Carbohydrate Loading for Endurance Sport
Endurance athletes rely upon both carbohydrates and fat as fuel sources during exercise. Carbohydrate becomes the predominant source over fat, the longer the duration and the higher the intensity (1).
Carbohydrates are stored as glycogen in the body. A Carbohydrate rich diet has been proven to increase the body’s glycogen levels as it increases the glucose in circulation, provides fuel for the contracting muscle, stimulates insulin production from the pancreas and improves the conditions upon which glycogen oxidation (burning glycogen stores for fuel) can take place (1).
Athlete’s glycogen stores are depleted during exercise, firstly from muscle glycogen, then liver glycogen, before blood glucose drops and the risk of hypoglycemia develops without additional carbohydrate feeding (1). If an athlete has sufficiently maximized their glycogen stores pre exercise, they will deplete most of their muscle glycogen stores after 2 hours of moderate to intense exercise (1). As a result, there is a strong correlation between the amount of muscle glycogen content at the commencement of exercise and the extent of optimal endurance performance that can be undertaken. For endurance athletes partaking in high intensity sports over 2 hours, maximizing glycogen (fuel) stores prior to exercise is therefore imperative to avoid fatigue and reduced performance, in addition to consuming carbohydrates during exercise to perform beyond the 2 hour mark.
24 Hour Carbohydrate Loading
Studies have shown that with sufficient rest, muscle glycogen stores can be maximized within 24 hours, as opposed to traditional 3-day carbohydrate loading programs (1). Muscle glycogen stores of highly trained male endurance athletes have been shown to plateau after just 24 hours into moderate to high carbohydrate consumption and loading (1).
To maximize glycogen stores, improve performance and reduce fatigue, moderate carbohydrate intake of 6-10g/kg-weight/day, if coupled with adequate exercise rest is required 24 hours before exercise over 2 hours duration (1). Higher carbohydrate intake of 10-12g/kg-weight/day may be required if rest is not achievable (1).
The pre-race meal, 1-4 hours before exercise is imperative to top up glycogen stores. Research has confirmed that meals with carbohydrate content of 1-4g/kg-weight are ideal (1). Choosing carbohydrate foods low in fiber, fat or pure fructose can assist in avoiding gastrointestinal (GI) discomfort during exercise. The closer the meal to the event, the lower the fibre and fat content is recommended. There is some evidence that low GI foods are ideal for slow release energy, such as Oats with strawberries, banana and yoghurt (1).
- Burke, Louise M., et al. “Carbohydrates for training and competition.” Journal of sports sciences 29.sup1 (2011): S17-S27.