"Weight" of humans is a static variable as it is more of a force exerted by your body mass (not a continuously variable parameter) on the ground reference.
But when you exert strength to do something/anything, a component of "force" acts on the object in the direction of applied force, and in this case, depends on the force applied by your extremities on the same.
Let's consider a test case - that of pulling a mass "m" with a velocity "v" horizontally at the ground level. Then the force that you have to overcome is the frictional force b/w the object and the ground apart from the inertia. But when you do the same on an incline (inclined at an angle "theta", say), you also have to overcome "m times g times sin(theta)" the component of the weight of the object that is acting against you, making your job harder
. This is where you have to apply more "strength" or force. Keep in mind though, that there indeed needs to be a "minimum" force applied to move the object, e.g. a toddler couldn't move a suitcase whereas an adult could.
So, for your research, you could consider test cases where you exclusively vary weights (i.e. masses) of objects and then find out how they relate to the strength (force) needed to overcome those. You could also use different control variables like smoother surfaces, inclines etc.