Table 1.

Summary of the results

Manipulation	Coupling of the thumb and VF normal forces (grasping synergies)	Internal force–manipulation force (acceleration) coupling
Parallel
VV	Symmetric	Positive
HH	Symmetric	Positive (the internal force increases   slightly with the acceleration magnitude)
Orthogonal
VH	Anti-symmetric	Inverted-V pattern (symmetric)
HV	Depends on the frequency.	Depends on the frequency.
	Approximately anti-symmetric   at high frequencies	At high frequencies an asymmetric   inverted-V pattern with the peak at 1 g
Diagonal
DV	Symmetric	Positive
DH	Anti-symmetric	Positive (for the selected direction   of the coordinate axes)