ENDLESS ENERGY
EXPERT ADVICE ON BEATING THE ‘BONK’
The ‘bonk’ is a catastrophic loss of energy that halts us in our tracks. So just how can we stop disaster before it strikes?
It didn’t happen on my first long ride, but years after I started cycling. It wasn’t even a mega-ride — just a classic Box Hill loop of three hours.
Before that ride, I had done a Park Run with my friends. Then we changed gears and went for our Saturday spin. I tried to eat regularly (my personal rule of thumb was one bar per hour), but it wasn’t enough. On the way back, we started to push a bit harder and, all of a sudden, my energy switched off. My vision got blurry, I felt like I was passing out, and my energy indicator fell to empty. I was cooked.
A little uphill road that I usually didn’t even notice suddenly felt like climbing Alpe d’Huez. I zig-zagged left and right, with the lowest cog I had on my cassette. My friends flew past me. I reached the top, minutes down. When I got off the bike, I was still shaking, my heart pounding at a high speed.
“Oh, man, I don’t know what happened!” I told my friend Colin.
“You bonked!” he replied.
You bonked. That was the first time I’d heard the word in English. In Italy, my home country, I had known it as la crisi di fame (the hunger crisis). I had always avoided it with my one-bar-per-hour rule. However, when you ride at a higher intensity, and you don’t eat enough, not even bars will save you.
Sometimes, after a bonk, you can’t even make it home, not even when you live two miles away. The only thing you can do is sit down and call somebody to pick you up, or wait for a very long time before resuming your ride.
My friend Colin, who clearly knows a thing or two about bonking, remembers when he did the Maratona Dles Dolomites gran fondo in 2016. After just 60 kilometres of a total 137km and 4200 metres of vertical elevation, he had to wait close to an hour at the aid station before being able to move on again. He eventually finished the event, for which he’s always been heavily indebted to Italian food. In January of this year, Marco Viappiani bonked around 3km from the end of a 10-hour, 205km Rapha audax. Despite having consumed several bars, gels and sweets during the ride — plus beans on toast and a sausage roll from the aid stations — the hunger still got him.
“After the second stop, a guy from our group started to push a bit more to catch some other guys,” he says. “But when we reached them, they put the hammer down. At that pace, I had a hard time reaching the nutrition in my pockets. Then I felt the feeling of a car engine stopping. I couldn’t even tell the other guys I was stopping. I just stopped at the side of the road.”
HEART OF THE MATTER
We usually define the bonk as the moment where we ‘hit the wall’ or — in scientific terms — when the glycogen stores in our muscles and liver empty, and we can’t keep up with our energy expenditure. The first studies on carbohydrate depletion and drops
in blood-sugar levels were done in 1924 and 1925. Scientists found that runners in the Boston Marathon had reduced blood sugar levels after the 1924 race. The following year, with adequate carbohydrate feeding, their levels of blood sugars were maintained, and their performances increased.
In almost 100 years of research, we’ve learned a few more things about the bonk. Most importantly, we’ve discovered that there’s not only one type.
“There are many causes,” says Jiri Dostal, head physician for the Centre of Sports Medicine in Prague and consultant to the Czech Olympic Committee. “The bonk is a human reflex and scientists still debate just how much it’s influenced by a person’s own will.”
The reflex, explains Dostal, is caused by the disruption of the homeostasis level, which is the maintenance of a constant internal environment in the human body. This change causes growth in perceived exertion and a decrease in performance. How the reflex is produced is ‘simple’ — but its effects are notorious.
“Your neurons sense local status in the muscles, heart, lungs, stomach and all other organs,” says Dostal. “All the signals are then processed in the brain, and if the information shows a critical situation in some organs, then the brain shuts down the non-working muscles first, and then the active muscles by decreasing the activity of motor neurons and vasoconstriction.”
In other terms, the bonk is not a bad thing; it’s a warning. Indeed, we should actually see it as a friend. “It might save your life,” confirms Dostal.
THEORY AND PRACTICE
The ‘hitting the wall’ theory was elaborated on through several studies during the late 1960s and early 1970s, the most influential of which was Diet,MuscleGlycogenand EndurancePerformance, by Jan Karlson and Bengt Saltin, two physiologists from Stockholm.
At a team camp in December 2019, Team Ineos’s Cameron Wurf didn’t just hit the wall, he hurtled into it. Along with Geraint Thomas, Dylan van Baarle and Ian Stannard, he had decided to do a lap of the entire island of Mallorca. “We decided to treat it like a team time trial in the second half,” the Australian explains. “For this 150km, we averaged 50kmph. Obviously, that burns some serious fuel. I remember thinking, ‘Just survive until 300km. From there, it’s only 10km to the hotel.’”
It was not to be. “At 300km, as I peeled off the front, I went completely lights out and the train left me behind.” He was so bonked, in fact, that he kept riding right past the hotel — despite the team bus and cars parked out front. His coach wasn’t sympathetic: “As punishment for getting dropped in those last 10km, my coach made me change into my running shoes and run 10km [Wurf is also a professional triathlete], give me some time to learn my lesson and ensure I eat correctly next time we do a lap of Mallorca.”
