Carbohydrates Needs for Endurance Sport
If you are an endurance athlete who trains or competes in events over 2 hours at a high intensity, you have specific carbohydrates needs. Studies have concluded that the consequences of inadequate carbohydrate intake by endurance athletes include immune depression, reduced mood and motivation, early onset of fatigue and reduced performance.
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. Carbohydrate is stored in both muscle (~350-700g) and liver (~100g) as glycogen.
A Carbohydrate rich diet has been proven to increase the body’s glycogen levels, as it increases the glucose in circulation and provides fuel for the contracting muscle. An 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.
If an athlete has sufficiently maximized their glycogen stores pre-exercise, they will deplete most of their muscle glycogen stores after 2hours of moderate to intense exercise. 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. Additional carbohydrate is required from the onset of endurance exercise to prevent depletion of liver glycogen stores, to fuel exercise over 2hours, and prevent fatigue.
Fatigue is defined as the inability to maintain the required or expected level of power output and is common in endurance events of significant intensity over 2 hours. We now know that this is often the result of depleted glycogen stores and reduced concentrations of blood glucose, along with inadequate carbohydrate intake.
If you exercise at a very slow pace you are burning fat as well as carbs and these levels are not applicable as your carbohydrate storage (glycogen) will last for longer than 2 hours. However Medium to high intensity exercise over 2 hrs uses predominantly carbs to fuel exercise, not fat, and at 2 hrs all your stores will run out.
24 Hours before Endurance Exercise
To maximize glycogen stores, moderate carbohydrate intake of 8-10g/kg-weight/day, if coupled with adequate exercise rest is required 24hours before exercise over 2hours duration. Higher carbohydrate intake of 10-12g/kg-weight/day may be required if rest is not achievable. For a 55kg female, 8-10g/kg-weight/day would equate to 440g-550g carbohydrates in the 24hours pre exercise. The traditional 3-5 day carbohydrate loading regime including carbohydrate depletion followed by rest with carbohydrate loading is no longer supported and has been replaced with the above 24 hour method.
Pre Race Meal, 1-4 hours before Exercise
A pre-exercise meal to further top up glycogen stores, before exercise over 2hours in duration is needed. Recommend intake of 1-4g/kg-weight of carbohydrate, Low-Fibre, High-GI with some protein and a little fat. The closer the meal is to exercise, the lower the amount of fat and fibre is recommended.
Consume 60-90g/hour of carbohydrate, from the commencement of exercise, to avoid fatigue. Choose High-GI, Low-Fibre and preferably a glucose+Fructose or Glucose+maltodextrose combination for better absorption and lower GI issues. Add protein if >60g/hour is not achievable. Ideally, consume 1x800ml sports drink per hour (66g carbs) along with an additional supplement from table 3 below (20-39g carbs).
Avoid flavor fatigue by mixing up carbohydrate sources. Support crew availability to assist athletes will ensure optimal consumption. Sports drinks should contain 6-8% carbohydrate, supplied at room temperature to avoid GI issues.
Post Exercise Meal
After exercise, athletes need to restore their bodies glycogen levels to prepare for subsequent exercise. The most rapid rates of glycogen re-synthesis occur in the first hour after exercise, due to the increased permeability of muscle cell membranes. During this time carbohydrate feeding has shown to increase muscle glycogen stores. As a result, carbohydrate, preferably high-GI for quicker absorption, is recommended after exercise to replenish maximum glycogen stores during recovery, along with 21g high quality protein to aid muscle recovery:
- If no further Exercise within 24hours: 1.0-1.2g/kg-weight per hour is recommended within the first hour followed by daily carbohydrate requirements of 6-10g/kg-weight/day
- If exercise within 8hours: 1.0-1.2g/kg-weight per hour is recommended for first 4hrs (55-66g for a 55kg athlete), the first consumption being within the first hour, followed by daily carbohydrate requirements of 6-10g/kg-weight/day
See below some high carbohydrate meals suitable for post endurance exercise Recovery which include ~20g high quality protein.
|High Carbohydrate Post Exercise Meals||Qty||Carbohydrate||Protein|
|Instant oatmeal Porridge with 400ml low fat milk||100g||88g||25g|
|Museli with 1 cup low fat milk||100g||90g||18g|
|220g Baked Beans, 2 slices toast||1||78g||18g|
|Low fat chocolate milk||500ml||61g||16g|