ARE CLUSTER SETS USEFUL FOR INCREASING MUSCLE MASS

INTRODUCTION

Traditional resistance training involves performing a prescribed number of repetitions which a given load in a continuous fashion with very little rest between reps. This leads to the development of tremendous fatigue, as metabolic by-products accumulate in the muscle while energy stores are depleted. The result of this is that the force development capacity of the muscle becomes steadily reduced to the point (if the set is taken this far) where failure occurs as the muscle can no longer overcome the load.

Cluster sets can be used to reduce the onset of fatigue via the insertion of a small intraset rest period that can vary from anywhere between 5-45s (based on the literature that has looked at cluster sets – really this period of rest can be as long as you like but eventually it will become an interest recovery period, although I’m not sure when this point actually occurs). Cluster sets have been shown to result in improvements for the following performance measures during a set:

• Higher peak force across the working set.
• Greater peak power output across the working set.
• Faster velocities being achieved across the working set for each repetition.

This should be no surprise to anyone as prescribing intraset recovery periods results in reduced fatigue being accumulated, as the short recovery periods allow for the buffering of metabolic by-products while energy stores are being simultaneously replenished. This allows the working muscle to maintain its output levels for longer periods of time. To my knowledge at the moment, there aren’t many longitudinal studies documenting the benefits of cluster sets over the traditional performance of sets (although there are some like Oliver et al¹), but from a theoretical perspective, this should all sound great for coaches who are trying to develop strength and power in their athletes. But, what about if you are trying to increase an athlete’s muscle mass?

INCREASING MUSCLE MASS WITH CLUSTER SETS

One thing that is becoming abundantly clear in the literature is that load is not a huge factor to consider when prescribing loading schemes to increase muscle mass. A consistent finding that is coming out of various research groups is that 80% 1RM is no more beneficial for increasing muscle hypertrophy than 30% 1RM^2,3. The caveat to this statement though is that whatever the load, the set should be taken to (or at least very close to) failure for muscle hypertrophy to occur.

A side note here is I’m sure there is a threshold for loading when trying to increase muscle mass – meaning it may be that loads as low as 10% 1RM are too low to stimulate muscle hypertrophy but 30% 1RM works just fine. Dankel et al.⁴ suggests that a set to failure with 30% 1RM lasts approximately 90s, which would obviously stress the fast glycolytic system and cause a large metabolic disturbance (which is a primary mechanism for stimulating muscle hypertrophy). From this perspective, it may be less about the load and more about the time under tension for the muscle as the athlete reaches failure.

So going back to the previous point, driving increases in muscle mass is very much about inducing fatigue in order to stimulate a muscle hypertrophy response. Reaching failure, regardless of load (to a point) not only increases the metabolic stress the working muscle is exposed to, but also facilitates the recruitment and stimulation of higher threshold motor units. Therefore, avoiding fatigue may be counterproductive if muscle hypertrophy is the desired outcome. This likely means that cluster sets, while hugely appropriate for strength and power development (theoretically at this point), may in fact impair the stimulus for muscle hypertrophy via reducing the overall fatigue that the muscle experiences⁵. Therefore, cluster sets may be considered an inferior approach to training when compared with traditional sets for increasing muscle mass.

The counterpoint to this perspective though is that cluster sets allows the athlete to handle higher loads, so instead of performing sets of 6 repetitions with 78% 1RM, an athlete may be able to perform sets of 6 with 82% 1RM with an intraset recovery of 30 seconds every 2^nd rep. Not much evidence exists for this approach at present as most studies that have investigated cluster sets have equated the training volumes between the cluster set and traditional set training groups. However, it may be that this approach to performing cluster sets would allow the athlete to perform the prescribed total reps at higher training intensities and therefore, achieve higher levels of fatigue than if a lower intensity were used. The benefit to this is, the athlete will likely increase maximal strength secondary to using higher training intensities. All the while, the athlete experiences similar levels of fatigue as the traditional approach, resulting in the same amount of hypertrophy as long as failure is reached for both protocols.

The only issue here is that, with the insertion of an intraset recovery, the training density is reduced. For example, if a 4×6 set-rep scheme using a 30 second intraset recovery after every 2 repetitions was prescribed, the working set would last 60 seconds longer than a continuous approach. Ten working sets (likely across multiple exercises) using this approach would obviously result in the training session taking 10-minutes longer if all other variables are equal (i.e. interest rest periods, time under tension, etc.). With these 10 minutes, the athlete could have performed more working sets if a continuous approach to performing sets was adopted instead of the cluster set method. In such case, more training volume may lead to greater increases in muscle hypertrophy, signifying the superiority of traditional sets over cluster sets.

