Cluster Training: An advanced method to gain strength
There are many ways to change the training stimulus of a strength program. One of the most overlooked variables to manipulate is the rest periods within the sets themselves. Quite often, athletes and fitness participants will complete a set, rep to rep in a continuous manner. Depending on the number of reps and the exercise chosen, the set might take 30 seconds to 90 seconds. Now, there is nothing wrong with this methodology for certain exercises and for those with specific goals but I want to draw your attention away from this traditional approach to an approach we use at Human Motion to improve strength in our advanced clients.
The method is called Cluster Training
In this type of training set, a rest interval is prescribed between the reps. The rest interval can be anywhere from 10 seconds to 30 seconds. It can be prescribed after a few reps when levels of fatigue are reached, or between each and every rep, almost like the rest a basketball player would take between free throws. The load can be increased after the rest between each rep then decreased between the reps over a set to capitalize on postactivation potentiation. Or, perhaps, in the case of a relative strength exercise, the lever arm can be changed during the rest period to alter the biomechanics of the exercise and reduce or increase its intensity between each rep. There are a few different approaches one can use to employ this method of strength training. It is up to the skilled practicitioner to decide which approach he/she uses.
The physiology behind cluster training
The goal with cluster training is to improve the QUALITY of the client’s performance. The rest allows the client to produce force at a higher rate and may be beneficial in the development of “power-generating capacity” due to the decrease in repetition-induced fatigue (Haff et al, 2008).
It is known that Adenosinetriphosphate (ATP) and Creatine Phosphate (CP) are substrates, which provide energy for short-term exercise. ATP supports muscle contraction and CP is used under anaerobic conditions to rebuild ATP as it is needed and to replenish the body’s stores (Brooks et al, 1996). Creatine Kinase is a catalysing enzyme, which functions rapidly to re-establish the muscle concentration of ATP. Quantities of ATP and CP in a resting muscle are quite small therefore any utilization must be immediately replaced with an equivalent replenishment. If the ATP and CP utilization rate exceeds the restoration rate, exercise cannot continue very long. As CP stores are depleted, the body’s ability to quickly replace the spent ATP is seriously impaired. Fatigue is the result and the inability to produce a maximal muscular contraction.
In an exercising subject, the drop in ATP and CP appear to be related to the relative work intensity (Brooks, 1996). If the workload is more intense, there is greater the CP depletion, which leads to muscle fatigue (Brooks, 1996). ATP, however, will maintain its level until CP is greatly reduced. Thus, it is clear that CP depletion a significant factor leading to muscle fatigue at maximal effort.
Increases in blood lactate levels are also partially responsible for the fatigue-induced performance alterations (Haff, 2008). During short-term, high intensity exercise, a metabolite called lactate accumulates in the blood as result of lactic acid production exceeding its removal. The lactic acid dissociates, converting to hydrogen ions, causing a decrease in the pH. The hydrogen ions accumulate as a result of lactic acid production and can have several negative effects on the exerciser. Muscle contraction and energy production are adversely affected because of the subsequent decrease in ATP production. Hydrogen ions also displace calcium in the muscle fibre inferring with the coupling action of the actin-myosin cross-bridges making muscle contraction difficult.
Hypothetically, by incorporating a 20-30 second rest interval BETWEEN repetitions will result in some replenishment of CP, thus diminishing the stimulus for lactic acid and lactate production.
If strength and power gains are at the top of our client’s goal list, then cluster training can be a very useful method of training. In the research, it appears that cluster training has the potential to positively alter the strength training stimulus (Haff, 2008). It is most effective with pulling exercises like the deadlift, the clean pull, the power clean, the power snatch and variations of these lifts, where the client is most often working above 80% of their 1RM and where quality individual repetition power output is more important than total power output. Isn’t our goal as strength coaches to foster a training environment whereby our clients can perform work of high quality? Cluster training also work very well with ballistic-type exercises that have an accelerative profile such as box jumps.
The timely implementation of cluster training into a training program is key. If a client lacks muscle tone (hypertrophy), has a low work capacity (is deconditioned), lacks adequate hip mobility and trunk stability, then a more traditional approach to their physical development must be taken. And this might be taken for years! Cluster training should be used for the more advanced strength client as a means to reach new levels of performance. However, having said that, clusters work well when subjects are learning new skills (Bott, 2010). They provide, not only a means of physiological restoration, but a means of mental recovery to allow the newbie to focus on the task and facilitate learning.
For more information on cluster training protocols, email the coaching staff at Human Motion for a program: info@humanmotion.com
Works cited
Brooks, George, Thomas Fahey and Timothy White. Exercise Physiology: Human Bioenergetics and Its Applications. Mayfield Publishing: 1996.
Haff G. Cluster Training: A Novel Method for Introducing Training Program Variation. Strength and Conditioning Journal. Vol 30 N. 1, 2008.
January 29th, 2010 at 1:53 pm
Good blog. I got a lot of good info. I’ve been watching this technology for awhile. It’s interesting how it keeps varying, yet some of the core components stay the same. Have you seen much change since Google made their latest acquisition in the domain?
February 3rd, 2010 at 9:18 am
I’ve really enjoyed reading your articles. You obviously know what you are talking about! Your site is so easy to navigate too, I’ve bookmarked it in my favourites
February 3rd, 2010 at 10:57 am
I really liked reading your post!. Quallity content. With such a valuable blog i believe you deserve to be ranking even higher in the search engines
. Check out the link in my name. That links to a tool that really helped me rank high in google. This way even more people can enjoy your posts and nothing beats a big audiance 
February 5th, 2010 at 9:26 pm
This is some helpful info, thanks. Right now I’m focused on achieving shredded six pack abs. It’s my personal goal these days. Do you have any diet tips if the goal is to get a six pack as fast as possible? I’ve been told that egg whites, oatmeal, salmon, blueberries and broccoli are all important to incorporate into my diet. Anything else I’m not thinking of?
February 6th, 2010 at 7:43 pm
If you are looking for diet tips – talk to Cliff Harvey at cliff@humanmotion.com. He is our resident sports nutritionist and holistic health practitioner.
February 7th, 2010 at 12:32 pm
I Liked reading this post. Quite some usefull fitness info in it for me
. And after reading this i think you will really like the book Burn The Fat Feed The Muscle. To me this is like the health and fitness bible. Last year i lost almost 25 pounds and gained an inch on my arms in 12 weeks. What you describe here does resemble the book a bit, but there is so much more! I added the link in my name so you dont have to search for it 
. Again, nice post and i hope you keep it up!