· Index Carbohydrate Depletion - Is it for You?
	Louise Burke, Australian Institute of Sport, Canberra, Australia

The original carbohydrate loading protocol was probably one of the first modern sports nutrition strategies to receive widespread publicity. It had all the ingredients to make a good story - scientists using special techniques to study a muscle, evidence of performance improvements, and good timing. It hit exercise science journals in the early 70s, then found its way into running magazines during the start of the popular running boom. For both elite and recreational runners, this new carbohydrate loading technique seemed like a perfect prescription to build up muscle glycogen.

The depletion phase in this protocol is defined and tough - a long exercise session one week out, followed by 3-4 days of minimal carbohydrate intake and continued exercise. If anything, the rigid instructions and the challenge add a sense of mystique. It has become part of the endurance athletes folklore. So, it is both surprising and understandable that anyone would ignore the 1980s development of a "modified" carbohydrate loading technique which offers elevated muscle glycogen levels to well-trained athletes without the need for a glycogen stripping phase. But many top athletes still include a depletion.

The surprising part is that an athlete would submit to the unpleasant side effects of depleting if given a choice. Runners like Australian marathoner Steve Moneghetti who have written about the experience of a severe depletion phase describe overwhelming fatigue, irritability, reduced tolerance to anything from people to bugs to injury, and a marked reduction of performance. The body, brain and muscles are being deprived of carbohydrate fuel, and nothing functions well in the short term. For some athletes, carbohydrate restriction means substitution with a high fat and protein intake. However, even if you start that way, after a day or so most athletes will experience loss of appetite as their metabolism shifts to ketone production. Since it is both practically and physiologically difficult just to eat fat and protein, most athletes probably end up adding some carbohydrate by the end of the depletion phase, therefore not depleting properly. Athletes that do follow the protocol hope that by pulling themselves down hard, the next phase of loading will spring them back to new heights.

So why does the depletion phase persist? Some athletes are old-fashioned and stick to what previous legendary athletes and coaches did. Perhaps they just read old magazines and studies. Certainly the ritual of a special practice is hard to break away from - especially if you are the kind of athlete that believes in "no pain, no gain", or that greater effort will bring greater rewards. Many athletes are guided by superstition as much as experience. If an early competition success, or the success of a rival involved a depletion preparation, the athlete may want to follow what seemed to work. In a sport like marathon running, athletes may only compete at their highest level a couple of times each year. Therefore it is difficult to experiment with and assess the contribution of many different variables that affect the final result. Athletes who dare to try the new modified approach may have a bad race for an unrelated reason but may blame their new loading approach. And of course, some athletes may say that they deplete, without really doing it rigorously.

So should we just forget about about depleting? Well, maybe it works! Maybe it does increase the subsequent muscle loading. Maybe it offers the athlete some metabolic improvements by serving as a shortened version of the fat adaptation technique that is currently under trial. Scientists may need to re-open the files on the metabolic, glycogen storage and performance outcomes following a depleted and non-depleted loading before we can put this issue to its final rest.

In the meantime, athletes will continue to do what they think works best for them. Some endurance athletes aren't able to consider a depletion/loading protocol due to practical restraints. Athletes who compete frequently such as those in weekly sports competitions, or those undertaking stage or tournament events, simply do not have the time to undertake a long preparation between their events. Others will find that the downside of depletion is not worth the risk, or that any small merits are overshadowed by the depletion protocol.