Contextual interference enhances vertical transfer of fine motor skill from upper to lower limbs

While contextual interference (CI) is known to facilitate motor learning, its role in promoting interlimb transfer-particularly from the upper to the lower limb-remains underexplored.

This study examined how different practice schedules (random vs. serial) influence the transfer of fine force control both horizontally (to the contralateral hand) and vertically (to the contralateral ankle).

Thirty healthy young adults (N = 30; Male = 21, Female = 9; Mean age: 21.9 ± 1.6 years) were divided equally into a random (RTG: N = 15) or serial (STG: N = 15) schedule group. Most participants were right-handed, with three left-handed individuals included across the two groups. Participants practiced a force-matching task with their non-dominant hand using either a random or serial schedule. Transfer effects were assessed in the contralateral hand and ankle at four target force levels (20-80 % of maximal voluntary contraction, MVC).

Both practice conditions improved force control in the contralateral hand (p < .05), indicating horizontal transfer. However, vertical transfer to the foot emerged only after random practice (p < .05) and was limited to moderate and high force levels. These findings suggest that the interaction between task difficulty and practice variability critically influences the extent and direction of interlimb transfer.

High CI practice promotes vertical transfer of motor skill when task demands are sufficiently challenging. These results highlight the importance of training structure in facilitating the generalization of motor control across limbs, offering practical implications for skill acquisition in both athletic and rehabilitation settings.