The effects of unilateral hand contractions on conscious control in early motor learning

Objectives: Hemisphere asymmetry can be influenced by hand contractions. Brain imaging studies have indicated that pre-performance left-hand contractions may reduce verbal-analytical engagement in motor planning, whereas pre-performance right-hand contractions may increase verbal-analytical engagement in motor planning. This study examined whether a pre-performance left-hand contraction protocol reduced verbal-analytical engagement during practice of a golf putting task, thereby causing implicit motor learning. Method: Forty-eight golf-novices were randomly allocated to left-hand contractions, right-hand contractions or no hand-contractions (control) groups. A line bisection task was conducted as a manipulation check of whether hemisphere asymmetry occurred. All participants practiced a golf putting task, with their allotted hand contraction protocol performed for 30 sec before every ten putts. Thereafter, participants completed two retention tests (blocks of single-task putting) before and after one transfer test (a block of dual-task putting). Different objective and subjective measures of verbal-analytical engagement were collected. Golf putting accuracy and kinematics were assessed. Additionally, mood-state as a function of hemisphere asymmetry was measured. Results: The line bisection task did not reveal a hemisphere asymmetry effect of the different hand contraction protocols. All groups equally improved during practice; however, the no hand-contraction (control) group showed better performance during both retention tests compared to left-hand and right-hand contraction groups. All groups performed worse in the dual-task transfer test. The objective and subjective measures of verbal-analytical engagement revealed no effect of hand contractions. General mood-state decreased for all groups from pre- to post-practice. Conclusion: Unilateral hand contractions prior to practicing the golf-putting task did not affect performance differently from the no hand-contraction (control) group. However, hand contractions resulted in worse performance compared to the no hand-contraction group during the retention tests, and dual-task transfer performance disrupted performance in all groups. No differences in verbal-analytical engagement were evident. Consequently, left-hand contractions did not promote implicit motor learning. Possible explanations and recommendations for future studies are discussed.