[Ivan Juki? is finishing his Master’s degree at the University of Zagreb, Croatia where he also works as a personal trainer and S&C coach for soccer. He is currently an Applied Sport Science Intern at Athletic Lab.]

Training variations are essential because they stimulate recovery and adaptation, the avoidance of overtraining, long-term phase potentiation, and an elevation in performance outcomes (Plisk & Stone, 2003). Variation can be introduced into a periodized training program in many ways. Some typical examples of training variations that can be employed when designing a periodized program are manipulations of the overall training load, number of sets, number of repetitions, set configurations, and the exercises selected. These potential methods for introducing training variation allow the strength and conditioning professional a means for introducing novel stimuli into the training program. Hodges et al. (2005) suggest that the introduction of novel stimuli allows a more rapid gain in performance and that the more familiar the individual is with the task, the slower the overall gains in performance are. Therefore, it is essential that the strength and conditioning professional employs variations in the overall training program design in order to maximize the training outcomes. This is especially true for advanced and elite athletes.

One often overlooked method of employing variation to the training program is the manipulation of the structure of the set being employed. Traditionally, the configuration of a set requires the athlete to perform each repetition in a continuous fashion where no rest is taken in between each repetition of the set (Fleck & Kraemer, 1997; Haff et al, 2003; Stone & O Bryant, 1987).

Cluster loading, sometimes termed inter-repetition rest training, describes a training system whereby the rest periods are manipulated, breaking sets into small clusters of repetitions (Haff et al, 2008; Lawton et al, 2004; Lawton, Cronin & Lindsell, 2006).

Figure 1 – Here we can see the different setup of the training methods

 

Cluster sets can be used for a variety of physical qualities with the main ones being hypertrophy, strength, and power. With that being said, let’s talk about benefits that you can get with this training method.

We heard a lot of times that to gain size, we have to sacrifice power. Mentioned goes hand to hand with old belief that only low load – high rep work can increase your muscle size and that only high load – low reps can get you stronger. Both of these statements were debunked for a while now so everyone should know that you can get bigger with both approaches. Volume or better to say the amount of high quality work being done is king for hypertrophy. When volume is matched, gains in muscle size are similar regardless of the rep range and intensity used, as long as sets are taken near failure (or failure) (Morton et al, 2016; Schoenfeld et al, 2010; Schoenfeld et al, 2014; Schoenfeld et al, 2015; Schoenfeld et al, 2016). Basically, do more volume, gain more size as long as you are recovering well from your sessions.

Hypertrophy is gained by pairing mechanical tension and metabolic stress for a high volume. It shouldn’t matter if you do sets of 10 at 70% or sets of 3 at 70%. Like we said, if the volume and intensity are matched, gains should be similar.

Back to the first belief that was coming mainly from the bodybuilding world; it is true that over the course of a set, the velocity of contraction decreases (Izquiredo et al, 2006). Power is force, multiplied by velocity, this means power also decreases with each repetition. Because of this, a lot of coaches are “afraid” of hypertrophy and weight room in general. Every coach wants their athletes to be fresh and powerful so the reason why they freak out when they hear about power and velocity decrement is obvious.

In high-volume resistance training usually used for hypertrophy goals, there are large reductions in movement velocity and power output within sets and across multiple sets (Gorostiaga et al, 2013; S nchez-Medina & Gonzalez-Badillo, 2011). As evidence, S nchez-Medina et al (2011) reported a 46% reduction in mean velocity across 3 sets of 12 back squat repetitions performed to failure with 5 minutes of interset rest. Ultimately, traditional set structures that contain many repetitions result in accumulated fatigue, which may result in a reduced capacity to maintain a high velocity throughout a training session.

One potential explanation for the decrease in movement velocity, and ultimately power output, is the combination of reduced adenosine triphosphate (ATP) and phosphocreatine (PCr) availability (Gorostiaga et al, 2013; Gorostiaga et al, 2014; Gorostiaga et al, 2010). and increased lactate and ammonia accumulation that occurs when many repetitions are performed over multiple sets. With the implementation of a cluster method (I sound like a commercial now) you can neglect power and velocity decrement throughout sets because the phosphagen system appears to be able to meet the energetic demands of the exercise. Specifically, a maintenance of ATP and PCr availability enables movement velocity to remain near maximal. In fact, cluster training has already been shown to diminish lactate buildup in comparison with traditional continuous training (Gorostiaga et al, 2013; Gorostiaga et al, 2010; Moir et al, 2013). Finally, metabolic stress is the result of the accumulation of metabolites (particularly lactate, Pi and H+) and could be beneficial to promote hypertrophic adaptations (Schoenfeld, 2013).

When it comes to maximal and strength in general, studies that compared the cluster and traditional training method showed smaller strength gains (Drinkwater et al, 2005; Hanses et al, 2011; Lawton et al, 2004) or no difference (Izquierdo, 2006) between the two. Studies demonstrating smaller strength gains with cluster method used loads corresponding to 85% 1RM. At those intensities, this may very well be the case because increased recruitment of muscle fibers results in greater stimulation, particularly in the fast twich fibers, as measured by electromyography (EMG) techniques. The EMG activity has been shown to increase leading up to the sixth repetition in a 6RM (85% 1RM) bench press (Keogh, Wilson & Weatherby, 1999). However, when using a load around 70% or 10RM, Burd et al. (9) suggest that performing exercise with loads in this intensity range, maximal recruitment occurs at approximately 50% completion during the initial set, and performance of repetitions past this point results in reduced activation of fibers, which are considered quick to fatigue, primarily fast twich. Similar to previous studies comparing traditional with cluster method (Denton & Cronin, 2006; Lawton et al, 2004). Oliver et al. (2013) divided the number of repetitions performed in traditional hypertrophic training in half and equated rest using intensities ranging from 65 to 75% 1RM. This may have resulted in greater neuromuscular activation over consecutive sets compared with the traditional method, which may have contributed to the greater strength gains demonstrated in their study. However, they didn’t use cluster method in their particular study, they used density training method, which is beyond the scope of this article, so I doubt that comparison is worthy of anything.

