If you put your fingers across the 5V track and gnd on the PCB, even though your power supply can output 5A, the current through you will be regulated by OHMS LAW.
V = I * R
Voltage across a resistor = Current through the Resistor * The value of the resistor.
If you rearrange the equation.
I = V / R
So the current that will flow through you is;
I = 5 / Body resistance.
The resistance between my adjacent fingers is 25 MOhms at the moment.
I = 5 / 25,000,000 = 0.0000002A or 0.2uA.
Using this table;
From here;
https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html
The level is well below the "Threshold of Sensation".
However if you short the 5V PCB track to gnd with a short circuit, you may not feel it but your PCB will probably physically suffer.
Tom... 
