Interference in ballistic task learning: refining the notion of specificity.

Ballistic task (BT) learning can be impaired when followed by learning an accuracy task (AT), a phenomenon known as retrograde interference. While for interference to occur, both tasks must involve the same muscles and movement direction (specificity), it remains unclear how the contraction type influences potential interference effects. This study aimed to compare the influence of an AT involving isometric force control (AT-iso) or dynamic position control (AT-dyn) on retrograde interference in a previously learned isometric BT. Forty-five participants first learned an isometric BT involving non-dominant wrist flexors. AT-iso and AT-dyn groups then learned an AT involving isometric or dynamic contractions of the same muscles, while a control group took a break. Finally, all participants completed a BT retention test. A mixed-model ANOVA revealed a significant interaction (p = 0.028), with a decrease in maximum rate of force development in the retention test observed only in the AT-iso but not in the AT-dyn or control groups. Therefore, a refinement of the notion of specificity is proposed: retrograde interference requires not only that both motor tasks involve the same muscles working in the same movement direction, but also that the type of contraction be very similar, if not identical.