Illustration of the synchronization principle of basic MU firing patterns of two MUs, considering MU1 as a reference one (blue, bottom) and applying the synchronization of pulses to MU2 (green, NS).

Three time windows were used: Δt = ± 2 ms (yellow), ± 4 ms (orange), and ± 6 ms (red). The dots highlight individual pulses of MU2, which were shifted in time (left or right, as indicated by arrows) to coincide with reference impulses of MU1 when the time interval between the pair of impulses of MU2 and MU1 was less or equal than |Δt|. The level of synchronization was proportional to Δt, illustrated in this example by increasing numbers n of shifted impulses—namely, n = 3 for Δt = ± 2 ms, n = 5 for Δt = ± 4 ms, and n = 8 for Δt = ± 6 ms.