Build Size & Strength With Isometric Co-Contractions: 4% Increase in Arm Circumference and ~20% More Strength With Less Than 10 Minutes of "Flexing" Per Week

Big guns without weights? True - the question yet remains: "How big?"

I am psyched and the reason is the advanced access publication of the results of the latest study from the Department of Sports and Life Science at the National Institute of Fitness and Sports in Kanoya, Japan (Maeo. 2013b).

Why? Well, it claims to solve two of the most urgent issues that keep our sedentary fellow men (and women ;-) from working out: The lack of equipment and the lack of time, exactly those two factors the average American and European slacker pleads as an excuse for not making the necessary, since potentially life-saving physical investments into "metabolic currency" (this is a term my good friend Carl Lanore uses to refer functional muscle mass).

"Big guns without weights? You're kiddin', bro!"

Actually the idea of using simultaneous voluntary contractions of antagonistic muscle pairs (aka co-contraction) to improve muscle strength in the absence of external apparatuses is not new. The voluntary co-con traction of elbow flexors and extensors you can see in the photo in the red "This is how it's done" box, for example, may look ludacris (imagine doing that at the gym), its efficacy is however backed by previous research and its working principle is as simple as ingenious: Biceps and triceps, i.e. elbow flexor and extensor, produce resistive forces that act against each other (Tyler. 1986), so that one muscle actually "trains" the other.
In their initial investigation into the effects of muscular co-contraction, the results of which have been published in the International Journal of Sports Medicine in July 2013 (Maeo. 2013b), the researchers have been able to confirm that the muscular activity that occurs during the voluntary co-contractions is a sufficient training stimulus for improving the strength capability of both muscles (Maeo et al. 2013a).

"In fact, previous studies that adopted co-contraction training for elbow flexors and extensors (Driss et al. 2013; MacKenzie et al. 2010; Maeo et al. 2013) found significant increases in the strength capability, as well as agonist electromyographic (EMG) activity during isometric maximal voluntary contraction (MVV) (MacKenzie et al. 2010; Maeo et al. 2013), of the two muscle groups. the previous findings cited above support the idea that co-contraction can be an effective training modality, which does not require any external apparatus, for increasing muscle strength." (Maeo. 2013b)

So, while we are pretty certain that "standing there and contracting your bis and tris" can increase muscle strength (learn how to build strength), there is a scarcity of evidence that would allow us to make reliable statements about the effects of voluntary muscular cocontractions on muscle size (learn how to build muscle). It is thus only logical that the intention of Sumiaki Maeo's, Yasuhide Yoshitake's, Yohei Takai's, Tetsuo Fukunaga's and Hiroaki Kanehisa's follow up study was "to clarify neuromuscular adaptations following 12-week maximal voluntary co-contraction training" (Maeo. 2013b). In that, the researchers hypothesized that

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  the training modality with maximal voluntary co-contraction would increase both size and strength capability of the exercised muscles, and
• training unsing co-contractions does not change involuntary coactivation level during MVC of the agonist alone

In other words: The researchers wanted to make sure that (a) this form of training builds strength and muscle and (b) that it does not have lasting potentially performance decreasing effects on the co-activation of the triceps / biceps, when you actually want to use only one of them (imagine you want to curl the weight up and your triceps works against you).

The study protocol

To satisfy their research interest, the researchers from the Department of Sports and Life Scienceat the Japanese National Institute of Fitness and Sports in Kanoya recruited 16 healthy young men.

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The guys, who were in their early twenties, lean, healthy and habitually active, but not involved in regular exercise programs with a duration and frequency of more than two 30 minute exercise sessions per week, were then randomly assigned to two groups: A training group (T) with 9 participants and an inactive control group (C) with 7 participants. It goes without saying that all participants had to abstain from additional physical activity over the course of the whole study period during.

In those 12 weeks the subjects in the the subjects in T group participated in a 12-week training program with maximal voluntary co-contraction of the elbow flexors and extensors of the right arm 3 times per week.

Usually this would be the paragraph of this SuppVersity article, where I would give you a concise summary of the exercise protocol. In view of the fact that I doubt that many of you are actually familiar with muscular co-contractions, I decided to use a somewhat abridged quote of  the scientists' lengthy, but comprehensive explanation of the procedure (see red box).
Basically what the subjects were doing could be summarize as 10x4s maximal isometric muscle contractions with 4s break between each contraction for one set and 5 of these sets with an interim of 2 minutes between each of them three times per week.

Now for those surprisingly impressive results

If you do the math and add up the actual time under tension for this 12-week experimental intervention, you will get 10 × 4s isometric contractions × 5 sets × 3 / week × 12 weeks = 7200s or 2h. That's not really much considering the fact that it lead to strength and size increases of +15% / +27% and 4% / 4% in the elbow flexors (biceps) and extensors (triceps) of the previously more or less untrained, but no necessarily sedentary subjects.

Figure 1: Pre vs. post measures of muscle thickness, MVC torque and coactivation level (Maeo. 2013b)

As you can read in the small box in Figure 1 the increases in size and strength did not occur rapidly after two or three weeks and were then followed by a plateau.In fact, the researchers recorded statistically significant strength and measurable, but statistically not yet significant size gains after 4 weeks.

Probably effective for increases in dynamic performance, as well

Now, brute strength and a huge muscle mass are by no means what all athletes are striving for. For many athletes improving their dynamic performance and strength, which would have required the measurement of changes in isokinetic torques for elbow flexors and extensors in both eccentric and concentric conditions, is at least as important. It is thus more than noteworthy that data from Maoe et al.'s previous 4-week study (Maeo. 2013a),

"[...]in which untrained individuals conducted 4-week co-contraction training, showed that the co-contraction training significantly increased isokinetic torques for elbow flexors and extensors in both eccentric and concentric conditions." (Maeo. 2013b)

As the researchers rightly point out, we do thus have reason to believe that "contraction training is also effective for improving dynamic performance, at least for untrained individuals" (Maeo. 2013b). With respect to trained athletes, the reaserchers do yet argue that they'd require higher exercise intensities to achieve additional improvement in muscle strength than non-athletes (Alway. 1992; Cormie. 2011). This, as well as the emphasis sports specific training puts on ballistic, plyometric, and weightlifting exercises involving sports-specific and/or multi-joint movements (Cormie. 2011), make it difficult to believe that similar training results could be achieved by performing maximal voluntary co-contraction.
References:

• Alway, S. E., Grumbt, W. H., Stray-Gundersen, J. & Gonyea, W. J. (1992). Effects of resistance training on elbow flexors of highly competitive bodybuilders. Journal of Applied Physiology, 72(4), 1512-1521.
• Cormie, P., McGuigan, M. R., & Newton, R. U. (2011). Developing maximal neuromuscular power. Sports medicine, 41(1), 17-38.
• Maeo, S., Yoshitake, Y., Takai, Y., Fukunaga, T., & Kanehisa, H. (2013). Neuromuscular adaptations following 12-week maximal voluntary co-contraction training. European Journal of Applied Physiology, 1-11.
• Maeo, S., Yoshitake, Y., Takai, Y., Fukunaga, T., & Kanehisa, H. (2013). Effect of short-term maximal voluntary co-contraction training on neuromuscular function. International journal of sports medicine, (EFirst). 
• Tyler, A. E., & Hutton, R. S. (1986). Was Sherrington right about co-contractions?. Brain research, 370(1), 171-175.