There's an old saying that a chain is only as strong as its weakest link. That adage also applies to multi-joint movements. Indeed, multi-joint movements have a distinct disadvantage because they generally have a "weak link." When an athlete fatigues in an exercise it is because the smaller, weaker muscle becomes exhausted. This happens well before the larger and stronger muscle has received a sufficient workload. In an exercise like the lat pull-down, the biceps are the smaller muscle and, therefore, will fatigue long before the upper back. To solve this problem, we can utilize the Pre- Exhaustion Principle. The Pre-Exhaustion Principle employs what has been called a "double set": one single-joint movement followed quickly by a multi-joint movement. With the Pre-Exhaustion Principle, the idea is to "pre-exhaust" the muscles you are trying to work by first performing a single-joint exercise. In effect, this will bypass the weak link. The first exercise is followed quickly by a second exercise to bring into play other surrounding muscles which provide assistance to work the pre-fatigued muscle to a point beyond it's normal state of exhaustion. For instance, let's suppose that you want your athletes to exercise their upper backs using the Pre-Exhaustion Principle. The first thing they'd do is perform a single-joint exercise -- such as a barbell or a dumbbell pullover -- to pre-fatigue their upper backs. As soon as possible following the completion of that exercise, they'd perform a multi-joint movement -- like a lat pull-down or a seated row. That second set will employ their arms to assist their pre-fatigued upper backs to work to a degree of exhaustion that would normally be impossible. It should be noted that for maximum results, the second exercise should come as soon as possible following the completion of the first exercise. Too much time between the first and second exercises will allow the pre-fatigued muscle to gradually recover some of its original level of strength. If the muscle recovers too much, then you're back to where you started with the weak link still being the limiting factor.

This definition is in context to Fitness. See more contextual defintions for Pre Exhaustion.