Bonk Training

On June 8,2006 Matt Fitzgerald published, “Should you bonk on purpose?” on Active.com. CTS received a number of questions concerning this publication. Fitzgerald sites “Signaling the muscles to adapt: Train low, compete high” Bente Pedersen’s presentation at the American College of Sports Medicine conference as the science behind his “bonk training.” Pedersen however, never does discuss “bonking” per se; rather, her focus is on muscle adaptation to exercise performed twice daily versus exercise performed once daily. Exercising in a glycogen depleted state is not the same thing as “bonk training,” something Fitzgerald overlooks.
University of Copenhagen scientist, Pedersen, discussed the merits of pushing the body beyond its limits by performing twice daily exercise bouts in order to improve the training effects. She reports on her most recent study in which she compared individuals who performed exercise twice daily every other day to a control group who exercised once everyday. The groups were controlled for time, meaning both groups performed the same amount of work over the length of the experiment- albeit dolled out differently. The group that exercised twice daily exercised with depleted glycogen stores in active muscle groups. Training with depleted glycogen stores increased adaptation effects compared to training bouts following replete glycogen stores. Training in this depleted state increases the release of interleukin-6 (IL-6), a cytokine secreted by T-Cells and a myokine released by contracting muscles.
IL-6 is associated with the immune response to burns, illness, injury and fevers. In addition Fitzgerald, a columnist and not a scientist claims that “IL-6 is believed to facilitate many of the body’s adaptations to exercise training, ranging from increased fat burning to greater resistance to muscle damage.” Fitzgerald does not site his sources and I was unable to confirm each one of his claims. Increased IL-6 levels are found increased in post marathon runners (Pedersen et al), weight lifters performing eccentric contractions (Bruunsgaard et al) and hypoxic individuals (Klausen et al). IL-6 is associated with exercise and muscle breakdown, but greater resistance to muscle damage and improved cognitive function is yet unsubstantiated.
IL-6 specifically “stimulates hepatic glucose output if blood glucose concentrations fall during exercise” (Robson 2003).

Enhancing fatty acid metabolism (fat oxidation) makes athletes more efficient aerobic machines, thus able to go longer and harder, a positive training effect.
Robson’s research, a biologist from South Africa hypothesizes that after one bout of hypoglycemia (bonking experience) a subsequent exposure of hypoglycemia will elicit an increased release of IL-6, thus increasing the rate of fatty acid break down and mimicking liver glycogen as a fuel source. This would theoretically produce a heightened training effect so that athletes can come back stronger, be more efficient fuel burners and prolong their time to exhaustion.
“Bonk Training” is actually a misnomer because Pedersen does not advocate the reduction of glucose in training, but rather performing exercise bouts with a depleted state of muscle glycogen. While, Pedersen has found that glucose and anti-oxidants prevent the release of IL-6, mitigating the positive lipolytic adaptation, muscle glycogen is not the same thing as glucose. Ingesting glucose does not translate immediately to muscle glycogen. While studies have shown that glucose ingestion does spare muscle glycogen, Pedersen is careful to clarify that her study examines the result of muscle glycogen depletion on adaptation and not the restriction of glucose on performance.
Over a 10-week experimental period max exertional effort did not change, but time to exhaustion was increased. Pedersen is cautious about the simple application of this preliminary research to training. She presents the topic as a question and a point of inquiry calling for more science before coaches and athletes alike adopt the practice. In fact Pedersen cautions against the very thing that Fitzgerald did in his article- immediately prescribe her practice (inaccurately as well) in exercising individuals by telling them not to eat during training. Pedersen instead has shown that exercising twice daily does prove to have positive adaptations due to increased IL-6 levels which in turn increases the bodies ability to burn fat. This is not the same thing as not eating during training, restricting glucose intake and exercising in a state of depleted muscle glycogen are different entities and it is fallible and potentially dangerous to confuse the two.