Monday, April 2, 2012

45x More Testosterone Yet Identical Increase in Protein Synthesis: MPS Response to Exercise + 25g Whey in Men vs. Women Challenges Common Wisdom About Androgens

Image 1: Is it not testosterone that makes the difference?
It is an open secret that women are having a much harder time building muscle than men, and it is another instance of (bro-)scientific wisdom that the obvious lack of testosterone in female strength athletes would be the underlying reason. Right from Stuart M. Phillips lab at the Department of Kinesiology of the McMaster University in Hamilton, Ontario, Canada, comes a new study (West. 2012) which puts yet another questionmark behind the anabolic prowess of testosterone (if you still believe that a transient increase in testosterone will help you build muscle, I suggest you read up on "The Big T" in the Intermittent Thoughts on Building Muscle).

Women are different, but it's not about protein synthesis

In the recently conducted trial Daniel W.D. West, who has also been the lead author of the "Never Sip Your Whey" study, I covered back in November 2011, undertook another attempt to identify the intricate endo- and paracrine mechanisms of skeletal muscle hypertrophy and its sex-specific variability. To this ends, West et al. recruited 5 male and 5 female subjects, who "who were habitually engaging in two to five sessions of physical activity per week including", yet did not train legs more than twice a week.
Image 1: In this case, testosterone took a backseat, as well. With synthol, protein synthesis is yet unnecessary anyway.
Note: The selection of advanced trainees as study participants is the first huge plus of this study. After all, we all know that the exercise induced hypertrophy response diminishes with training and those of you who read the whole Intermittent Thoughts on Building Muscle series will also be aware that the protein synthetic response is limited by the maximal domain size. Further growth thusly requires restructuring / the recruitment of satellite cells and installment of new myonuclei (cf. "Growing Beyond Temporary Physiological Limits"), a time-consuming and complex process which is probably one of the underlying reason for the "growth difference" between beginners and advanced strength athletes.
On the day of the experiment, the study participants, who had consumed a standardized diet containing 15% fat, 30% protein and 55% carbohydrates (the macronutrient ratio was adapted to their habitual diets) on the previous day, reported to the lab at 6am. After the infusion of the tracer that is necessary to evaluate the protein flux and an initial biopsy, all subjects performed a bout of  intense, high-volume lower body exercise consisting of
  • 5 sets of 10 repetitions of leg press at ~90% of their individual 10RM, and
  • 3 super-sets of 12 repetitions of leg extension/leg curl at ~90% of 12 RM
The rest intervals between the sets were 60s, so that the whole workout should not have lasted longer than max. 20min. Directly thereafter, the subjects consumed the "obligatory" (for Phillips lab this has in fact become obligatory ;-) 25g of whey protein from the usual New Zelandian source, Phillips et al. used in all their previous study (as ridiculous as this may sound but this is a nice means of standardization ;-) and rested in a supine position for the rest of the trial. Biopsies were taken and the subjects who were sent home with a launch packet consisting of their standardized meals had to report back to the lab on the following morning for another three biopsies 24h, 26h and 28h after the test workout (the subjects remained fasted and received another 25g of whey 26h post, i.e. before the last four blood samples were drawn and the last biopsy at 28h post was performed).
Figure 1: Serum testosterone levels (in nM) and myofibrillar fractional protein synthesis rate (in %/h) before and after the resistance workout, as well as on the morning and at noon of the 2nd day (data adapted from West. 2012)
As the data in figure 1 shows, the (expected) huge difference in both basal as well as exercise induced increases in circulating androgen levels (45-fold in men vs. women) had no (not even a statistically non-significant) beneficial impact on the exercise induced increase in protein synthesis in the 28h window of opportunity (cf. "Opening the 'Anabolic Barn Door' with the Key of Science").
Akt Ser473 phosphorylation increased at 1h ( P < 0.001, main effect for time) and to a greater extent in men (sex × time interaction, P = 0.018). Phosphorylation of mTOR Ser2448 was increased at 1, 3 and 5 h (P < 0.001; Figure 4B); there was a main effect for sex (men > women, P = 0.003). Phosphorylation of mTOR Ser2448 was elevated similarly between sexes after next-day protein feeding, approximately 26 h after the exercise bout (sex  × time interaction,  P = 0.49; main effect for time, 28 > 26 h,  P = 0.006).  Phosphorylation of p70S6K1 Thr389 increased at 1, 3 and 5 h (all  P < 0.001; sex × tim e interaction,  P = 0.13) and there was a significant interaction with next-day feeding (28 > 26 h in women only, sex × time interaction,  P = 0.016; data not shown). Androgen receptor content was greater overall in men (P = 0.049) but there was no significant interaction ( P = 0.47).  
The greater increase in mTOR and Akt (both hitherto regarded as the "gas pedals" of the skeletal muscle protein synthetic machinery) are not only less pronounced, than one would expect if there was a direct interaction with testosterone levels, they also lack real world significance. After all, the area under the myofibrillar protein synthesis curve (a measure for the total protein synthetic response to exercise) was identical in the 1-5h period right after the exercise and - although West et al. did not include the respective data in their article - I would suspect that the data from the subsequent day (cf. figure 1, right) would even suggest that it must have been slightly greater in the female participants.

