Have you ever been on a challenging ride when your legs suddenly became heavy, and no amount of effort or positive thinking could get your pedals turning again? You may have experienced the ride-ruining phenomenon called bonking, which occurs when you run out of glycogen stores. In a nutshell, you don’t produce energy fast enough to fuel your ride. Bonking sounds funny, but can be very serious. Early signs of bonking include weakness, dizziness, shakiness, light-headedness, irritability, and/or exhaustion. Advanced hypoglycemia can lead to confusion, blurred vision, seizures, hallucinations, and/or loss of consciousness. Bonking during a mountain bike ride can be more dangerous in the backcountry where you can’t easily call for help. Below we’ll discuss some strategies to avoid bonking.
The Science Behind Bonking
Your body requires a lot of energy to ride a bike—not only for your muscles to physically pedal the bike, but also for your brain to focus, balance, and calculate. After you eat, carbohydrates are converted to glucose. Some glucose circulates in your blood, and the rest is further processed into glycogen to be stored in your liver and muscles. Your body can metabolize carbohydrates, fats, and proteins to create ATP energy molecules; however, converting fats and proteins to energy is much more complicated and therefore less energetically efficient than burning sugars. (Don’t worry; we won’t make you relive the details of the Kreb’s cycle.)
During low-intensity exercise, you burn both glucose and fat to provide energy to your brain and muscles. Moderate- to high-intensity exercise requires much more energy per minute, so your body burns mostly glycogen to meet the higher demands. Most people have enough stored glycogen to fuel a difficult workout for up to 60-90 minutes. Bonking occurs when you deplete your stores of easy-to-use glycogen and switch primarily to less-efficient fat metabolism.
Eat Carbs Before You Ride
If you’re planning an intense ride and expect to be on the trail for more than an hour or two, eat about 300-400 calories worth of complex carbohydrates and healthy protein two to three hours before your ride (for example, oatmeal with nuts and fruit or Greek yogurt with honey). Alternatively, you can consume easy-to-digest energy drinks or gels about ten minutes before your ride. This will top off your liver glycogen stores. You can learn more about ride nutrition here.
Pace Yourself for Distance or Intensity
One of the best strategies for avoiding bonking is to slow down. If you’ll be on the trail for more than an hour or two, pedal at a slower, conversational pace. This will allow you to stretch out your glycogen stores, as well as replenish glucose by snacking. If you are going to ride with intensity or you are training for a specific race, that is an entirely different conversation, see our disclaimer below.
Snack While Riding
While it may seem simple to just keep eating while you ride to avoid bonking, the truth is that your body can only process about 30-60 g carbs per hour. Aim to eat about 100-200 calories per hour of easy-to-digest carbohydrates per hour for long rides. Avoid foods high in fiber or fat, since they are more difficult to digest and can cause gastrointestinal discomfort when riding. Bananas, sports drinks, gels, Stroop waffles, or energy bars are good options.
Hydrate While Riding
While dehydration is not the same as glycogen bonking, some of the symptoms can be similar. Dehydration is often accompanied by dry mouth and eyes, muscle cramps, decreased urine, nausea, vomiting, and heart palpitations. For long or high-intensity rides, drinking water is not sufficient for rehydration because you also need to replenish electrolytes. We like Nuun tablets, which contain both caffeine and sodium (360 mmol/L).
Log More Miles
Build endurance gradually. Slow, long rides will help your body become accustomed to using the muscles necessary for mountain biking. When you gradually increase the intensity, you won’t require as much energy.
What to do if you bonk on the trail?
If you think you’re bonking, slow down considerably. If possible, eat some fruit, a bar, or an energy gel. Contact a friend or emergency services if needed. Err on the side of caution—the trail will be here another day! Try to take it easy for a few hours to let your body recover.
Disclaimer: Experts recommend different strategies for fueling before, during, and after mountain bike rides depending on the length and difficulty of the ride, as well as the fitness, body composition, and training history of the athlete. (See our nutrition article from Registered Nutritionist Jamie here.) If you want to optimize your riding performance for racing or extensive mountain biking treks, we recommend consulting with a professional dietician and/or athletic trainer for long-term diet and training plans.