Lawton et al. (2004) reported that bench press maximum strength was increased 9.7% using a traditional set structure compared with 4.9% using a cluster structure. Hansesn et al. (2011) findings regarding back squat 1RM are similar to those of Lawton et al. in that maximum strength increased by 3.7% more in the traditional group. Therefore, although cluster loading was still able to elicit a large training effect for maximum strength in a highly trained group, it seems that a traditional training structure is more effective for developing maximum strength.

Figure 2 – Clusters are heavy

The theoretical basis of cluster set structures, like we already said, lies in the short rest periods between clusters of repetitions allowing for metabolic recovery through the replenishment of muscular phosphocreatine, improving the quality of each effort and subsequent training adaptation. Although this metabolic recovery may be beneficial for the quality of movement and subsequent power adaptation, it seems that the strength adaptation may benefit from the build-up of metabolites. The literature suggests significant metabolite accumulation during high load strength training protocols (Crewther, 2004). The importance of this metabolite accumulation to adaptation is unclear (Folland et al, 2002; Ronney, Herbert & Balnave, 1994), however, there is some evidence that metabolic fatigue is an important precursor to both endocrine (Kraemer et al, 1998; Takarada et al, 2000) and neural (Takarada et al, 2000; Takarada & Ishii, 2002) responses to training. Therefore, it is possible that decreased metabolite build-up during cluster loading because of the recovery between clusters is counterproductive to strength development leading to improved strength adaptation from a traditional training structure.

The very best thing about cluster training method is power development. When the target is to develop muscular power it is widely recommended to perform low repetitions per set and ensuring appropriate rest periods to minimize fatigue and thereby maximize training effects (Baker & Newton, 2007; Cormie, McGuigan & Newton, 2011). Baker and Newton (2005) indicated that power output markedly decreases after 3 repetitions when using resistances that maximize power output (around 45 50% RM bench press) during the bench press throw exercise. Because of the short time under tension that occurs in only 3 repetitions, the metabolic accumulation could be negligible, and therefore, the neural fatigue would be the main reason for this performance impairment.

The study of Hansen et al. (2011) has analyzed the acute effects of different cluster configurations on ballistic exercises performance with low relative intensities (50%RM). This study examined the effect of 3 different cluster configurations (6 x 1 repetition with 12-second rest, 3 x 2 repetitions with 30-second rest, and 2 x 3 repetitions with 60-second rest) on the power output recorded during the jump squat with an absolute load of 40 kg (20%RM). They reported a significant decrease in power output from repetitions 4 5 for the traditional condition compared with the 3 different cluster configurations. Specifically, significant differences were found since the repetition 4 for the cluster set (12 seconds of rest between each repetition). Similar results were obtained in another study (Garcia-Ramos et al, 2015) for the cluster protocol. In comparison with the traditional protocol, in their study, movement velocity was significantly higher after repetition 4 at 30%RM and 40%RM and after repetition 2 at 50%RM.

A deciding factor regarding the effectiveness of cluster method in the augmentation of power development seems to be exercise intensity. Studies in which intensities used were close to the optimal load for power development (e.g., 80% 1RM power clean) in the respective exercise showed beneficial effects of cluster method on power output, while those working above the optimal load did not. Additionally, it has been shown that power output decreases when performing high-volume back squats using traditional sets (ie, performing repetitions in a set without intraset rest), but such decreases are ameliorated when using cluster sets (sounds like a commercial again I know). We can find a lot of studies on velocity and power decrement, however, These studies give an insight into the effect of fatigue on power production within single-set configurations i.e. to failure; which is not common to muscular power training programs that involve multiple set protocols.

Finally, Tufano et al. (2017) demonstrated that cluster sets allow us to handle greater external loads than traditional sets while resulting in similar mean and peak velocity decrement. With that being said, we can easily conclude that mentioned will also result in greater total training volume and time under tension while intending to move at maximal velocity. The additional intraset rest periods during cluster sets allowed subjects to successfully lift a greater external load for all repetitions conducted, resulting in 19% greater mean force, 15% greater total volume, and 26% greater time under tension than the traditional method. Example of the training protocols can be seen in figure 3.

Figure 3 – Example of how the clusters can increase your training volume from Tuffano et al. (2017)

All in all, we can say that if minimizing fatigue-induced changes in velocity is not of paramount importance, cluster-set structures can be designed to use greater loads for a given number of repetitions, resulting in greater total volume without sacrificing power. Although both a traditional structure and cluster structures could be prescribed for maximum strength, a traditional structure is likely to provide superior training outcomes. Cluster training does, however, present a viable training option for the development of power at light to moderate external loads and hypertrophy. Therefore, the practitioner should select the training structure that is best suited to the individual training goals of the athlete. If high load performance and maximum strength is the key training objective, then a traditional set structure should be used. If the development of explosive power and velocity at light to moderate loads or hypertrophy is regarded as a more important training goal, then a cluster structure may be preferable. It may be that an integrated approach that uses both loading schemes offers optimal training adaptation or at the very least offers athlete’s variation that can address training monotony. The last thing that we should think about before incorporating this method in our programs is time. Cluster method takes time, much more time than traditional training method. However, if we are not limited by time with our athletes (which I doubt, especially in team-sport settings) by all means, go for it. Like always, it’s not black and white; it’s about making a right decision at the right time with respect to all variables that come into play.

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