Start-stop paradigm in motor learning: Higher vulnerability at task resumption in ADHD

Children with Attention-Deficit/Hyperactivity Disorder (ADHD) exhibit significant motor instability, yet the specific mechanisms remain unclear. This study introduces the "Start-Stop Paradigm" to investigate motor vulnerabilities at critical transition points: task initiation, continuation, and resumption after a break. Participants were 96 children aged 9 to 10 years (48 with ADHD, 48 typically developing; 48 boys, 48 girls). Re-analyzing data from a dart-throwing task, we found that children with ADHD demonstrated greater performance instability, with 12 out of 17 throw-to-throw transitions showing significant sequential dependencies (φ = 0.3-0.5), compared to only 8 in typically developing children. A pronounced "reverse hot hand" effect was observed at the block transition (resumption after a pause) in both groups, but it was more marked in the ADHD group. This indicates that resuming a task after a stop is a particular vulnerability. The Start-Stop Paradigm posits that children with ADHD struggle disproportionately with motor planning and execution at these transitions due to deficits in attention shifting, working memory updating, and motor parameter recalibration. These findings suggest that motor interventions for ADHD should be specifically tailored to stabilize performance at transitions, rather than focusing solely on overall practice volume.