Many long-distance athletes are familiar with the concept of bonking or “hitting the wall.” It’s the sudden, severe fatigue that can stop a long run or race in its tracks, and it’s common. Why does this happen, and how can runners prevent or reverse a bonk?

What causes bonking?

Bonking during a run occurs when an endurance athlete’s glycogen stores become depleted. Glycogen is a form of glucose (sugar) — the body’s main source of energy.

It’s created by breaking down carbohydrates, and it provides a consistent source of energy during exercise, so when it runs out, you bonk.

Why is bonking bad?

Bonking can do more than just derail a single training run or a race. This phenomenon has the potential to cause more significant problems for runners or other endurance athletes, including muscle loss, immune suppression, and training disruption.

Muscle loss

Bonking could lead to muscle loss, according to a review of the effects of glycogen availability on endurance exercise. Some studies have reported that exercising with low glycogen stores may lead to an increase in muscle protein breakdown. Other research suggests that performing endurance exercises with reduced muscle glycogen could impair post-workout muscle repair and recovery.

Immune suppression

There’s some evidence that training in a glycogen-depleted state increases the level of stress hormones in the body; this hormone imbalance may impair the normal functioning of the immune system. This may help explain why marathoners experience up to 72 hours of immune dysfunction after a race when bacteria and viruses can gain the upper hand.

Training disruption

Runners who hit the wall may find themselves limited to a walking pace or even unable to continue their planned run. After experiencing a bonk during a run, you may feel discouraged about your training and take some time to get back into the groove of long runs. Try not to let bonking throw you off for long: While a short rest period (just two weeks of detraining) has been shown to reduce VO2 max and muscle strength in endurance runners, muscle endurance is preserved.

Can you prevent bonking?

Endurance athletes may take different nutritional approaches to try to prevent bonking. Some athletes maximize their glycogen stores by following a high-carbohydrate diet. The International Society of Sports Nutrition recommends athletes eat 8 to 12 g/kg of carbohydrates per day to maximize their glycogen
stores. For a 150 lb (68 kg) athlete, that means eating somewhere between 544 and 816 g of carbs per day.

Some athletes may take the opposite approach and follow a low-carb diet. The goal is to encourage the body to burn fat for fuel, rather than glycogen, to prevent bonking or hitting the wall. Consider working with a sports nutritionist to find the right eating plan to prevent bonking on your long runs.

How to recover from bonking and continue your workout

If you feel like you’re starting to bonk on a run, there are a few tricks that could help you recover and complete your race or training session. You might want to consider:

• Consuming carbohydrates. Since the body breaks down carbs into glucose, enjoying a carbohydrate-rich snack could help refuel your glycogen stores. Some popular options include sports bars, trail mix, or energy chews and gels.
• Drinking some water. Glycogen bonds to water in your cells, so consider washing your high-carbohydrate snack down with some water.
• Trying electrolytes. Electrolytes can help prevent glycogen depletion and promote glycogen replenishment. Some options for replacing electrolytes include sports drinks, sports gummies, and electrolyte tablets.
• Taking a break. If you feel a bonk coming on, pause your workout and let your heart rate come down. Wait until you feel recovered before continuing.

Is it safe to continue working out after bonking?

When muscle glycogen stores are low, athletes may hit the wall and experience impaired performance and low blood sugar (hypoglycemia).

Hypoglycemia is a potentially dangerous condition that can leave you feeling shaky, dizzy, nauseous, or in more severe cases, confused and uncoordinated. If your bonk includes these symptoms, it’s a good idea to stop your workout and seek medical help.

Recover after long runs with Ice Barrel

Cold water immersion is a great addition to an endurance athlete’s post-workout recovery routine. It’s well-established that a cold plunge supports muscle recovery, reduces inflammation, and calms your mind.