Table 2. Dependant variables.

Label	Name	Definition	Computation
BFT	Ball flight time	Time duration between the throw of a ball and its consecutive catch
K	K-ratio	Proportion of time with the hand loaded (TL - i.e., with ball in hand) in a juggling cycle	with
DBT	Distance between throws	Euclidean distance between two consecutive points of throws in the vertical plane
ThVel	Throw velocity	Norm of the velocity vector at time of throw in the plane of ball flight
ThAngle	Throw angle	Angle of the velocity vector at time of throw in the plane of ball flight
FSI	Frequency synchronization index	Difference between the hand frequency and the metronome frequency
PSI	Phase synchronization index	Dispersion of the relative phase
DT	Dwell time	Percentage of phase locking episodes	with ɛ a limit value and Nsamples the number of values in a trial

We analyzed the within-trial standard-deviation of the dependant variables listed in this table. The first two variables (BTF, K) are used to assess the juggling performance in time. The third variable (DBT) addresses the spatial aspects of the coordination between hands in the transversal axis (DBTy) and in the vertical axis (DBTz). Two variables (ThVel, ThAngle) focus on the throwing, which is key to sustained juggling. Note that, though the juggling was performed in 3D space, ThAngle refers to the elevation angle in the plane of ball flight. The three last variables (FSI, PSI, DT) were used to assess the synchronization of the participant with the metronome. Hand frequency (Ωhand) was the inverse of the average period of time between two consecutive throws by the same hand. The metronome frequency (Ωmetronome) was the inverse of the period of the metronome.

In the equations of the computation column : T is the time ; Hx, Hy, Hz are the coordinates of the hand ; Bx, By, Bz are the coordinates of the ball ; indices specify the juggling events (i.e., catch, throw) ; d indicates the differential, so that dQ_throw is the differential of Q at time of throw ; L/R refers to the left/right hand ; ϕ is the relative phase between hand position along the vertical axis and the metronome.