Some loads are specified as part of the design criteria of a mechanical system.
Depending on the usage, some mechanical loads can be measured by an appropriate test method in a laboratory or in the field.
It can be the external mechanical resistance against which a machine (such as a motor or engine), acts.
For instance, a given car traveling on a road of a given slope presents a load which the engine must act against.
By shifting to a higher gear, one may be able to meet the requirement with a higher torque and a lower engine speed, whereas shifting to a lower gear has the opposite effect.