Table 1 Overview of Kinarm exoskeleton parameters of the three bimanual coordination tasks

Ball-on-bar task (Level 1 and 2)

Task execution

Targets complete

Amount of successfully touched and held targets (without a ball drop in level 2)

Drops

Number of times the ball fell of the bar in level 2

Time to target

Mean time to reach a target from the moment it was visible to the moment it was touched (in s)

Ball speed

Mean ball speed throughout the level (in cm/s)

Unimanual

DH/NDH speed

Mean hand speed throughout the level (in cm/s)

DH/NDH speed peaks

Number of the hand's level-specific speed maxima, omitting those at the first and final data points

Bimanual: coupling

Mean bar tilt

Absolute value of the mean angle of the bar during the level (in radial)

Bar tilt standard deviation

Standard deviation of the level’s bar angle (in radial)

Bar length variability

Variation in bar length (in %)

Bimanual: interlimb

Hand speed difference

Differences between hand speeds divided by the mean of the hand speeds (in %)

Formula = \(\frac{\Sigma abs({S}_{DH}-{S}_{NDH})}{\mathrm{0,5}*\Sigma abs({S}_{DH}+{S}_{NDH})}\), with S = hand speed

Hand speed peaks bias

Relative bias in amount of hand speed peaks

Formula = \(\frac{{HSP}_{DH}-{HSP}_{NDH}}{{HSP}_{DH}+{HSP}_{NDH}}\), with HSP = hand speed peaks

Hand path length bias

Relative bias in hand path length

Formula = \(\frac{{HPL}_{DH}-{HPL}_{NDH}}{{HPL}_{DH}+{HPL}_{NDH}}\), with HPL = hand path length

Reaction time difference

For each successfully completed target in level 1, the mean absolute difference between both hands is calculated (in s). Formula = \(abs({RT}_{DH}-{RT}_{NDH})\), with RT = reaction time. This metric is not calculated in level 2 due to the considerable variability in reaction times due to the moving ball

Object-hit Task

Task execution

Target hits

The percentage of balls hit out of the total number of balls (in %)

Median error

The point during the entire challenge when 50% of all errors were made with regard to the whole task (in %)

Miss bias

X-value of the position indicating the direction of most errors. This parameter is calculated based on the number of misses in each of the ten bins with their weighted mean (in cm)

Formula = \(\frac{{\Sigma }_{i=1}^{10}{x}_{i}* {w}_{m,i}}{{\Sigma }_{i=1}^{10} {w}_{m,i}}\), with x_i = X-position of the ith bin, w_m,I = weight or the number of misses in the ith bin

Unimanual

Hits DH/NDH

Total number of hits with the dominant / non-dominant hand

Hand speed DH/NDH

Mean hand speed of each hand during the task (in cm/s)

Movement area DH/NDH

Movement area of each hand during the task (in cm²)

Bimanual: Coupling

Hand transition

Absolute x-value of the subject’s preference for using one hand over the other in the workspace (in cm). Larger value indicates a more shifted representation of the midline (in cm)

Formula = \(\left(\frac{{\Sigma }_{i=1}^{10}{x}_{i}* {w}_{h(DH),i}}{{\Sigma }_{i=1}^{10} {w}_{h(DH),i}}+\frac{{\Sigma }_{i=1}^{10}{x}_{i}* {w}_{h(NDH),i}}{{\Sigma }_{i=1}^{10} {w}_{h(NDH),i}} \right)/2\), with x_i = x-position of the ith bin, w_h(DH/NDH),i = weight or the number of hits of the DH/NDH in the i^th bin. [14]

Hand selection overlap

Percentage that captures effectiveness of using both hands (i.e. hit balls with both the dominant and non-dominant hand) (in %). Calculated by the sum of the hand changes for each bin divided by total number of hits

Bimanual: Interlimb

Hand bias hits

Bias in hits between hands divided by the total sum of both hands. Formula = \(\frac{{H}_{DH}-{H}_{NDH}}{{H}_{DH}+{H}_{NDH}}\), with H = hits

Movement area bias

Bias in mean movement area between hands divided by the total sum of both hands

Formula = \(\frac{{A}_{DH}-{A}_{NDH}}{{A}_{DH}+{A}_{NDH}}\), with A = movement area

Hand speed bias

Bias in mean hand speed between hands divided by the total sum of both hands

Formula = \(\frac{{S}_{DH}-{S}_{NDH}}{{S}_{DH}+{S}_{NDH}}\), with S = hand speed

Circuit task

Task execution

Error

The average surface between the cursor trajectory and the midline of the track (in cm²). [25]

Velocity

Average vectorial velocity of both hands (in cm/s). [25]

Skill

Measure of ideal accuracy (lower error) and speed, by dividing the velocity measurement with the error parameter. This value is multiplied by 1 cm/s to eliminate its dimension. Higher skill values are associated with more accurate movements and/or higher movement speed. [25]

Bimanual

Bimanual coordination factor

Calculated by dividing the minimum value between the absolute values of each hand by the hand’s vectorial velocities. When the child was only using one hand, the score was adjusted by using a penalty. The score ranges from 0 to 0.7, where a lower score indicates a more sequential movement of both hands. [25]

Formula = \(\frac{\mathrm{min}(\left|{V}_{x}\right|,\left|{V}_{y}\right|)}{\sqrt{{v}_{x }^{2}+{v}_{y }^{2}}}\), with v_x/y = absolute value of the horizontal/vertical hand velocity. [25]