Hand–foot coordination is significantly influenced by motion direction in individuals with autism spectrum disorder

Generally, when individuals attempt to move two limbs rhythmically in the opposite direction (e.g., flex the left hand and extend the left foot along the sagittal plane), the movements tend to be instead performed in the same direction. This phenomenon, known as directional constraint, can be harnessed to examine the difficulties in movement coordination exhibited by most individuals with autism spectrum disorder (ASD). While such difficulties have already been investigated through standardized clinical assessments, they have not been examined through kinematic methods. Thus, we employed a clinical assessment scale in an experimentally controlled environment to investigate whether stronger directional constraint during the rhythmic movement of two limbs is more pronounced and associated with decreased movement coordination in individuals with ASD. ASD and typically developing (TD) participants were asked to rhythmically move two limbs either in the same or opposite directions. In addition, the coordination skills of participants were assessed using the Bruininks-Oseretsky Test of Motor Proficiency Second Edition (BOT-2). Subjects with ASD showed significantly stronger directional constraint than TD participants during the contralateral and ipsilateral movement of the hand and foot. According to the pooled data from both groups, participants who showed stronger directional constraint during these two movement conditions also exhibited poorer coordinated movement skills in the BOT-2. Furthermore, stronger directional constraint was associated with severe autistic traits. These results suggest that people with ASD may have difficulties in inhibiting the neural signals that synchronize the direction of inter-limb movements, thus resulting in coordination disabilities. Lay Summary Individuals with autism spectrum disorder (ASD) often exhibit difficulties in coordinated movements. We asked those with ASD and healthy participants to move two limbs (e.g., left hand and left foot) either in the same or the opposite direction. Results demonstrated that participants with ASD had more difficulties in counteracting the tendency of their hand and foot to synchronously move in the same direction. Our findings suggested that difficulties to suppress synchronized movements of the hand and foot result in coordination disabilities. ### Competing Interest Statement The authors have declared no competing interest.