Objectives
Conscious engagement in movement control can influence motor performance. In most cases, the left hemisphere of the brain plays an important role in verbal-analytical processing and reasoning, so changes in the balance of hemispheric activation may influence conscious engagement in movement. Evidence suggests that unilateral hand contractions influence hemispheric activation, but no study has investigated whether there is an associated effect of hand contractions on verbal-analytical processing and psychophysiological activity during motor performance. This study was designed to examine whether pre-performance unilateral hand contraction protocols change verbal-analytical involvement and psychophysiological activity during motor performance.

Design
A repeated measures crossover design was employed.

Methods
Twenty-eight participants completed three hand contraction protocols in a randomised order: left, right and no-hand contractions. Electroencephalography (EEG) measures of hemispheric asymmetry were computed during hand contractions. A golf putting task was conducted after each protocol. EEG connectivity between sites overlying the left verbal-analytical temporal region (T7) and the motor planning region (Fz) was computed for the 3-sec prior to movement initiation. Additionally, electrocardiography (ECG) and electromyography (EMG) signals were analysed 6-sec prior to movement initiation until 6-sec after. Golf putting performance was obtained by distance from the target and putter swing kinematics.

Results
Contralateral hemisphere activity was revealed for the left and right-hand contraction conditions. During motor planning, the left-hand contraction protocol led to significantly lower T7-Fz connectivity, and the right-hand contraction protocol led to significantly higher T7-Fz connectivity than the other conditions. EMG, ECG and kinematic measures did not differ as a function of condition. Importantly, T7-Fz connectivity mediated the relationship between hand squeezing and motor performance (distance from the target).

Conclusion
The EEG results suggest that pre-performance unilateral hand contractions influence the extent of verbal-analytical engagement in motor planning, which in turn influences motor performance. However, the hand contractions did not influence cardiac activity, muscle activity or kinematics.