Final answer:
Lugging occurs when the engine is operated below its peak torque, causing inefficiency and potential damage due to increased strain and possible overheating.
Step-by-step explanation:
Lugging occurs when an engine is operated below its peak torque for any length of time, which causes the engine to run inefficiently and can lead to damage or causing inefficiency and potential damage due to increased strain and possible overheating. This is commonly experienced when driving a vehicle in too high of a gear at a low speed whereby the engine does not have enough power to maintain speed, resulting in a noticeable shudder or vibration.
Operating an engine below its peak horsepower does not necessarily cause lugging; it is specifically the operation below peak torque that is problematic. Lugging the engine increases the strain, which can lead to overheating and potential long-term damage.