May 18, 2014

Clusters - How To Maximize Both The Load AND Time Under Tension

Take your pick, load or time under tension? BOTH!

The goal with any training program should always be to try and maximize the load, as well as the time under tension, at least if making positive strides towards putting muscle on your frame, burning fat off of it, or increasing your strength is the desired result. Obviously various goals will favor lifting a heavier load at the expense of time under tension, or favor a greater time under tension at the expense of the load, but the most effective techniques are those that capitalize on maximizing both.

Equally obvious is (at least it should be), the more weight you lift, and the more times you lift it, the better result you’re going to get regardless of the goal (obviously the amount of weight and reps performed is predetermined by the goal). This becomes problematic however, because the heavier the weight, the less reps that can be performed, therefore limiting the time under (near maximal) tension. Therefore, to lift the heaviest weights for prolonged times under tension, intermittent breaks are needed to allow for partial ATP regeneration, the clearance of metabolites, and neural recovery.

Do the math

When non-consecutive reps are chained together, which allows for more repetitions to be performed with a heavier weight than would otherwise be possible, the set is called a ‘cluster’. Performing sets in this manner is what allows you to maximize both the load, as well as time under tension.

By briefly discontinuing the set after each rep metabolite buildup is kept to a minimum, and the small amount of local lactate accumulation is allowed to dissipate, which mitigates the cellular shut down (inhibitory effect) of energy system enzymes that increase in direct proportion to the time in which the muscles are generating tension, thus enabling more reps to be performed before fatigue brings the set to an end.

Because oxygen debt is kept to a minimum, a longer recruitment of the fast twitch muscle fibers is permitted, enabling more weight to be used. However, you could modify clustering to prolong the time under tension and increase oxygen debt, forcing the recruitment of slower, oxygen efficient fibers.

Know your role

If the goal is to increase strength levels, then little matters more than recruiting and fatiguing the high threshold motor units. If the goal is to build muscle, the goal becomes recruiting and fatiguing the low threshold motor units in addition to the high threshold motor units. Basically you want to exhaust as many muscle fibers as possible, and clustering enables you to do this more effectively.

Strength emphasis

The eccentric repetition (muscle contracting against resistance while lengthening) should be emphasized if gaining strength is the goal, because it is during this phase of a repetition in which the high threshold motor units are preferentially recruited (although there is a lesser net total of motor units recruited, therefore totaling higher levels of stress per motor unit recruited). Because of this, more weight can be managed eccentrically.

Size emphasis

The concentric repetition (muscle contracting against resistance while shortening) should be emphasized if gaining size is the goal, because it is during this phase of a repetition that primarily produces the greatest amounts of metabolic waste/metabolite buildup/lactic acid (call it what you want). Because of this, both high and low threshold motor units will be knocked off.

What’s the problem?

The problem with enhancing the eccentric or concentric repetition is that it increases the total time under tension, and under traditional circumstances in which reps are performed consecutively, this dramatically limits the amount of reps that can be performed. If time under tension didn’t matter, it would be possible to slow down the tempo to promote a better result in terms of building muscle or gaining strength, while having no ill effect on the amount of weight that could be used, or the amount of reps that could be performed.

For example, if you can bench press 225 lbs. for ten reps, and no more, and each rep takes about 2 seconds to perform, you’re looking at a time under tension of 20 seconds. However, if you were to enhance either the eccentric, or concentric, or both, to at least 5 seconds, 10 reps would take anywhere between 50-100 seconds, an increase in time under tension by 250-500%, which is as close to impossible as anything I’ve ever heard of. Therefore, to expose your muscles to that kind of time under tension, the load would have to be significantly lowered, or small breaks between reps would be needed, and you’d simply add up the total time under tension that is accumulated over the course of the workout (which is the premise of clustering).

The rules of the game

As stated above, a longer eccentric (ex. 5 seconds) results in a greater amount of high threshold motor units being recruited, although a lesser amount of total motor units are recruited, thus prolonging the time under tension for the fast twitch fibers, which is ideal for strength gains. Due to the nature of the goal, longer rest intervals are needed between reps (ex. 30 seconds between singles) to allow for ATP regeneration, and neural recovery, as heavy weights are very neurologically demanding. Metabolite buildup/metabolic waste is less of a concern with eccentric enhanced clusters.

Also stated above, a longer concentric (ex. 5 seconds) results in a greater amount of low threshold motor units being recruited at the expense of the high threshold motor units, as motor units are recruited as needed, and if the weight is light enough that you can deliberately reduce the speed of the concentric phase of a rep, the high threshold motor units will generally be left out (as long as the muscles are allowed to relax between reps so the slow twitch fibers can get the oxygen they need, or else the fast twitch fibers will be forced into contributing), thus prolonging the time under tension for the slow twitch fibers. This combined with increased blood lactate, is ideal for building muscle (as it leads to non-functional hypertrophy, which at the end of the day is still hypertrophy). Due to the nature of the goal, shorter rest are needed between reps (ex. 10 seconds between singles).

*If the weight is light enough, try not to put the weight down, but rather hold at lockout, especially if you only plan to take 10 seconds between reps. Obviously if you are lifting heavy enough that you need a full 30 seconds to recover, your effort is best spent with the weight resting on the supports so you can reap the full benefits of clusters.

