Sep 16, 2024
Training Tips by Runzy Director of Coaching Joe McConkey
Common Cause of Bonking at 20 miles
Most readers have experienced or heard of the term 'bonking'. For marathoners, if this occurs (i.e. extreme fatigue and slowing of pace), it typically happens at or around 20 miles in a marathon. Though insufficient training, i.e. lack of volume, speed, and race-specific speed, can certainly be a cause, the most common cause is often over-looked.
Most marathoners who have trained well and are running a smart, appropriate pace on race day yet still experience a sharp drop-off in pace after 20 miles are often simply not getting in enough carbohydrates during the run. Carbs should be around 60% of every meal all the time, and close to 70% in the days leading up to the marathon. Even with this in place, however, if during the marathon the carb intake is lacking, performance will suffer.
A good target to train with and implement on race day is taking in 60 grams of carbohydrate per hour. That's around 3 gel/gu packs per hour! This amount of intake takes practice, as you learn which products, forms (liquid, solid or both), and frequency you can handle digestively and still feel comfortable. The process of trial and error, though, is the same process elite runners have to go through, and can be the most beneficial component of your race preparation.
