The effectiveness of an exercise program depends on the acute program variables and how they are manipulated in order to drive a specific physiological adaptation. These program variables include choice of exercise, order of exercise, load/intensity, volume (sets/repetitions) and rest periods (Fry, 2004). For example, the number of repetitions, intensity, and rest periods within a set may be manipulated to alter the training stimulus.
It has been suggested that the introduction of a novel training stimulus results in a more rapid gain in performance, and that the more familiar an individual is to a stimulus the slower the gain in performance is (Hodges et al, 2005).
Consequently, this highlights the importance of variation within training program design in order to maximise training outcomes. This article will briefly introduce cluster sets and how they may be applied to offer a novel stimulus during resistance training.
When designing a resistance training program 2 types of set structures are most often used: traditional sets and cluster sets. Traditionally, a normal set requires the individual to perform each rep consecutively without any inter-repetition rest. Using this paradigm, the individual will accumulate a significant amount of residual fatigue throughout the entire set, thus resulting in a decrease in peak power output, maximum force application and technical proficiency as the set continues. This is as a result of the increased metabolic demand which appears to correspond with performance decline (Gorostiaga et al, 2010).
A cluster set differs by introducing short rest periods of between 10-45 seconds in between repetitions. In its simplest form the introduction of a 20 second rest in between each repetition of a 5 repetition set would create a basic cluster set that would allow for better repetitions to be performed throughout the entire set with a higher intensity (Fig.1.).
The beneficial effects of using a cluster set configuration would therefore allow the individual to perform each rep with the highest quality. This is an advantage for the development of power generating qualities as well as a higher volume of training being able to be performed at peak power output. The numerous benefits of using cluster set configuration described here suggest that cluster set design may be manipulated to achieve a specific adaptation.
Figure 1. (Haff, 2016; NSCA Conference Presentation)
This may also be relevant to hypertrophy training as it has been suggested that the adaptive response that stimulates muscle growth is more dependent on overall work output or volume load of the training session. Based on these assumptions, implementation of cluster sets appear to allow the individual to train at a higher intensity with a higher volume load therefore resulting in an increased training stimulus compared to the traditional set configuration (Tufano et al, 2017). This is a key factor for hypertrophy training (Kreiger, 2010).
However, the development of muscle growth is a complicated process that involves both mechanical and metabolic stress. With this in mind, the use of cluster sets may not be appropriate in eliciting significant metabolic stress and may not be as effective as traditional sets when trying to induce muscle hypertrophy (Girman et al, 2014).
The idea that greater training volumes result in greater muscle hypertrophy supports the idea that cluster sets may be an alternative method for muscle hypertrophy. However, if traditional sets and cluster sets are performed with the same intensity, it is likely that traditional sets would result in greater hypertrophy due to the increased physiological response.
When training volumes are equalised between traditional sets and clusters sets there is a blunted physiological response observed after cluster set performance resulting in lower lactate and hormonal response (Girman et al, 2014 & Oliver et al, 2015). This highlights that traditional sets may still be more effective for hypertrophy however, using a cluster set configuration during a de-load microcycle may allow for volume and intensity to maintained while the physiological response is decreased to facilitate recovery and adaptation.
Figure 2 shows how a traditional set to drive hypertrophy may be manipulated using a cluster set configuration to result in a greater volume of training performed at a higher intensity. This figure shows how 3 sets of 12 repetitions can be performed with approximately 80%1RM using a cluster set configuration whereas using a traditional set intensity would be around 60%1RM.
Figure 2. (Haff, 2016; NSCA Conference Presentation)
Maybe the most effective use of cluster sets would be in the development of explosive strength or power endurance. For example, Sahlin et al (1989) showed that a 15 second inter-repetition rest allowed force generating capacity to recover by approximately 80% enabling each repetition to be performed without a significant drop in velocity, therefore sustaining a higher intensity per repetition.
Longer inter-repetition rest will result in even greater maintenance of peak force output allowing more force to be applied during later repetitions within the set, allowing the athlete to perform the set with overall higher movement velocities - which are indicative of strength gains (Gonzalez-Badillo et al, 2014).
Lawton et al (2006) showed that using a cluster set configuration during a set of 6 heavy repetitions in bench press resulted in a 21-25% increase in power output compared to a traditional set configuration with the same load.
This may be even more relevant when performing technical exercises such as the olympic lifts. These exercises are programmed in an attempt to develop explosive strength and power however due to the technical proficiency required to perform, repetitions are kept low in order to maximise force and power output and to avoid injury. The inclusion on cluster sets when performing the olympic lifts may therefore allow an increased volume load to be performed at a give intensity.
Decreasing the rest between repetitions or clusters results in an increased physiological response and a shift towards strength or power endurance (Fig.3.). Whereas, allowing for more recovery time would be more beneficial if the focus was on maximal movement velocity or peak power output (Haff, 2016).
Therefore, rest periods can be manipulated to increase or decrease the physiological stress which can in turn be used to drive a specific training adaptation; the greater the number of repetitions performed in a cluster the longer the rest interval needed between clusters.
Figure 3. (Haff, 2016; NSCA Conference Presentation)
The limitations of using a cluster set configuration is the extended time required to complete a given training sessions. This may be problematic when working within a team sport environment when there is limited exposure time between the strength and conditioning staff and athletes.
In summary, traditional set configurations may still be more effective if the training outcome is hypertrophy. However, cluster sets may be implemented to introduce variation to the training program. The lower physiological response when implemented with hypertrophy training loads may allow volume and intensity to be maintained during a de-load microcylcle in an attempt to facilitate recovery and adaptation. The main benefits may be realised when the training focus is power development or strength endurance. Implementing cluster sets when focusing on these characteristics allow a maintenance of velocity throughout a working set which is indicative of strength and power gains, as well as allowing higher volume loads to be performed at a given intensity.
References
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Girman, JC, Jones, MT, Matthews, TD, and Wood, RJ. Acute effects of a cluster-set protocol on hormonal, metabolic and performance measures in resistance-trained males. Eur J Sport Sci 14: 151–159, 2014.
Oliver, JM, Kreutzer, A, Jenke, S, Phillips, MD, Mitchell, JB, and Jones, MT. Acute response to cluster sets in trained and untrained men. Eur J Appl Physiol 15: 2383–2393, 2015.
Lawton, TW, Cronin, JB, and Lindsell, RP. Effect of interrepetition rest intervals on weight training repetition power output. J Strength Cond Res 20: 172–176, 2006.
Haff, G., 2016; Bridging The Gap., NSCA Conference Presentation
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