Motor imagery (MI) training is often used to improve physical practice (PP), and the functional equivalence between imagined and practiced movements is widely considered essential for positive training outcomes.

We previously showed that a 5-week MI training program improved tenodesis grasp in individuals with C6–C7 quadriplegia. Here we investigated whether functional equivalence changed during the course of this training program.

In this descriptive pilot study, we retrospectively analyzed data for 6 individuals with C6–C7 quadriplegia (spinal cord injured [SCI]) and 6 healthy age-matched controls who trained for 5 weeks in visual and kinesthetic motor imagery or visualization of geometric shapes (controls). Before training, we assessed MI ability by using the Kinesthetic and Visual Imagery Questionnaire (KVIQ). We analyzed functional equivalence by vividness measured on a visual analog scale (0–100) and MI/PP time ratios computed from imagined and physically practiced movement durations measured during MI training. These analyses were re-run considering that half of the participants with quadriplegia were good imagers and the other half were poor imagers based on KVIQ scores. To investigate generalization of training effects, we analyzed MI/PP ratios for an untrained pointing task before (3 baseline measures), immediately after, and 2 months after training.

During MI training, imagery vividness increased significantly. Only the good imagers evolved toward temporal equivalence during training. Good imagers were also the only participants who showed changes in temporal equivalence on the untrained pointing task.

This is the first study reporting improvement in functional equivalence during an MI training program that improved tenodesis grasp in individuals with C6–C7 quadriplegia. We recommend that clinical MI programs focus primarily on vividness and suggest that feedback about movement duration could potentially improve temporal equivalence, which could in turn lead to further improvement in PP.