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As explained previously in this column, cells respond to local signals and put in motion a series of events to adjust to the changing environment to minimize disruption to the normal state (homeostasis).  If a cell is energetically challenged, it makes changes so that the cell maintains an adequate energy supply for what it needs to accomplish.  Endurance exercise, such as cycling, is highly dependent on these adaptations since they are to a large degree what improve endurance performance.  One of the main energetic signals is glycogen storage.  As you may recall, glycogen is the storage form of glucose and it is limited (as opposed to fat) in its storage capacities.  If glycogen is depleted, the signal to the cell is that glucose stores are depleted and thus the cell has to become more efficient in energy storage or energy usage.  A series of recent experiments have tried to take advantage of this phenomenon by having athletes purposely train in the glycogen-depleted state in order to trigger exaggerated endurance training responses.  This concept has been termed “train low”.


There are a couple of things about train low that should immediately jump out at you.  First, it is counter to the notion of carbohydrate repletion during and after exercise since in the case of train low you are doing exactly the opposite.  Second, those that have faced a bonk before realize how difficult this type of training is.  The initial study that precipitated the protocol was one done in a well controlled, but somewhat contrivedfor the sake of control, experimental design.  Subjects performed a one-legged exercise training protocol of kicking against a flywheel.  In one leg, a prolonged submaximal bout of exercise was performed once per day.  In the other leg, a bout of exercise was performed in the morning, no carbohydrate was provided in order to keep the leg glycogen depleted, and a second bout was performed later in the day.  The leg that did two exercise bouts had the next day off so that by the end of two days, both legs had done the same amount of work.  Again, the difference is that one leg did all of its bouts glycogen replete and the other did half of its bouts glycogen depleted.  The outcomes of this study showed that indeed, the cell triggered some responses indicative of an extra training effect in that leg that did half of its bouts of exercise in the glycogen depleted state.  Since this initial study, other studies have reproduced this trial in a more realistic manner that used cycling training and subjects that were good endurance athletes.  

As many of you know, high intensity training is a necessary component of your race training.  You may also know that it is very difficult to perform high intensity exercise in the glycogen-depleted state.  Therefore, there has been a couple of modifications to the train low protocol to fit strategies of the real athlete.  One such modification is to perform a high-intensity exercise bout in the evening, go to bed without glycogen repletion, wake up and perform a low-intensity bout of exercise still in the glycogen depleted state, and then eat to replete glycogen.  I think this is a very cool design to try to take advantage of these proposed adaptations.  However, despite these various modifications of the initial protocol, although studies have shown that exercise in the glycogen depleted state triggers “signals” of enhanced adaptation, there has actually been very little demonstration of performance benefits.  

Many have scratched their heads over why there is relatively little documentation of performance benefits from these approaches.  Some speculate that the since races are won by such little differences (Team Sky’s marginal gains approach) that traditional testing techniques in the lab are not capable of detecting these small benefits.  I actually think there is another reason that has to do with cellular energetics that is beyond the scope of this column.  The last very plausible explanation is that the busy recreational athlete may be doing this unconsciously in their everyday life.  How often have you trained in the morning before having breakfast, or gotten home from Wednesday Worlds and gone to bed without eating, etc. It is quite possible that undertaking some bouts of exercise in the glycogen depleted state is just the norm.   

At this point, undertaking some of your training rides in the glycogen-depleted state has the potential to improve performance.  However, at this point I believe it is just a potential.  If you believe it could have potential I see no harm in using this strategy once in a while as long as you are not doing too many (chronic glycogen depletion can lead to overtraining syndrome).  I applaud those that are thinking outside the box to come up with these novel strategies.  However, it yet remains to be seen whether these strategies are effective for elite or recreational endurance athletes.   


Additional reading:

Hansen,A.K., C.P. Fischer, P. Plomgaard, J.L. Andersen,B. Saltin, and B.K. Pedersen (2005). Skeletal muscle adaptation: training twice every second day vs. training once daily. J. Appl. Physiol. 98:93-99.


Yeo, W.K., C.D. Paton, A.P. Garnham, L.M. Burke, A.L. Carey, and J.A.  Hawley. (2008). Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens. J. Appl. Physiol. 105:1462-1470.