Real World Data -- Loads

I recently read a newspaper article on the heavy loads carried by combat soldiers and the impact thereof.

The key point was that carrying loads of 100 lbs in combat on a regular basis -- even when the bearer is a young, physically fit male -- causes injuries. A USMC after-action-report finds that heavy loads limit the mobility of riflemen with tactical consequences.

Note how well this maps to the rule of 7; a 100 lb load is around 7 stones, and that is apparently beyond the max load that can be carried safely. It also hints at some possible mechanical consequences to heavy loads beyond speed penalties. Perhaps there is a risk of long-term ability score damage or other long-term consequences to carrying such extreme burdens in combat conditions.