This is turning out to be one big cluster fuck

In theory clustering makes a lot of sense, but without parameters to practically apply them, it’s all for nothing, so here’s some guidelines to help anyone implement a cluster style of training into their current routine, or create a new routine from scratch based around their goals.

Normally 90-95% of maximum would result in 2-3, sometimes up to 4, consecutive reps being able to be performed. Because the whole point of clusters is to maximize both load, and time under tension, the goal would be to perform more reps with a given percentage of maximum than would otherwise be possible.

Starting at 90-95%, the goal is to complete 5-8 total reps with a 30 second pause between reps.

For every 5% reduction in weight, the total rep goal is increased by 2, and pause between reps is reduced by 5 seconds.

85-90% 7-10 total reps, 25 seconds between reps

80-85% 9-12 total reps, 20 seconds between reps

75-80% 11-15 total reps, 15 seconds between reps

*75-85% clusters are not limited to singles. Ex. 5 reps, rest 10 seconds, 3 reps, rest 10 seconds, 2 reps.

No more than one cluster per structure (or muscle) should be performed in a workout (or in a day if you choose to train more than once a day), as it is extremely physically and neurologically demanding, and the total sets should be limited to 3-5 only.

You’re on the clock

To add a density element to the equation, in which the goal is to perform a greater volume of work in a set amount of time, or the same amount of work in less time, you could do something like performing one rep every min for ten total reps, using your 3 rep max (3RM). The next time only take 45 seconds between reps, then 30 seconds, and eventually work your way down to 15 seconds between reps. Once you can complete ten reps with only 15 seconds between them, up the weight and do it again. Performing clusters in this manner can be a very effective way to see progress when making continual improvements in strength become increasingly more challenging and begin to taper off.

Double up

Even though clusters are generally reserved for lifting heavy weights for more reps than would otherwise be possible with the goal of increasing your strength, and building muscle, they can also be used to burn a ton of calories and improve work capacity (muscular endurance).

One way to do this effectively is to perform double the amount of reps that you would normally get by resting after each rep, until you get there (don’t be fooled, this is a lot easier said than done). For example, using your 10 rep max, pick up the weight and don’t stop until you get 20 reps. In fact, pioneering bodybuilders in the 50’s and 60’s largely credited their ability to pack on muscle by performing 20 rep ‘breathing squats’, in which you do not rack the bar until you perform all 20 reps, but rather let it rest on your back while you take a few breathes between reps, until you’re ready to go.

If it was easy, everybody would do it

Lifting heavy weights is not easy by any means. It’s both physically and mentally exhausting, but it’s an absolute necessity if you want to get the most out of your efforts. And while it is ideal to perform as many reps as you can with as high as an intensity as possible, sometimes things don’t go according to plan. This is why, even though it’s ideal to use the same weight throughout a set once you’ve begun, there’s no rule saying you can’t reduce the weight slightly each time to allow more reps to be performed. Doing so enables you to perform more reps, and while they may be done with a lower intensity than was intended, they will still be at, or near, your momentary maximum.

Drop it like it’s hot

Combining drop sets with clusters provides a bit of a twist to maximizing both the load and the time under tension. With traditional clusters, the chosen weight is generally heavy enough that performing multiple reps consecutively is not possible, but light enough that a brief rest period between reps permits for greater overall volume. Because it’s predetermined with a drop set that the weight is going to be reduced by a small percentage (5%) after each rep, a heavier weight than what would be used if performing a traditional cluster can be used to lead off the set.

For example, with a traditional cluster it wouldn’t be wise to use 100% of maximum, or your 1 rep max, for any of your sets because you wouldn’t be able to perform another rep with that weight even with up to 30 seconds rest (that’s why it’s your max). With a drop set cluster though, you could perform one rep with your max, reduce the weight, get back in there and perform another rep with what is now your momentary max (the most weight you can lift at the moment, given the circumstances), and continue in that fashion until completing the desired amount of reps. This way each and every single rep is a max effort, even though the reps at the end will be far lighter than if you started with a slightly lighter starting weight, and didn’t need to drop it from rep to rep.

With drop set clusters the rest should be as long as it takes to adjust the weight. While it may take less than 30 seconds to make those adjustments, the lack of rest is made up for by the progressively lighter loads used.

Break it down

For the visual learners, here’s a comparison between the traditional way of performing consecutive reps, with clusters, and clusters performed in a drop set manner:

Traditional set with 90% of max = 3 reps performed consecutively without rest

Cluster with 90% of max = 5 reps performed as 5 separate singles with a brief rest period between reps

Drop set cluster = 5 single reps performed with 100%* for 1, 95% for 1, 90% for 1, 85% for 1, 80% for 1

*Be smart and start with your 2 or 3 rep max if you don’t have a spotter.

As you can see, clusters, with or without the use of a drop set, enable you to maximize both the load and time under tension. In theory and ‘on paper’ this may make sense, and look easy, but make no mistake, this is likely one of the most challenging ways that there is to train. Anytime you combine extremely heavy weights with a great deal of time under tension, it’s going to take a toll on you mentally and physically. Those who are willing, and have the fortitude necessary to take on this type of training know all too well how effective it can be.

If you have any questions about clusters, or how to apply them to your training to build muscle or increase strength, feel free to contact me at I'm available for online consulting and personalized program design, as well as one on one training if you are located in the Greater Toronto Area (GTA).

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