Figure 2. The first 30 s of motor unit activity.

A, all contractions (n = 13) from one subject in which the start of unit firing could be followed in different units (each contraction a different colour in the online version). Three different units, from this subject, in which the start of firing could be followed during several contractions (B, unit 1 during 2 contractions, each contraction shown in a different colour in the online version; C, unit 2 during 3 contractions; and D, unit 3 during 4 contractions). Note the similar time–frequency plots for a given unit.