Figure 4. Effects of voluntary background contraction on postural after-contractions.

Arm abductor postural after-contractions provoked by a ‘control type of conditioning procedure with (A) and without (B) voluntary background abductor contraction. Note shorter latency and higher amplitude of after-contraction movement in A. Note also in A the higher level of abductor mean voltage EMG activity before than immediately after the conditioning procedure, even though the subject on both occasions held the arm in the same, slightly abducted position.