Cluster Sets
What the cluster are we talking about here? Cluster sets, baby. This old training scheme seems to be poking it’s beautiful head back into gyms all over, and we are here for it. The difference between now and when it first came around in the 70’s though, is the loads of research proving it works. With this post, I will cover the what (are they), the why (they work), and the how (to implement). So without further adieu, let’s dive in to the world of cluster sets.
Cluster sets first came around back in the 1970’s, when Carl Miller wrote about how they can increase your time under tension. Today, time under tension is more commonly seen in tempo lifts (2-3 second descents, for example) or pause lifts (maintaining an isometric contraction between the eccentric/concentric portions - the up and down). It’s no secret that time under tension plays an important role in attaining a hypertrophic response to muscle fibers, and that cluster sets do in fact increase time under tension, but they also have so much more to offer. Cluster sets prove to be an appropriate scheme to improve neural drive, decrease mechanical fatigue, and maintain velocity and power output with each repetition.
How they differ from traditional sets (3x10, 3x12, 4x10, etc.), is that traditional sets focus on moving a constant load during consecutive repetitions with a long rest break at the end of each set (180-300 seconds, for example). Cluster sets, on the other hand, utilize rest breaks within the set, as well as the normal rest between sets. The rest breaks within the sets are shorter (20-60 seconds), but allow energy stores to replenish prior to the next round of reps which we will get into later. Confused? No worries, here’s a quick example:
Back squat of 30 total repetitions
Traditional set - 3x10 with a 3 minute break between sets
Cluster set - 3 sets of 4/4/2 clusters with 20 second rest breaks between each cluster, then followed up with a 3 minute break
4 reps, 20 second break, 4 reps, 20 second break, 2 reps = set
Now, that is just one example but hopefully it gives you the gist of how shorter rest breaks are included. There are several other ways to implement clusters which I’ll cover in the “how'“ portion later.
I get the idea can seem kind of silly, like “I’m not that tired, why can’t I just rep out all 10 instead of breaking them up?” You definitely can. My only question to you about it would be, “Are reps 8-10 moving as smooth as reps 2-5, or is fatigue starting to set in?” Chances are they are slowing down or possibly some are starting to lose form, and if they aren’t then you probably aren’t doing enough load to begin with. I’m not saying fatigue is the enemy, and in fact, some situations call for training into fatigue based on what your goals are. For the premise of maximal power output however, fatigue is less than ideal. When working to attain maximal power output, the main energy system used is the adenosine triphosphate-phosphocreatine (ATP-PCr), or anaerobic, system. Unfortunately, this system tends to max out after ~15 seconds, forcing the body to rely on aerobic systems to finish the set. This might not seem like all that bad of a deal, until you realize full replenishment of the ATP-PCr system can take up to 15 minutes based on the exertion of the exercise (Baker et al., 2010). So, not only are you utilizing aerobic systems to finish your first set, chances are you are not allowing your full anaerobic system to recovery which then affects your second set even earlier.
When you break up your sets into clusters of less than 5 reps, you allow your body to totally rely on ATP-PCr without tapping out the system completely. Then, you proceed to give it a mini-break which refills the tank a little bit (albeit not fully, but enough for the next cluster). These short bursts with the little pit stops allow your body to continue to push the weight with maximal to near maximal velocity for more repetitions. A study done by James Tufano in 2018 looked at how many repetitions at a set weight could be completed when using cluster sets vs traditional sets. He first identified the individuals maximal mean power output, and then set a threshold at 90% of that max for identifying “effective” repetitions as those that achieved a power output above that threshold using the velocity of the movements. On separate days, the individuals were to complete 6 sets of back squat at the same weight to maximal repetitions using traditional sets (no rests) and cluster sets (20 second rests after every 2 reps). The results were pretty significant in favor of the cluster sets.
The graph above is from that study, and it gives a good depiction of the benefit of cluster sets for not only improved capability for completing more reps in total, but also more effective reps. There is a way to twist this, since obviously a majority of programs (and definitely none of the programs we design) call for 50+ reps of back squat at max power output, as this shows how much more energy is being left in reserve by using cluster sets. So rather than using that energy to complete more reps, it can be used towards lifting more load instead. Instead of doing the same weight as you would for traditional sets, you can now increase the weight being used and complete the same number of total reps in cluster format. Let’s look at that with the example from before:
Back squat of 30 total repetitions
Traditional set - 3x10 at 185 pounds
Cluster set - 3 sets of 4/4/2 clusters at 200 pounds
Now you are completing the same total volume, but able to increase the total load. With allowing your body to rest and catch up in between clusters, the perceived difficulty will also be lower even though you are lifting more weight. This is all based around the premise that cluster sets limit fatigue’s ability to negatively impact your lifts when implemented appropriately. Key word, appropriately. It should go without saying, but the weight adjustment from traditional sets to cluster sets cannot be astronomical. A good rule of thumb for starting out is to shoot for around a 3-5% weight increase for your first set of clusters compared to the weight you would use for traditional sets. You can always increase the weight for the following sets if it is still too easy.
So we told you it works for improving volume capability in back squats, but what else is it good for? Well, fortunately Mr. Tufano took a look at that in a previous systematic review from 2017. The purpose of this review was to compare intra-set resting schemes (cluster sets) and traditional sets during various exercises. The findings were pretty overwhelming in favor of cluster sets. A few big takeaways after just 12 weeks:
Cluster sets resulted in greater power output in the bench press exercise and vertical jump
Power output during parallel back squat approached significance improvement in cluster sets
Absolute power difference in the bench press was greater with the use of cluster sets
Cluster sets resulted in greater increases in strength in the bench press and parallel back squat exercises
Hypertrophic changes were similar in traditional and cluster set training
In a nutshell, cluster sets result in greater strength and power, while also achieving similar hypertrophic responses as traditional sets. Sounds like a pretty sweet deal, but how should I start to incorporate cluster sets in my training? I thought you’d never ask.
First and foremost, I am not saying everyone needs to be doing cluster sets every workout. Not necessary. There’s a reason traditional rep schemes are still relevant - they work. I am simply providing you with an alternative design to break up any mundanity. When implementing cluster sets, I highly recommend keeping them just to your core exercises to start (squat, bench, clean, deadlift). Personally, for accessory work I believe there needs to be an element of fatigue to stress muscular endurance and stability so traditional sets work great for that. There’s really no set in stone way you have to do cluster sets. You can break up sets however you want, just as long as your utilizing very short rest periods when you do. Here’s a few more examples of ways you can break things up into clusters, regardless of the total number of reps:
Workout calls for sets of 12 reps
2 clusters of 6
2 clusters of 5, 1 cluster of 2
4 clusters of 3
6 clusters of 2
Workout calls for sets of 8 reps
2 clusters of 4
2 clusters of 3, 1 cluster of 2
4 clusters of 2
8 clusters of 1
Workout calls for sets of 5 reps
5 clusters of 1
1 cluster of 3, 1 cluster of 2
These lists are not all encompassing, obviously, but they do show how there’s really no set way in how you break up your sets. You can do clusters as big as 5-6 reps and as small as 1 rep. It doesn’t matter. Hell, the clusters don’t even have to remain the same throughout all of the sets. Do clusters of 3 the first set, then drop it down to clusters of 2 for the next set. The premise remains the same. Incorporate breaks throughout the set to improve overall performance and decrease the impact brought on by fatigue. Plain and simple.
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