Cluster training involves breaking individual sets down into smaller pieces – or clusters – with a short rest period in between them. By employing repetitions in clusters we can effectively ‘cheat’ a set by performing more reps at a higher intensity than we would normally be able to. In the first part we’re going to have a look at how clusters work and why you may want to use them in your training.
Chances are that you’ll know I’m a big fan of training density to elicit adaptation. Whilst density is somewhat similar to volume, it has an added dimension – intensity. Think of density as the amount of repetitions within a given training zone. Compare a workout with 3 sets of 10 to a workout with 10 sets of 3. Using my ‘magic’ formula, we can calculate that 30 reps at 12RM has a density of 2.5 whereas 30 reps at 6RM has a density of 5. Same volume, twice the density! Cluster training is a fantastic and efficient method to employ to increase training density.
How Clusters Work
There are many subtle variations, as we’ll discuss in the next instalment of this article, but the key to the cluster training is the rest in-between repetitions. Let’s take an example of a single set of 6 repetitions. In a traditional set you’ll complete your 6 reps and then rest for a few minutes. In an example of a cluster set, you’ll perform a mini-set of 2 reps, rest 15 seconds, perform 2 more, rest 15 seconds, and then perform the final two. The rest in-between clusters may only be 15 seconds but it has a significant effect on recovery. Performing the set this way means you can either increase the intensity of exercise (i.e. from 6RM to around 4RM in the example) or reduce the rest period in-between sets and possibly perform a set or two more.
Clusters for Strength Training
Lots of density in the magic ≥6RM zone = strength gains. That’s a good looking equation isn’t it?! Lots of triples at 6RM work well, as do singles at 3RM. Note that we shouldn’t be going to failure on any of these sets; the density is enough is elicit adaptation. Pushing it to failure will drain our old friend the central nervous system (CNS) and will be counterproductive for us in the long run. I wouldn’t recommend going above 3RM either; once again it’s a bit too taxing on the CNS.
The other great thing about inter-repetition rest intervals is that they help reinforce good technique. Cluster training allows you to the time to set-up and focus on the performance of each cluster, giving each repetition a higher level of perceived importance.
Clusters for Power Training
Research suggests that if we want to improve power production then we need to train at ≥90% of max power output. When we perform traditional sets of power exercises, such as Olympic lifts or jumps, power output will gradually decline throughout the set as we begin to fatigue. Clusters give us that little bit of recovery that allows us to stay in that crucial power training zone (Haff, et al., 2008) whilst once again reinforcing good form.
Clusters for Hypertrophy
There are three key factors that are responsible for hypertrophy; mechanical tension, muscle damage, and metabolic stress (Schoenfeld, 2010). Knowing this, there’s two ways we can go with clusters for hypertrophy.
Firstly, with cluster training, it’s possible to prescribe the same amount of overall time-under-tension but perform reps at a higher intensity. This means we increase mechanical tension and the resultant potential for muscle damage, although this method is likely to reduce the degree of metabolic stress. The higher intensity means we’re hitting more of those Type II fibres which are more facilitative to hypertrophy.
Secondly, we can perform more repetitions at a given intensity. There’s a bit of variation in the methods by which we can do this, but the premise is the same – increase the overall time-under-tension. This way we increase mechanical tension and potential damage, and depending on the cluster method employed, possibly induce a greater degree of metabolic stress.
So there’s the background on clusters wrapped up, next time we’ll look a few different ways of incorporating cluster training into your training!
Haff, G.G., et al., (2008). ‘Cluster training: a novel method for introducing training program variation.’ Strength and Conditioning Journal, 30 (1), p.67-76.
Schoenfeld, B.J., (2010). ‘The mechanisms of muscle hypertrophy and their application to resistance training.’ Journal of Strength Conditioning Research, 24 (10), p.2857–2872.