Short-term interference in learning ballistic motor tasks: Refining the notion of specificity
Authors: Bugnon Matteo , Ruffieux Jan , Taube Wolfgang 
Published: February 2024

Introduction
Learning of an isometric ballistic force task (BT) can be impaired if it is followed by the learning of a visuomotor accuracy task (VMT) involving isometric contractions of the same muscles (Lundbye-Jensen et al., 2011). This phenomenon, known as retrograde interference, is thought to occur because the memory trace created after learning the BT is affected by the activation of similar neural circuits involved in the VMT (Lundbye-Jensen et al., 2011). However, it remains unclear how the contraction type involved in the two motor tasks influences potential interference effects. The aim of this study was therefore to compare the influence of a VMT involving dynamic position control or isometric force control on short-term retrograde interference in a previously learned isometric BT involving the same muscles.
Methods
45 participants were randomly assigned to one of 3 groups. Participants started by learning an isometric BT involving the wrist flexors of the non-dominant hand. Participants in the first two groups then learned a VMT involving dynamic (VMTDynamic group) or isometric (VMTIsometric group) contractions of the same muscles, while participants in the third group took a break (control group). Finally, participants completed the BT retention test. Each BT training consisted of 35 trials in which participants were asked to achieve the highest rate of force development (RFDmax). The VMT training consisted of 50 trials in which participants were asked to follow a curve with a cursor. Position of the cursor was linked to the wrist flexion/extension angle (VMTDynamic) or the isometric force produced (VMTIsometric). Interference was quantified by comparing RFDmax between the end of the initial training (POST) and the start of the retention test (RET).
Results
A mixed design ANOVA revealed a significant interaction effect (F(2, 40) = 3.87, p = 0.029). Post hoc corrected paired t-tests showed a significant decrease in RFDmax for the VMTIsometric group between POST (2,524 ± 1,144 N/s) and RET (1,960 ± 921 N/s). In contrast, performance of the other two groups did not change (VMTDynamic group: 2,679 ± 1,321 vs. 2,499 ± 1,278 N/s; control group: 2,489 ± 1,005 vs. 2,334 ± 1,013 N/s).
Discussion/Conclusion
Interference was only observed in the VMTIsometric group, suggesting that the same type of contraction must be involved in the VMT and BT for short-term retrograde interference to occur. It is known that the neural control of isometric contractions is different from dynamic contractions (Duchateau & Enoka, 2016). It can therefore be speculated that the resulting reduction in neural competition between the motor tasks was sufficient to prevent interference in the VMTDynamic group. In conclusion, for retrograde interference to occur, not only must the same muscles be involved in both motor tasks, but they must also perform the same type of contraction.
References
Duchateau, J., & Enoka, R. M. (2016). Neural control of lengthening contractions. Journal of Experimental Biology, 219(2), 197-204. https://doi.org/https://doi.org/10.1242/jeb.123158
Lundbye-Jensen, J., Petersen, T. H., Rothwell, J. C., & Nielsen, J. B. (2011). Interference in ballistic motor learning: specificity and role of sensory error signals. PloS One, 6(3), Article e17451. https://doi.org/https://doi.org/10.1371/journal.pone.0017451