The bonk can also be caused by a Relative Energy Deficiency (RED), which is connected to both eating disorders and low energy availability. The bonk can, in fact, be laid down days before the actual race or ride. It doesn’t matter how well and how much you eat during the event – if you haven’t fuelled correctly in the build-up to your ride (even only for a few days), or you’re always in an energy deficit, these factors can lead to a ‘bonky’ ride.
Even a mild cold, some inflammation, significant stress, or a fever can have an impact on your body’s ability to utilise fat and carbohydrates. They can, in fact, lower your ability to burn fat for fuel (fundamental to counterbalance the needs of carbs on long events), increasing the utilisation of carbohydrates during exercise and depleting glycogen stores in the muscles. That’s a perfect mix for a bonk if that happens just a week before the event.
Furthermore, riders who train hard for several days in a row can also be affected by
‘low metabolic flexibility’ — which is created by a massive demand of carb ingestion that the intestine can not handle.
A more recent theory known as the ‘Dempsey metabolic reflex’ associates a decrease in performance with the accumulation of fatigue in breathing muscles like the diaphragm, intercostal muscles and accessory respiration muscles in the neck and the torso. This fatigue can cause blood-flow constrictions in muscles, changes in cardiac output, oxygen uptake and a decrease in performance.
FIRE AND ICE
Hot and cold temperatures are also causes of two specific bonks. Colder temperatures require higher energy demand and an increased delivery of food, and are associated with a higher oxygen demand for a given power output. Yet, in freezing temperatures, we tend to eat less because, with cold hands, it becomes harder to get the nutrition from our rear pockets. This is also the case when a race becomes hectic, or when the length of it calls for a higher amount of food to be consumed. If you put them all together, you have a recipe for disaster. A dramatic example of the cold temperature bonk is Mathieu Van Der Poel’s at the World Championships in Yorkshire last September.
With hot temperatures, on the other hand, the enemy is dehydration, which is not only connected to fluid loss. As Robert Gorgos – head of nutrition for the professional cycling team BORA-Hansgrohe and a former professional cyclist himself – explains: “Dehydration causes a restriction in the transport of glucose and other energy sources through your intestine into your bloodstream and to the cells.”
Finally, you can dig yourself into a bonk by overdoing one of the cyclist’s favourite drinks – coffee. “Caffeine, especially in combination with fast sugars, could lead to a spike and subsequent fall in blood glucose,” says Gorgos.
In the majority of cases, the bonk causes a growing sense of fatigue compared to speeds and power outputs that are usually easily sustained. The effect on the heart rate is different and complex: sometimes it lowers and sometimes it rises.
“There are different signs to look for: the reduction in pace for the same heart rate, the increase of heart rate at the same pace, dry mouth and a slower body movement or reaction,” says Gorgos. There could be several causes for any difference in physiological parameters, and there’s no way to know the bonk is around the corner.
That’s why the best way to fight a bonk is to prevent it happening in the first place, explains Gorgos. “You can avoid the bonk in different ways: pacing yourself during the ride, eating carbohydrates before, during and after every high-intensity training ride, go really easy on the ‘train low’ days” (days when athletes deliberately train with low glycogen stores to trigger the use of fat as a fuel source instead of carbohydrates), eat a carbohydrate-rich diet and maybe try branched-chain amino acids (BCAAs) in the second part of long rides. BCAAs depletion could lead to elevated levels of the amino acid tryptophan in the brain, and that could depress the central nervous system.
“Don’t overthink nutrition. A balanced, carbohydrate-rich diet, together with structured training that includes hard and easy days, gives you a good chance to avoid bonking. And eating more carbohydrates two days before a very long or tough race or workout is always a good idea.”
NO SWEAT
Dehydration isn’t easy to detect before it happens. On top of the feeling of being thirsty (which can mean it’s already a bit too late), its classic symptoms include cramps, dizziness and the inability to sustain an effort that usually is not hard to perform.
Lisa Nijbroek, head nutritionist for the WorldTour cycling outfit Team Sunweb, explains how the team uses advanced sweat tests for their riders, from UK specialists Precision Hydration. “With the Precision Hydration test kit, we can measure their sodium losses in their sweat, and that’s a test we do once because it’s a fixed number and does not change so much. The question that remains is then how much per hour do they sweat?”
That depends on external temperatures and humidity levels, as well as on the intensity of the individual training session or race. But cold temperatures can make riders forget to drink enough.
To have a better understanding of their hourly sweat loss, Team Sunweb’s riders are required to weigh themselves before and after the training sessions and calculate the amount of liquid consumed during that session.
“A lot also depends on the hydration levels at the beginning of the session,” says Nijbroek. (The rule of thumb is to check the colour of your urine: the darker it is, the more dehydrated you are.) “If you start already dehydrated, you need to drink more, while if you start already well hydrated, then the general guidelines are okay. For example, in the team, our rule is to have at least one 500ml bottle of water or sports drink per hour. And that’s the minimum rule we have for really cold temperatures. But if you feel like you sweat more and lose more sodium, I advise that you do a sweat test.”
Once you’ve experienced the bonk, you’ll do all you can to stop it happening again. It can attack from many different angles, pouncing on misjudgments in food and drink intake, intensity of effort and pre-ride preparation. Yet knowing what to look out for is the best step to ensuring that you never hit that wall again.