What is a "Top Set" vs a "Backoff Set" in Powerlifting?

A top set is typically the heaviest set of a given lift that an athlete will perform within a training session. It is usually programmed as the first working set so warmup sets are structured up to the session's top set. Top sets are commonly used in powerlifting and strength development to achieve a high-intensity level of stress and fatigue for the purpose of improving maximal strength. Lifting close to a maximal effort load allows the athlete to recruit more motor units, move weight more efficiently, and improve probability of achieving adaptation. A top set also provides insight into the athlete's daily strength fluctuations as the load can serve as the basis for selecting load intensity for backoff sets and accessory work. Backoff sets typically come after the top set. Weight is removed to decrease the intensity of the load on the bar -- however because a higher-intensity weight has already been lifted in the top set, backoff sets will likely still feel challenging due to the fatigue accumulated from the top set. Backoff sets can be programmed for many purposes such as technique development, achieving necessary volume, improving muscle mass, or targeting strength imbalances with a closely-related accessory movement.