HIT Your Satellite Cells to Increase Your Gains! Only High Intensity "Cardio" Exercise Will Fuel Your Satellite Cell Pool and Set You Up For Future Muscle Growth.

Image 1: NO-mediated satellite cell
recruitement (Anderson. 2000)

You have read it on the SuppVersity, you have heard about it on Carl Lanore's Super Human Radio and the BodyRX Show and those of you who have seen videos or pictures from the latest New York City Marathon, should actually have been able to infer it from the way the "finishers" looked like. Intensity not duration is what counts, when doing "cardio". Yet, as a very recent (7 days old) study shows (Naito. 2011), High Intensity Training (HIT) will not only burn off your lovehandles, while keeping your muscles intact, it will also prime your musclefibers for future growth by increasing the number of satellite cells, the small dormant mononuclear progenitor cells that are sandwiched between the basement membrane and sarcolemma of the fibers of your muscle and are recruited, whenever your body feels that you could use a little more or have to replace some damaged muscle mass.

While I will go into more detail on how your muscles actually grow in the upcoming parts of the Intermittent Fasting Series, in the course of which I am going to explain how you should train, eat and sleep in order to exploit all three major pathways of skeletal muscle growth, I want to give you a sneak peak at what you are going to learn, by highlighting that protein synthesis, i.e. the accrual of muscle protein in existing myonuclear domains, and the recruitment of satellite cells to replace damaged or add new myonuclei are distinct processes. It should nevertheless be obvious that with all the protein synthesis of the world you will - sooner or later - hit a plateau, when all the existing myonuclei have "blown up" to their maximal size - or as Naito et al. put it: "Increases in the number of satellite cells are necessary for full skeletal muscle growth and hypertrophy" So, whenever the existing myonuclei have reached their "full potential", the only way to keep growing is by adding new myonuclei via satellite cell recruitment. Keep that in mind before you discard the results the following study, because the "HIT rats" did not gain more "active" muscle than the "LIT rats" ;-)

In their experiment Hasashi Naito and his colleagues from the Tokai University and the Juntendo University in Japan put 17-week old (these are old rats!) female Sprague-Dawley rats on one out of four exercise regimen (for a detailed outline of the regimen, cf. table 1):

1. High Intensity, High Duration (90H)
2. High Intensity, Low Duration (30H)
3. Low Intensity, High Duration (90L)
4. Low Intensity, Low Duration (30L)

Table 1: Outline of the exercise
protocol (from Naito. 2011)

In the course of the 10-week study period the rats were exercised five times a week on one of those funky rodent treadmills. What's funny is that despite the fact that, as the scientists say, "[e]lectrical shocks were used sparingly to motivate the animals to run", two of the critters in the high intensity groups refused to do their workouts, which reminds me of what Dr. Layne Norton had to say on one of the past installments of BodyRX Radio: "Most of those who will tell you that they cannot do HIT for whatever reasons are usually just too lazy" - we may thus consider those two lazy rats as evidence for the accuracy of the model... and by the way, it did not save them from being anesthetized and deprived of their plantaris muscle, which was weighed and analyzed for its fiber composition and satellite cell count.

As it was to be expected in view of the high age of the rats, where skeletal muscle mass maintenance, may be considered a success, there were no statistically significant increases in plantaris and/or body mass in any of the treatment groups.

Figure 1: Changes (compared to untrained control) in number of myonuclei and satellite cells per muscle fiber (data calculate base on Naito. 2011)

Despite the absence of measurable skeletal muscle hypertrophy, the pronounced (cf. figure 1) and fiber-type specific (cf. figure 2) increases in satellite cell counts in the high intensity groups may well be considered as the necessary prestage of a hypertophic growth spurt, which could be triggered by appropriate training (which would obviously be strength training) and endocrine (more on that in the conclusion) stimuli.

Figure 1: Satellite cells per muscle fiber in type I (slow twitch) and type II (fast twitch) muscle fibers of rats in the control and the high intensity, high duration (90H) groups (data calculate base on Naito. 2011)

In that, it is also interesting to note that contrary to popular believe, the slow-twitch type I fibers, with their greater number of satellite cells, have an increased propensity for maximal myonuclear numbers, the fable of the "hypertrophy-prone fast-twitch type II" fibers, on the other end, is a consequence of their ability to accumulate more protein per myonucleus. And while I will - as promised in the red box above - dig deeper into that in future installments of Sunday's Intermittent Thoughts, I can already tell you that the fiber composition (not the size!) of professional body builders is almost identical to those of non-strength-trained individuals and thusly fundamentally different from that of strength athletes, like powerlifters (Tesch. 1982) - in order to achieve maximal muscularity you can thusly not neglect your type I fibers!

That being said, both the strength training, which would make use of the increased propensity to grow by recruiting satellite cells to form new myonuclei, as well as the necessary local IGF and MGF responses, which have been shown to decrease with age (Grounds. 2002), were absent in the study at hand. In someone like you, a young, vigorous strength trainee, both stimuli will yet obviously be present in abundance (at least I would hope so ;-). Accordingly, 1-3 high intensity (and in view of the fact that the duration, 30 vs. 90min, did not make a difference probably also high intensity interval) training (HIT or HIIT) sessions per week could not only make your increasingly fat-free muscles shine in their full glory, they will also "precondition" you for future muscle growth by increasing your satellite cell pool. I would thus suggest, you better not join the two lazy rats from the study, and rather find yourself the next best track to do a bunch of sprints ;-)