Vastus medialis muscle: instantaneous signal. Slight extension of the leg.

Vastus medialis muscle: instantaneous signal.

Map of the differential voltage distribution on the surface of the vastus medialis muscle. Grid of 5x13 electrodes with diameter of 3 mm spaced by 8 mm (56 x 112 mm).

Acquisition rate: 2048 frames per second.

Reproduction rate: 20 frames per second (100 times slower) with image interpolation.

The motor unit action potentials, each comprising a positive peak (red) and a negative peak (blue), are generated in the center of the image (innervation zone) and propagate toward the knee (upper right) and the and hip (lower left) along the muscle fibers which are at a 45o angle with respect to the femur.