Nonuniform Muscle Hypertrophy: Activation Patterns and Eventually Exercise Selection Determine Triceps Growth

Is it possible that you can - within your genetic limits - influence the growth pattern of your tris by the way you train?

"Localized muscle growth? Wtf now you're kiddin' me, right!?"Well, I want to be honest with you. It's not like you could actually grow exclusively the peak of your biceps, but the fact that even the observation that the maximal increase in muscle cross-sectional area does actually correspond to the area of maximal stimulation can be considered a "novel finding", is testimony to how under-researched the optimal modalities of training for such profane things as cosmetic muscle gains actually are. In the end, you'd even have to wonder that Taku Wakahara and his colleagues from the Waseda and Doshisha and Ritsumeikan Universities in Japan even dared investing precious time and money into a part of human physiology that's still looked down upon by large parts of the scientific establishment.

Maybe, it's like a carte blanche young researchers have!? After all, the study was supported partially by a grant for young scientists. So, before we get to the details, let's briefly thank the board members for turning a blind eye to the fact that the purpose of the present study was ...

"[...] to examine whether the regional difference in muscle hypertrophy induced by a training intervention corresponds to the regional difference in muscle activation in the training session." (Wakahara. 2012)

... and did not involve the frail, the obese or the frail and obese, but 24 completely healthy young male volunteers. With an average age of 26 years and 66kg on a 172cm frame (likewise averages) the letter were yet either sedentary or (maximally) "recreationally active" and had not been involved in a regular resistance training program for the upper limbs for six months before the beginning of the experiment.

Why would they use sedentary / hardly trained subjects?

Now you may certainly argue that it would be nice to see the very same study done in young bodybuilders. And this would in fact have been quite "nice" it would probably have been quite useless, as well. After all, you would have been hard pressed to measure any significant significant differences in muscle growth in already highly trained subjects.

That being said, there is still something to criticize: Why on earth do you need N = 12 subjects in the sedentary control group? I mean, it's not exactly likely that people who are sitting around anyway are suddenly growing big guns due to anything, but the 12-week exercise intervention they were part of? If the 12 subjects in the ...

• The lying dumbbell press was performed with a TUT of 2s on the concentric and 2s on the eccentric potion of the exercise.

  control group, who did not perform resistance training, but maintained  their  normal  activities  during  the period,

had, for example, performed the same workout as the ...

• training group, who performed 5x sets of 8x reps at 80% of their pre-determined 1-RM max of a dumbbell press-type movement; a multi-joint exercise that involved forearm extension and arm flexion in the sagittal plane to failure (if necessary the instructors helped them to complete any missing reps; rest between sets was 90s),

but with different rest times or using different exercises the scientists would have been able to collect much more valuable data in the same 12-week study period. Information muscle-heads like you and me would have highly appreciated.

But again, who am I to pass criticism on Taku Wakahara, Atsuki Fukutani, Yasuo Kawakami, and Toshimasa Yanai? A smartass blogger... no, I suggest we'd better be happy with the results and accept the limitations of the study at hand.

So what were the results, then?.

Before the training intervention, there was no significant difference in the age, body height, body mass or the maximal CSA of the triceps brachii between the two groups. After 12 weeks with three training sessions per week, however, the scientists did observe a highly significant increase in muscle CSA in the participants in the active arm of the study.

Figure 1: Activation patterns for lateral, medial and long head at at different distances (in cm) from the elbow joint and correspoding changes in muscle CSA after the 12 week intervention (left; figures indicate sign. diff. to position in cm); MR images used for the assessment of the activation pattern after the first session (right; Wakahara. 2013)

As mentioned before, this observation is neither surprising nor novel. What's quite telling and of practical relevance, however, is the observation that the different activation patterns the scientists had observed during the first training session, where the "%activated area of the triceps brachii had been significantly higher in the middle regions than that in the most proximal region" (Wakahura. 2013) did - just like "broscience" would have it - yield corresponding increases in the cross-sectional area in the respective parts of the muscle.

"The relative changes in CSA after the training intervention distributed nonuniformly (P= 0.029, partial η² = 0.327) along its length in the training group. The relative changes in CSA were significantly greater at 10 cm (P= 0.030, r = 0.753), 16 cm (P= 0.019, r = 0.774) and 22 cm (P= 0.001, r = 0.869) from the elbow joint that [sic!] the value at 28 cm from the elbow joint."  (Wakahura. 2013)

Interestingly, the scientists did not observe any significant change in the muscle thickness of the long head in the training group (before: 2.0 ± 0.3 cm, after: 2.1 ± 0.2 cm). This is a result that stands in line with the activation patterns Boeckh-Behrens & Buskies observed in their Y2k study on which the data in the SuppVersity EMG Series is based on (click on the respective body part below to see the activation patterns for different exercises for all muscle groups).

Chest	Biceps	Back	Core	Legs	Triceps	Shoulders
Navigate the SuppVersity EMG Series - Click on the desired body part to see the optimal exercises.

According to the said EMG data, the optimal exercise for the caput longum are dumbbell triceps kickbacks on an incline bench - an exercise that was obviously not part of the workout. The same goes for possible replacements, such as the seated dumbbell extension.

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Suggested read: "Shoulder Presses Ain't for Delts Only! Standing, Seated w/ BB or DB, They Also Hammer the Core, Biceps & Triceps"(read more)

Practical implications: Irrespective of the previously discussed limitations / shortcomings of the study at hand the results are anything but worthless. After all the correspondence of the activation patterns and hypertrophy response the scientists observed in the study at hand supports the notion(*) that EMG activity patterns as they were measured by Boeckh-Behrens & Buskies (see The SuppVersity EMG Series) are practically relevant and can be used as a starting point to build highly specific hypertrophy workouts.

In this context, the "(*)" after the expression "supports the notion" is of utmost importance. Why? Well, the study at hand used MR imaging, not electromyography (EMG), to evaluate the skeletal muscle activation patterns and - probably even more importantly - a sluggishly performed DB kickback is not going to yield the exact same activation patterns as a picture perfect DB kickback "right from the textbook".

With form, inter-individual physiological difference (e.g. the length of your limbs), personal preference, training experience, auxiliary movements etc. all having a more or less pronounced influence on the activation pattern, EMG studies or other data on activity patterns should always be regarded as a guide, as inspiration to give things a try - not as a prescription! In the end, it will always be up to you or an experienced trainer who is actually watching you as you train (!) to pick the "truly optimal" exercises for you, as an individual.

References:

• Wakahara T, Miyamoto N, Sugisaki N, Murata K, Kanehisa H, Kawakami Y, Fukunaga T, Yanai T. Association between regional differences in muscle activation in one session of resistance exercise and in muscle hypertrophy after resistance training. Eur J Appl Physiol. 2012 Apr;112(4):1569-76.
• Wakahara T, Fukutani A, Kawakami Y, Yanai T. Nonuniform Muscle Hypertrophy: Its Relation to Muscle Activation in Training Session. Med Sci Sports Exerc. 2013 May 7.