So I'm working on this game, it's a sci-fi tabletop RPG based on the RuneQuest rules (where physical statistics generally have a numerical value between 3 and 18) and I'm trying to figure out a means of deriving the carrying capacity of a human; ie. how much weight a human can reasonably carry for a day's hike. The calculation I'm using for maximum lifting weight (derived from weight-lifting world records) is as follows:

Lift

(STR + (CON / 2)) x 10
This figure determines the absolute maximum weight (in Kg) a character can lift above their head.

Sadly my Google and Wikipedia-fu are not strong and I've found no figures for how much a human can carry for a day. Can anyone point me in a helpful direction? Or tell me how much an extremely fit person can tote over a long period?