Figure 1. Examples of postural after-contraction movements.

A, goniometer traces showing non-volitional arm abduction movements in the right (Test) and the left (Control) arm following a bilateral ‘control type of conditioning procedure’ consisting of four steps: active arm abduction up against the stands (step 1), forceful abductor contraction for 5-10 s against the stands (step 2; indicated also by filled bar), relaxation during 4-8 s while the experimenter held the arms against the stands (step 3), and lowering of the arms back to the initial slightly abducted position during 3-5 s; this was performed by the experimenter during continued relaxation (step 4). B, non-volitional abduction movement missing in test arm for which the conditioning forceful abductor contraction (indicated by filled bar) was performed in the initial intermediate position of the arm (i.e. where the abductor ‘hold-short’ requirement was not fulfilled). Arm abductions are indicated by upward deflections in goniometer traces. In this and in Figs 4–6 the calibration mark 0 deg indicates the natural resting position of the arm during relaxation. Low-amplitude oscillations in goniometer traces were induced by respiratory chest movements.