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Old 11-30-2008, 04:43 PM
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Cell signaling in response to endurance exercise

Endurance exercise activates a negative regulator of contractile protein synthesis. This is known as AMP activated protein kinase. What is interesting though is that this kinase actually stimulates mitochondrial biogenesis or production. Thus, endurance exercise provides a mechanism via AMPK whereby it can suppress increases in muscle growth, while simotaneously increasing aerobic capacity( mitochondria).
We as bodybuilders simply need to understand the implications of this. Clearly aerobic exercise can mediate fat loss via increased mitochondrial density, but by activating AMPK it attenuates gains in the gym in musculature. I am researching this subject now and will be writing on it in JHR in the up and coming year.

Feeding and cell signaling
Wont go into to much detail here, but it essentially points out the fact that both insulin and amino acids activate protein synthesis through mTOR, but through different mediators, thus in order to maximize protein synthesis you need an optimal combination of carbs and amino acids.
I would also add that this differs from resistance and cardio. With cardio for example protein synthesis is turned off or lowered via AMPK. In this instance extracellular Leucine levels become that much more critical to try and at least counter the effects of cardio, because cardio also depletes extracellular Leucine levels.

Sex differences

In a fasted state – No appreciable differences exist
During cardio – women rely less on protein for substate then men, so it may not be as catabolic for them
Resistance exercise – not a lot of data on acute changes in protein balance to resistance exercise.
Let me add my insights here though. The professor I work with, Dr. Jeong-su Kim has done extensive work on both genetic and gender differences between individuals. Chronic resistance training studies clearly demonstrate that women demonstrate less hypertrophy then men. Why is this the case?

1. Muscle growth is a factor of two elements. The first is an expansion of the muscle cell without the addition of new nuclei. This process is probably similar between men and women
2. After you grow to a certain point you cannot grow any further without activating satellite cells and adding new nuclei to support further protein synthesis. This is what lacks in capacity in females relative to males and explains differences in growth, and is probably mediated by greater anabolic hormone and local growth factor environment in men than women

Overall shortcomings In the literature – changes in protein breakdown following exercise. But Gabe andLayne will tackle this!
Dr. Jacob Wilson, Ph.D, CSCS
Professor of Exercise Science, University of Tampa Bay

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