Lisa and rachel want to determine their muscular endurance, but they don't have access to a gym or any weight-lifting equipment. what can they use?

They can use gallon jugs on a pole or sand bags on a pole 

Rocks are always available.

They can use any measure they like as long as then can quantify it, and they can come up with an experimental design (i.e., they each take turns seeing if they can lift sequentially heavier rocks until one of them can't) that eventually turns up a difference in the measured variable.

Lifting and pull ups

Being unsanitary and unhealthy