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Bonk Training

bonk trainingThere is a phenomenon known as “bonk training”, which is followed by some very fit athletes. It is not wise if you’re just starting out. Bonk training is controversial. In fact, in the course of normal training most aesthetes takes steps to safeguard against bonking.

Bonk or bonking refers to the point when glycogen stores are depleted. Cyclists call this bonking, endurance runners call it hitting the wall. “Bonk training” is an exercise program designed for weight loss. Bonk training burns more fat and may improve training adaptations and fat burning.


Bonk training appears to have some scientific support. Exercise scientist, Bente Klarlund Pedersen, Ph.D., from the University of Copenhagen, Denmark suggests that athletes, particularly endurance athletes, are able to improve their fitness by completing some workouts in a glycogen-depleted state and some in a glycogen-replete state.

The premise for Dr Pedersen’s suggestions is Interleukin-6. IL-6 is a substance that plays a vital role in the body’s response to tissue stress and trauma. Exercising triggers its release and it is thought to facilitate numerous adaptations to exercise training such as increased fat burning, increased resistance to muscle damage and improved cognitive function. So what’s her point? Dr Pedersen suggests that the main trigger for IL-6 release during exercise is glycogen depletion (bonking). Therefore, bonk training results in greater training adaptations (due to IL-6) than training in a glycogen-repleted state.

So the question is should you bonk train or exercise in a a glycogen-replete state? Well, each has advantages and disadvantages. Consistently bonk training is disadvantageous, and the best training strategy will probably involve a combination of both types of training.


Commonly bonk training involves cardiovascular exercise on an empty stomach first thing in the morning, when glycogen store levels are low, as well as consuming coffee or caffeine equivalent to 2 or 3 cups of coffee and running or cycling at a casual pace (60% of max heart rate) for 20-90 minutes. Glycogen is the only fuel that can supply and support your exercise efforts above 70% of MHR (maximum heart rate). Therefore, when you bonk, your body is forced to dip into your fat and protein stores instead.

The training session is followed by a normal breakfast. Proponents claim this strategy forces the body to “bonk” shortly into the exercise, and subsequently burn more fat to produce energy. It is not clear how medically sound this idea is. Exerting too much energy and “bonking hard,” or experiencing severe hypoglycemia can be dangerous. Bonking may be harmful to your muscles and central nervous system.

Dr Pedersen suggests another method of bonk training. She suggests to perform two workouts in one day. One in the morning, one in the afternoon. Complete the second workout within hours of first workout, such that there is not enough time to replenish your muscle glycogen stores between workouts and without re-fueling with sports drinks and gels.

Below is an excerpt from the September 2002 issue Bicycling magazine about “bonk training”.


It’s morning. Give your fat a kiss good-bye and get to work. 

If you’re normal, well adjusted and sentient, you have to ask why any cyclist would submit himself to “bonk training.” It’s the ultimate in hair-shirt riding. You wake up in the morning, drink two cups of coffee without putting anything else in your stomach, then go for a 60-90 minute ride. The answer: To lose weight. FAST.

Andy Pruitt, clinical director of the Boulder Center for Sports Medicine, has seen plenty of cyclists shed their guts with bonk training. “If I have a patient who’s trying to lose weight- cyclist or not- I have him ride 20-30 minutes before breakfast on a stationary bike at about 60 percent of max heart rate,” says Pruitt. “This ignites your fat-burning metabolism, and it stays lit during the day.” If you have an extra 5-10 pounds to lose, empty-stomach exercise first thing in the morning is ideal, he says.

Bonk training works, according to Pruitt, because there’s no readily available fuel source for your muscles (there’s very little glycogen in the bloodstream when you wake up), so your body has to seek out fuel…stored fat. To get the full effect, you have to maintain an endurance pace; you should be able to converse without panting.

The name of this weight-loss comes from the idea that the training mimics the conditions that lead to the scourge of cyclists- bonking. In fact, true bonking is a danger.

“If you ride like this longer than 90 minutes, your body starts breaking down muscle and protein in organs,” says Liz Applegate, sports nutritionist at the University of California-Davis, cyclist and author of Eat Smart, Play Hard. “Then you’re not just losing fat, you’re weakening your body.” 
Laura Gabrels Metcalf


1. Upon waking, drink 2-3 cups of coffee, up to 45 minutes before cycling. Don’t eat. 
2. Ride at endurance pace- 60-70% of your max heart rate, or a casual pace that doesn’t make you pant when you talk. 
3. Keep it up for 20-90 minutes. 
4. You can do this on consecutive days, but mix in at least one normal breakfast per week. 
5. Eat your typical breakfast as soon as the ride ends. 
6 . Watch the blubber ignite!!


Since bonking refers to when your body runs out of fuel or you become hypoglycemic, it does NOT feel good. Some of the symptoms include those of hypoglycemia:

  • general weakness
  • dizziness
  • confusion
  • nausea
  • slowed pace
  • fatigue
  • lack or, or no, power
  • irritability
  • When the brain is starved, it may misrepresent incoming images, such that you suffer hallucinations. Instead of seeing rain drops you might something entirely different. Needless to say, it becomes somewhat more dangerous when you can’t see what’s going on, especially when you’re on a bike.

In Triathlon Revolution: Training, Technique, and Inspiration, Terri Schneider writes this: Some people working through a bonk can keep going by basically shutting down their brains and plowing forward. It’s no pretty to watch – and generally makes for an experience you wouldn’t wish on your worst enemies.

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