How to avoid the bonk on a long run or ride
The bonk has a way of arriving without warning. One kilometre you feel steady, the next your legs are heavy, your head is foggy, and your pace collapses. Most endurance athletes have been there, whether at the 28-kilometre mark of a winter marathon or deep into a five-hour ride through the Yarra Valley. The crash is not mysterious. It has clear causes rooted in fuel availability, pacing, or environmental stress, and it can be defended against with well-rehearsed habits.
Hitting the wall, blowing up, going into the red. Endurance athletes have many names for glycogen depletion, and the vocabulary reflects how common the experience is. A rider rolling through the Adelaide Hills on a Sunday loop is fighting the same metabolic battle as a trail runner grinding up a Blue Mountains fire trail in January. The mechanics are similar, even if the surfaces and bikes differ.
Australian conditions add their own texture. A December long run in Brisbane can begin at 6 a.m. with the mercury already nudging 26 degrees, and finish in full sun an hour later. Local athletes learn quickly that heat, humidity, and remote terrain change the fuel equation in ways that a cool European spring does not. The bonk is highly preventable once you understand what triggers it and build a routine around your specific conditions.
This piece pulls together the practical side of avoiding the bonk, from base training and mid-effort fueling to pacing and reading your body. The aim is a set of principles you can adapt to your own long runs, rides, and races across the country.
What the bonk actually is and why it happens
Glycogen is the stored carbohydrate your muscles draw on when working at moderate to high intensity. When those stores run dry, the body shifts to fat as a primary fuel, which is slower to convert and produces less power. The result is the sudden heaviness, foggy head, and slow legs that runners and riders call the bonk. Blood sugar can also drop, compounding the cognitive symptoms.
Three things accelerate glycogen burn: starting too hard, failing to top up carbohydrates during the effort, and exercising in heat without adjusting pace or fluid intake. In places like Perth or inland Queensland, where summer rides regularly cross 35 degrees, the body pulls extra blood to the skin for cooling, draining glycogen faster than the same ride in milder weather. The bonk is rarely a single failure but the sum of a pace that was a little too ambitious, a fueling window that opened too late, and conditions that pushed sweat rate higher than planned.
Building a weekly base that protects glycogen stores
Long efforts are easier when the body is conditioned to store and mobilise glycogen efficiently. That happens through easy volume, periodic long sessions, and enough intensity to train the metabolic pathways without overreaching. Athletes who skip long efforts often arrive at race day under-fuelled at the cellular level.
In practice, that means keeping most weekly mileage at a conversational pace, with one or two sessions that push the duration toward your goal event. A cyclist targeting a 200-kilometre Audax will benefit from regular three to four-hour base rides, while a trail runner preparing for the Six Foot Track needs a handful of 25-to-30-kilometre weekends. The weekly diet should also include enough complex carbohydrates to keep stores topped up: rice, pasta, oats, potatoes, and dense breads. A workable starting point is 5 to 8 grams per kilogram of bodyweight per day, alongside consistent sipping through the day rather than catching up in the evening.
Mid-effort fueling: the practical numbers
The body can absorb roughly 60 to 90 grams of carbohydrate per hour during moderate-intensity exercise, more if the gut is trained and multiple transportable carbs are used. Waiting until the halfway point to eat is one of the most common ways athletes bonk. A rider two hours into a loop around the Macedon Ranges needs to have been sipping from a bottle well before hunger arrives.
A practical plan starts with 30 to 60 grams of carbohydrate per hour for efforts under two hours, rising to 60 to 90 grams for anything longer, from a mix of sports drinks, gels, chews, and real food. In Australia, Spring Energy gels and Tailwind mixes are easy to find at local running stores, alongside banana halves or jam sandwiches. Electrolytes matter as soon as sweat rate climbs. Sodium losses above 800 milligrams per hour, common on a hot ride through the Barossa, can cause cramping that masquerades as a fuel problem, so adding 500 to 1000 milligrams of sodium per litre of drink keeps absorption steady. The exact brand matters less than the routine: your gut needs to be rehearsed, and your timing needs to be automatic.
Reading your body during the run or ride
Bonks rarely arrive without warning. The signs show up early: a slight dip in pace, an urge to slow on a climb that would normally feel manageable, a small wobble in focus. Athletes who learn to read these signals can intervene with a gel, a drink, or a pace adjustment long before the crash sets in.
Mental discipline is part of this. Long efforts require a quiet attention to small changes in the body, the same steady awareness that riders develop in disciplines like endurance horse work, where reading subtle cues is the difference between finishing strong and running out of fuel. A quick check-in every 20 to 30 minutes, covering pace, hunger, thirst, and breathing, is usually enough to catch a developing problem.
Pacing and effort to keep the tank from emptying
Pace is the most controllable lever in avoiding the bonk. Starting a long ride at threshold, because the legs feel fresh, is a reliable way to arrive at the 90-kilometre mark with empty tanks. The first hour should feel almost disappointingly easy. A heart rate or power output kept 10 to 15 percent below your sustainable ceiling buys an enormous amount of glycogen later in the effort.
Riders have a useful phrase: ride the first half with your head, the second half with your legs. The same applies to long runs. A steady opening on a hilly loop through the You Yangs leaves enough in the tank to finish the climbs strongly. Wind and heat deserve a seat at the pacing table too. A headwind out will cost more than the tailwind returns, and in summer, dropping effort by 5 to 10 percent on hot days is a realistic adjustment to a body already diverting resources to cooling.
A practical fueling framework
| Effort duration | Carb intake per hour | Fluid per hour | Sodium target | Sample sources |
|---|---|---|---|---|
| Under 90 minutes | 20–40 g | 400–600 ml | 200–400 mg | Sip of sports drink, small gel, water |
| 90 minutes to 3 hours | 40–60 g | 500–800 ml | 400–700 mg | Drink mix, 1–2 gels, banana or bar |
| 3 to 5 hours | 60–80 g | 600–1000 ml | 600–900 mg | Stronger mix, regular gels, real food, electrolytes |
| Over 5 hours | 80–100 g | 700–1100 ml | 800–1100 mg | Multiple sources, dense food, frequent sipping |
These numbers are starting points, not rules. Heat, intensity, body size, and gut training all shift them. A winter three-hour ride through the Dandenong Ranges will sit at the lower end, while a summer ultra in the Pilbara will demand the upper end plus aggressive cooling.
Training the gut to absorb more fuel
The gut is trainable, and most athletes underuse it. A stomach that cannot tolerate 60 grams of carbohydrate per hour in training will not magically handle it on race day. Conversely, a gut that has practised absorbing a mix of maltodextrin and fructose across a dozen long rides will process fuel efficiently when it matters.
Start small during training, perhaps 30 grams per hour, and build up over weeks. Vary the sources: gels on one ride, real food on the next, a drink mix on another. Most people find that a 2-to-1 or 1-to-1 ratio of glucose to fructose is the sweet spot. Caffeine is a useful tool but not a fuel source. A dose of 100 to 200 milligrams can sharpen focus and reduce perceived effort, particularly in the final third of a long effort, and works best when used strategically rather than daily.
Pick one long effort in the next seven days and treat it as a fueling rehearsal rather than a test. Start at an easy pace, eat and drink on a timer from the first 30 minutes, and log the result. Repeat the same routine on a second long effort next week, tweaking the numbers slightly, and notice what changes in your legs and head.