Hello Alpha & welcome!
I think it's very hard to accurately determine anything like an average resistance of the human body.
So much depends upon the contact area, the individual's skin type, whether wet or dry, and so on that the resistance value can vary tremendously. Using normal meter probes grasped between thumb and first finger of each hand I can usually go from about 2 meg when dry and lightly gripped down to about 50K when damp and tightly held.
Increasing the contact area to something like that described by Al would certainly make the resistance much lower.
Most of the resistance is in the outer skin of the body, and direct contact with an open wound will lower the resistance considerably.
Some studies I've seen also suggest that the application of higher voltages results in a breakdown of the skin's resistance, and once that happens current flow increases dramatically. The couple of volts from an ohmmeter doesn't break down the barrier. In the extreme, readings from the electric chair indicate that with firmly attached electrodes the head to ankle resistance can sometimes be under 200 ohms once the high voltage has broken down the skin resistance.
