Detection and analysis of experimental signals

The Bilateral Index (%) of MVC and RFD/PF = ((bilateral right value + bilateral left value)/(unilateral right value + unilateral left value)) * 100 were determined. The peak force (PF) of gripping was chosen as the highest force produced on the trials. The PF was normalized to the MVC of gripping and is expressed as a percentage of the MVC (%MVC). The peak RFD was calculated from the first derivatives of the force signals with a 32-point window width using chart 8.1.13. The RFD was shown as a percentage of MVC per second (%MVC/s). The normalized RFD was calculated by the RFD to PF ratio (RFD/PF) in each trial. In the PF, RFD, and RFD/PF, the mean of the 30 trials was used as the representative value for UL_R, UL_L, BL right-hand (BL_R), and BL left-hand (BL_L). The variability of RFD and RFD/PF was measured from the standard deviation for each participant across the 30 trials. Force errors were determined as the difference between the target force (30% and 50% of MVC) and PF in each trial (Fig 2). Three types of force errors were calculated: constant force error (CFE), absolute force error (AFE), and variable force error (VFE). When PF was greater or lower than the target force, the CFE showed positive or negative values, respectively. The mean value from the 30 trials was used as the representative value for UL_R, UL_L, BL_R, and BL_L in force intensity errors. The equations for CFE, AFE and VFE are as follows [17]:

where i indicates the trial number; X_i is the produced peak force for the ith trial; F is the target force level (30% or 50% of MVC); N is the number of trials, and M is the average peak force for the N trials.