On Tuesday of last week I ran a research review on Casein Hydrolysate and Anabolic Hormones and Growth looking at two papers, one of which was a paper showing that the acute hormonal response (in terms of testosterone and growth hormone) to weight training had zero impact on growth. In the comments section, at least three different people asked a semi-related question that I’ve reproduced below and which I want to address in some detail today.
Question: A common recommendation bandied about by trainers is to place any LISS cardio after “lactate training” or whatever they choose to call higher intensity work, and they say that if fat loss is the aim, this will milk every last bit of effectiveness out of the low intensity work (versus keeping it a separate session entirely). And they usually say that increased lactate leads to increased GH, leads to increased lipolysis, so that when the low intensity work comes after the much higher intensity work, you oxidize more of the fat they claim gets mobilized. So does this pairing of LISS cardio after high(er)-intensity work still make it at least somewhat more effective (from a fat-loss standpoint) than when performed separately? And if so, is it more due to other things you mentioned (glycogen depletion, effect of the catecholamines, etc.), so that the intended effect is the same, it was just the purported reason for the effect that most of these trainers had wrong (namely implicating a GH-induced increase in lipolysis as the reason)?
Answer: There’s no doubt that growth hormone (GH) is involved in lipolysis although, compared to hormones such as insulin and the catecholamines (epinephrine/norepinephrine aka adrenaline/noradrenaline) it plays a distinctly secondary role. There are other hormones of course, testosterone, estrogen, progesterone, Interleukin-6 and a new player called atrial-natriurietic peptide (ANP) all play a role as well. Here I’m only going to talk about GH.
First let me define a single term which is lipolysis. This refers to the breakdown of stored fat (technically: triglycerides) in fat cells for release into the bloodstream. While there are more steps involved in losing fat (and the specific pathways are all discussed in some detail in The Stubborn Fat Solution), clearly if you can’t get the fat out of the cell in the first place, little else matters. Lipolysis simply refers to that process, whereby fatty acids stored within fat cells are broken down to be released into the bloodstream, hopefully to be burned elsewhere in the body (generally skeletal muscle or liver).
For example, while studies of injectable GH have generally crapped out in terms of muscle growth (there is an increase in lean body mass but it’s primarily water and connective tissue, not actual muscle mass), it has shown impact on fat loss. As well, the nighttime GH pulse has been shown to be important for lipolysis the next day. Finally, during periods of fasting or even low-carbohydrate diets, studies clearly show that blocking the normal GH response not only limits lipolysis, but this ends up increasing muscle loss (because the body doesn’t have fatty acids to burn).
So far so good right?
Add to that a host of studies done primarily during in the 80’s by William Kraemer and his group showing that certain training protocols (notably higher reps and short rest periods; 3X10 with 1′ rest was typically used) elevate GH and you can see where folks got the idea that training in this fashion would be good for fat loss.
I think the first place I saw this idea floated was Charles Poliquin’s original German Body Composition Training. Claimed to be based on German research into the hormonal response to training, it was based arund multiple sets of high reps with short-rest, the premise of which being to raise GH (and lactate production during training seemed to be involved somehow) to increase fat loss.
More specifically to today’s question, many trainers will use that type of training (using various permutations of Metabolic Training, discussed in some detail in Weight Training for Fat Loss Part 1 and Weight Training for Fat Loss part 2) to be followed up by low-intensity cardio. The idea being that the GH response will promote lipolysis and the low-intensity cardio will then ‘burn off the fatty acids’.
And here’s we run into the problem with the idea: the time course. Because while GH is certainly involved in lipolysis, it’s effects are pretty slow to occur. Cutting ot the chase, after a big GH pulse, you don’t really see a big increase in lipolysis or blood fatty acids until about the 2 hour mark. Which means that a protocol based around the idea of elevating GH during the intense portion so that cardio done a few minutes after will burn off the fatty acids mobilized by the GH pulse is fundamentally incorrect from a physiological point of view.
But that doesn’t mean it doesn’t work. Quite in fact, the premise is still fairly sound, this is just a place where I’m being picky about the mechanism. As discussed in Weight Training for Fat Loss Part 1 this type of training still has metabolic effects that can be conducive to fat loss (even acutely), they simply aren’t related to the GH pulse in any form or fashion.
Rather, increases in epinephrine/norepinhrine will have a much stronger acute effect on fat mobilization, and the glycogen depletion due to this type of training tends to enhance fat oxidation in skeletal muscle. Quite in fact, the two advanced protocols in my Stubborn Fat Solution are at least superficially similar to this type of training, high-intensity work followed by low-intensity work. But GH isn’t the mechanism behind it.
So bascially, what the person asking the question wrote in the second-half of his question. The combination of high-intensity followed by low-intensity work can still be effective for fat loss, it’s simply not for the mechanism stated. The impact of GH on fat loss is simply too slow to be involved. Rather, other mechanisms related to hormonal response, glycogen depletion, etc. are what are involved and responsible. GH simply isn’t relevant to the process in that short of a term.