LAUSR

OBJECTIVE We describe a mathematical model to calculate a single muscle fiber action potential (AP). Based on a marching band pattern, it is an enhancement to our previously described "modified line source" model. METHODS Calculations were performed using an Excel spread sheet. AP was simulated for a 200 mm long muscle fiber with 60 µm diameter, propagation velocity of 4 m/s, and end-plate located at the center. Several different electrode locations were used to calculate the AP. RESULTS The AP amplitude was highest at the end-plate where the waveform was biphasic with initial negativity. When the electrode was moved towards the tendon, the amplitude decreased for the first 1.5 mm. The AP was triphasic and its waveform was relatively constant at electrode positions beyond 1.5 mm from the end-plate. It matched the calculations using the modified line source model. When the electrode was near the tendon, the AP amplitude decreased asymmetrically and waveform became biphasic resembling a positive sharp wave. DISCUSSION The model is conceptually and computationally simple. It simulated the expected AP shape at different electrode positions along the muscle fiber. The waveforms are similar to those obtained from mathematically complex volume conductor models. SIGNIFICANCE The revised model can be useful for teaching and future simulation studies.