Cluster sets are a form of prescribing repetitions for exercises that incorporate short breaks between reps within a given set. When reading these you will find the repetitions of a particular set separated by a period (ex. 1.1.1, 2.2.2, 3.3.3). There are typically two different rest periods given. One for the duration taken between reps in the cluster, and one for the duration taken between sets.
Here’s an example of how a cluster set might appear in your program:
Back Squat 30X0; 1.1; rest 15sec between singles with the bar on the rack; 5 sets; rest 3mins between sets (build weight with each set)
In this example, the athlete would perform 1 back squat, place the bar on the rack for 15 seconds, and then perform a second rep.
Each set would have total of 2 reps with a 15 second break between the reps, with the goal in mind to potentially achieve a greater load for the two reps than if they were performed in one continuous set. Additionally, cluster sets can help train an athlete’s ability to repeat sub-maximal loads on short rest. Think about a situation in which you might want to power clean 80% of your maximum for many reps in a metcon. By training the power clean with clusters sets you can condition the body to get better at working at higher percentages on short rest.