Thursday, June 30, 2011

Food For Thought - Fasted, Low Glycogen Training And Endurance Sports

 Fasted Training

Found this posting on Martin Berkhan's Leangains website and is definitely food for thought.Results of a 2010 study by The Institute of Food Nutrition and Human Health, Massey University, Palmerston North, New Zealand.

"The main findings of the present study were that: training in an overnight-fasted state enhances storage of muscle glycogen compared to training in the fed state; skeletal muscle of men and women respond differently in terms of oxidative activity to training in the fed and overnight-fasted state; and peak VO2 and peak power improved more when training in the fasted state compared to the fed state....."

Martin provides an excellent synopsis of the study that has produced some very interesting results in terms of fasted training in regards to VO2Max, power and muscle glycogen. In a nutshell.....

VO2 Max Increase -  Fasted: +9.7% , Fed: +2.5%
Muscle Glycogen Content Increase - Fasted: +54.7% , Fed: +2.9% increase
Citrate Synthase(CS) Increase - Fasted: +17.9% ,Fed: +19.1%
3-hydroxy-coa dehydrogenase(HAD) Increase - Fasted: +3.5%,Fed: +9.1%

The increase in both VO2 Max and muscle glycogen for the fasted training group over the fed group is remarkable. Both CS and HAD are influenced by gender so once the numbers of both groups are re-examined by sex it indicated that the effects of fasted training were not all inclusive.

"Men attained a more much better response from fasted training, while women received a more favorable response from fed training."

This evidence validates earlier research on the subject......

"Two fairly recent studies has lent credence to this notion (De Bock and Nybo). While the researchers didn't find any significant differences in some of the measured variables, it's interesting to note that the fasted-trained groups in both studies showed higher levels of resting muscle glycogen concentrations after training. Similar to the anabolic rebound for fasted weight training, there seems to be an anabolic rebound during feeding after fasted endurance training through more efficient glycogen storage."

Training Low and Racing High

"The idea of training when the body is low in glycogen and then racing when glycogen stores are full is gaining popularity with endurance athletes particularly ultrarunners. The idea makes sense, training with low levels of glycogen teaches your body to burn fat more efficiently therefore preserve your very limited glycogen stores. Even a very lean athlete of 5% body fat and weighing 60kg will still have 3kg of fat which equates to 27000 calories compared with approx 2000 calories of glycogen."

The author does make an important stipulation between fasted training and low glycogen training as they are not the same thing.....

"Being in a fasted state doesn’t mean you have low glycogen levels, your muscle glycogen levels can be very high in a fasted state because if you haven’t exercised since your last meal then there is no need for the body to use any of its stored muscle glycogen. In a fasted state your blood glucose levels and liver glycogen levels will be low as this is what the brain uses for energy.... A low glycogen state means your muscles don’t have much glycogen left in them."

Low Glycogen Training

Low glycogen training also appears to offer benefits for endurance athletes.Increasing AMPK activates the buildup of mitochondria which supply most of the the energy that powers our muscles when cycling. The better the signalling function = the greater the AMPK activation = muscles accrue more mitochondria = greater capacity for producing aerobic energy.

"Training at high intensity activates AMPK at a greater rate, plus we know this effect is improved when training at lower glycogen levels, so this session gives twice the activation." - Dr Keith Baar, of Dundee University

It appears that both fasted training and low glycogen training can impart potential benefits for endurance athletes and a combination of the two may provide benefits with different gains.

"There are essentially two different types of train-low strategies. The first is to work out in the morning after an overnight fast, while also avoiding the intake of carbs as you exercise. In this situation, your muscle glycogen stores will likely be high, but liver glycogen stores will be low. The second method involves working out twice in one day and not consuming many carbs between workouts. In this scenario, the second workout is done in a muscle-glycogen-depleted state. The two approaches appear to lead to somewhat different training adaptations, so incorporating both into your workouts may have benefits".

There are some questions that need to be addressed namely the subjects of the studies. Were they already conditioned athletes or average "joes". That may have a definite impact upon some of the final performance gains.

One of the main rebutals is the question of training intensity..or lack thereof. In terms of the intensity of fasted/low glycogen training that also depends upon whether the test subjects were already conditioned to "low" training......

"Were the athletes adapted to low glycogen training? Taking athletes who are probably used to functioning on a high carb diet & then throwing them into this sort of study, you will see a drop in power unless they get a chance to adapt. I know when I shifted from a higher carb diet to a higher fat diet, my cycling went flat for 3-4 weeks. Power progressively came back after that point however." - J Scott.

From my personal experience I have not seen a noticable decrease in performance when training in a fasted state. Since my practice of low glycogen training is in it's infancy performance questions will need to be addressed at a later date. Work in progress. My approach towards fasted/low glycogen training is two fold. Both will help develop fat adaptation and metabolic flexibility and that was my original focus. If I realize better muscle glycogen recovery/storage and improved VO2max as a result that is definitely a bonus.

Interesting stuff. When you think about it the human body is an amazing machine.

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