Assessing motor skill progression based on smoothness during integration of a new tool among hairdressers

Skill acquisition is traditionally assessed based on productivity measures, such as Movement Time (MT), which reflect task execution speed. However, movement smoothness may provide additional insights into skill progression by assessing improvements in movement execution. This study evaluated the evolution of both smoothness and productivity in hairdressing following a change of tool. Kinematic recordings of 14 professional hairdressers, novice users of Ringless Scissors [RS], were taken in the laboratory over four half-days of initiation and after 4.5 months of use in the hair salon. Three types of cuts were performed with Traditional Scissors [TS], then with RS. Smoothness [Number of Peaks (NoP); Log DimensionLess Jerk (LDLJ); SPectral ARC length (SPARC)] was assessed for an elementary movement sequence, spanning tool transport to the start of cutting. MT, representing the duration of these sequences, was assessed as a measure of productivity. After introduction of the RS, smoothness decreased and MT increased. With practice, both characteristics improved. After training, SPARC showed comparable smoothness between RS and TS for two of three cutting movements, while LDLJ and NoP remained higher with TS. After 4.5 months, smoothness improved further, with LDLJ and NoP approaching TS values. Although MT was significantly reduced, it remained higher with RS than TS after 4.5 months use in the salon. These results suggest that introduction of a new tool affects not only productivity - MT - but also movement quality - smoothness. The results presented highlight the relevance of smoothness measures in occupational contexts involving motor learning.