Relationship between correcting error and smoothness of movement in the process of motor learning

[Purpose] Improvement in the smoothness of movement is a motor learning outcome. This study sought to clarify the relationship between motor skills and smoothness of movement in motor learning. [Participants and Methods] We subjected 12 healthy adults to a task in which they had to learn the sensation of a load while standing up and sitting down. We attached triaxial accelerometers to the seventh cervical spine and the third lumbar spinous process of the participants prior to measurement. We took the measurements over two successive days and used absolute error and variable error as indicators of motor learning outcomes. In addition, we used entropy, calculated from the results of the power spectrum analysis of acceleration changes, as an indicator of the smoothness of the movement. [Results] In the test sessions, absolute and variable errors showed a significant reduction. Entropy also showed a similarly significant decrease, although the change in errors and entropy showed different transitions. [Conclusion] Qualitative indicators of motor learning captured an aspect of motor learning that one cannot capture by quantitative indicators. In the future, qualitative indicators will be necessary to judge the outcomes of motor learning.