|No matter how close we look, the influence of previous, i.e. GH, IGF-1 and testosterone, as well as novel, i.e. IL-6 and AR expression, potentially growth promoting suspects remains elusive.|
The results the scientists from the McMaster University probably won't add much to our understanding of the systemic effects of IL-6 and other myokines. What certainly do, though, is to support the notion that "inflammation" can have profound and very far-reaching effects on our physiology (learn more).
Does IL-6 build muscle?
The mere idea that IL-6, a molecule of which most people think that it was a good measure of how messed up your health actually is, could be a promoter, or at least a measure, of skeletal muscle growth in response to a workout sounds about as logical (or illogical, if you will) as the previously established fact that the allegedly anabolic hormones testosterone, IGF-1 and growth hormone don't show the slightest correlation with the exercise induced skeletal muscle growth (West. 2011; learn more in "Anabolic Workouts Revisited").
|Figure 1: Relative increase in muscle CSA change for androgen receptor density and p70S6K expression (left) and individual correlation of endocrine changes and muscle CSA (right), data based on Mitchel. 2013)|
Strength training can increase the androgen receptor density
Less well-known, but also not really new is another observation Mitchel et al. made: The resistance training lead to an allegedly subject specific and overall insignificant increase in the density (number per area unit) of androgen receptors; and though the overall increase may not have been statistical significant, the correlation of the the increase in androgen receptor density and the lean muscle gains of the subjects was.
|New myonuclei (blue) are necessary to keep growing (learn more)|
"Our study corroborates previous findings that mean AR protein expression was not increased following resistance training; however, the response had marked heterogeneity, with some subjects showing a marked (1.5 - 2.5 fold) increase in AR protein content [...] Despite no statistically significant change in AR receptor protein content, there was a correlation between AR protein content with fibre hypertrophy. Our results suggest that changes in AR content may be part of a muscle-specific response present to a greater degree in responders and responsible for some (~25%) of the variation in muscle fibre hypertrophy." (Mitchel. 2013)With regard to the correlation (I want to emphasis that we don't have enough evidence to do anything, but speculate about causative effects, here), it may be worth mentioning that the statistical significant association between androgen receptor density and the changes in muscle cross-sectional area was more pronounced in the "strength type" fast twitch (type II) than in the "endurance type" slow twich muscle fibers (0.6, p = 0.002 vs. 0.47, p= 0.023).
For IL-6, on the other hand, it was the exact opposite. Unlike the number of androgen receptors per muscle area, the amount of interleukin 6 that was released or, as Mitchel et al. say, "filtered" from the muscle into the blood stream in response to the workout exerted a minimally more pronounced effect on the slow twitch "endurance type" fibers (type II).
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- McKay BR, De Lisio M, Johnston AP, O'Reilly CE, Phillips SM, Tarnopolsky MA, Parise G. Association of interleukin-6 signalling with the muscle stem cell response following muscle-lengthening contractions in humans. PLoS One. 2009 Jun 24;4(6):e6027.
- Mitchell CJ, Churchward-Venne TA, Bellamy L, Parise G, Baker SK, et al. Muscular and Systemic Correlates of Resistance TrainingInduced Muscle Hypertrophy. PLoS ONE. 2013; 8(10): e78636
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