so-called real central conduction time, which proved to be significantly shorter than the corresponding times previously established for the lower situated L4/S1 motoneurons. This finding suggests usefulness of the method in the precise diagnosis of the lumbosacral spinal enlargement.