Testosterone useless and mTOR and Akt unreliable indicators at best?

Now, which conclusions shall be drawn from these results? Is testosterone useless? Does it not contribute to the overall greater muscle mass in men compared to women? It stands to reason that this conclusion would be about as flawed as the notion that testosterone alone would suffice to build muscle. Rather than its "inefficiency" in building muscle, this study only shows that its importance in relation to the exercise-induced increase in protein synthesis is probably way overrated.

A similar point could be made for mTOR and Akt, as well, though. Or as West et al. put it in their discussion of the results and the respective implications for future studies:
In light of this disconnect, it is worth recognizing that the phosphorylation of signalling proteins is a temporal snapshot of the propagated signal for translation initiation. It is also unclear if there is a minimum threshold signal required to initiate and completely activate or  ‘turn on’ translation. If  there is such a threshold then it seems plausible that greater phosphorylation above such a  threshold would be unlikely to further amplify the signal/lead to increased rates of translation.
For a physicist or anybody who knows a thing about "energy levels" the existence of "threshold" levels in processes taking place at a molecular level should not come as a surprise.

I suspect, we are still missing the boat with our focus on protein synthesis alone

Another question, I have been hinting at in many of my previous blogposts on the insightful studies from Stuart Phillips lab at the McMaster University, is yet whether or not the acute increase in protein synthesis (alone) is actually an acceptable predictor of skeletal muscle hypertrophy, a process which, as I have explained in detail in the Intermittent Thoughts on Building Muscle is only partly mediated by the simple accrual of amino acid chains (=proteins) within existing myofibrillar domains.
Figure 2: Graphical illustration of the processes and their respective triggers which contribute to the exercise induced increase in skeletal muscle mass (click here for detailed elaborations).
If you take another look at the complex network of endo- and paracrine signalling cascades and the number of factors which contribute to a process that is generally reffered to as "skeletal muscle hypertrophy" (cf. figure 2) and is, at least in my mind, falsely reduced to the influx of amino acids into the muscle, it should be clear that testosterone does play a central role in the actual exercise induced growth response. That the latter is less pronounced than bro-science would have it (esp. when we are talking about physiological levels, cf. "Quantifying the Big T") and that testosterone itself and its metabolites, DHT and estrogen are probably of greater importance in the "restructuring" process, which in turn facilitate the accrual of even more protein within the muscle, does after all not imply that the huge differences in androgen levels are not the reason for the differential hypertrophy response in men and women - and I guess, I don't have to tell you that you just have to take a glimpse at the female IFBB (International Federation of Bodybuilding and Fitness) competitors to know that androgens can make a difference ;-)