However, again, it’s not that simple as a threshold of training volume likely exists where more sets doesn’t necessarily lead to more muscle mass⁶. So in this instance, as long as the volume threshold is crossed, muscle hypertrophy will be equally stimulated with either approach.

SO WHERE DOES THIS LEAVE US?

I would suggest that the current evidence available indicates that cluster sets is probably no better than prescribing the traditional approach to performing sets for increasing muscle mass. This is likely the case only if muscle mass is the sole objective. In fact, from a logistical perspective, cluster sets may be less useful than the traditional sets, as it takes longer to complete the same number of sets with the addition of intraset recovery periods.

However, athletes are rarely seeking to increase muscle mass with no regard for improving maximal strength. In most cases, they are seeking to increase muscle mass while developing their maximal strength. In such instances, cluster sets may prove valuable as they would allow the athlete to perform sufficient training volume to stimulate muscle hypertrophy, while also using the high loads necessary to increase maximal strength. Charles Poliquin terms this type of approach functional hypertrophy training, where muscle mass increases along with maximal strength. Table 1 provides an example of a training programme that incorporates cluster sets for developing functional hypertrophy.

Table 1. Example of how cluster sets may be incorporated into a training programme aimed at increasing functional hypertrophy.

 

For many (most) athletes, this would seem desirable and may present as a better method than performing traditional sets in the general preparatory phase, as two birds are hit with the same weight training stone. Furthermore, if higher loads are more useful for hypertrophying the fast-twitch fibres (which, to my understanding, the jury is still out on this concept), cluster sets would again present as an optimal strategy for increasing the size of type II fibres via the prescription of higher training intensities. This is especially the case for athletes who want to avoid increasing the size of type I fibres, which has been theorised to result in decreased muscle contraction velocities. This potentially occurs due type I fibres contracting at slower rates than type II fibres and therefore, impairing type II fibres capabilities to shorten the muscle at high velocities, as they create a “dragging” resistance that type II fibres must overcome.

SUMMARY

Cluster sets are extremely useful for increasing the force, velocity and/or power outputs during a working set when compared to the performance of traditional sets. However, there use for increasing muscle mass may be limited, if they reduce the overall fatigue a muscle is exposed to. As cluster sets do allow for higher training loads to be used, it may be that they allow for muscle mass to be increased to the same level as the traditional approach, while concurrently developing maximal strength with the incorporation of higher training loads being lifted

REFERENCES.

1. Oliver, J.M., Jagim, A.R., Sanchez, A.C., Mardock, M.A., Kelly, K.A., Meredith, H.J., Smith, G.L., Greenwood, M., Parker, J.L., Riechman, S.E. and Fluckey, J.D., 2013. Greater gains in strength and power with intraset rest intervals in hypertrophic training. The Journal of Strength & Conditioning Research, 27(11), pp.3116-3131.
2. Mitchell, C.J., Churchward-Venne, T.A., West, D.W., Burd, N.A., Breen, L., Baker, S.K. and Phillips, S.M., 2012. Resistance exercise load does not determine training-mediated hypertrophic gains in young men. Journal of applied physiology, 113(1), pp.71-77.
3. Schoenfeld, B.J., Grgic, J., Ogborn, D. and Krieger, J.W., 2017. Strength and hypertrophy adaptations between low-versus high-load resistance training: A systematic review and meta-analysis. continuum, 19(20), p.21.
4. Dankel, S.J., Jessee, M.B., Mattocks, K.T., Mouser, J.G., Counts, B.R., Buckner, S.L. and Loenneke, J.P., 2017. Training to Fatigue: The Answer for Standardization When Assessing Muscle Hypertrophy?. Sports Medicine, 47(6), pp.1021-1027.
5. Joy, J.M., Oliver, J.M., McCleary, S.A., Lowery, R.P. and Wilson, J.M. Power output and electromyography activity of the back squat exercise with cluster sets. J Sports Sci, 1:37–45. 2013.
6. Amirthalingam, T., Mavros, Y., Wilson, G.C., Clarke, J.L., Mitchell, L. and Hackett, D.A., 2016. Effects of a Modified German Volume Training Program on Muscular Hypertrophy and Strength. Journal of strength and conditioning research.