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Learning Activity 3: Carbohydrates and Endurance Sports
Mikia French
Liberty University
HLTH 645 Performance Nutrition for the Physically Active
March 2, 2023
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The athlete is a 28-year old male wanting to run marathons. He is in good health. He
has been running 5K and 10K races for the past two years but is afraid of “hitting the
wall” or experiencing some other exhaustive phenomenon.
1. The physiological response of carbohydrate loading in sports.
Carbohydrate used by exercising muscle can come from stored muscle glycogen
or from glucose that is brought into the muscle from the blood.1 The idea behind carb
loading prior to a big event is to increase muscle glycogen to higher than normal
levels in order to increase and sustain energy during endurance events. It serves as a
purpose to maintain muscle glycogen so it is not depleted quickly, falling to very low
concentrations. The physiological response that happens is positive when done
correctly. This energy is a necessity for endurance athletes, especially marathon
runners who must maintain a constant movement for long periods of time.
2. The process of carbohydrate loading.
The recommendation for total carbohydrate intake for athletes in training is 3 to
12 g/kg of body weight daily, with the assumption that caloric intake is adequate.1
Each athlete is different therefor ratios and intakes must be tailored to the individual.
Endurance athlete, much like the client discussed will need high amounts of carbs,
between 6 to 10g/kg in order to maintain high levels muscle glycogen during rigorous
training routines.1 It is a nutritional strategy of super compensation to increase muscle
glycogen stores. The concentration of carbohydrate is dependent upon the individual,
too much and it could cause GI distress.1 “Seven days prior to the event or
competition, exhaustive exercise is performed for 3 ½ days in combination with an
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extremely low-carbohydrate diet.”1 That is the depletion stage, where carb stores are
depleted and remain low due to low carbohydrate intake. This stage is followed by the
repletion stage which is 3 ½ days of very light to no exercise and a diet high in
carbohydrates.1 In this stage the glycogen-starved muscles “super compensate” and
the maximum the glycogen stores are the result.1
3. The advantages and disadvantages of various carbohydrate loading techniques.
Some of the disadvantages of carb loading comes from the various adverse effects
the athlete may experience during the depletion and repletion stages. Some of these
effects include irritability, hypoglycemia, fatigue, increased risk for injury, and
gastrointestinal distress.1 With the excess storage of glycogen the body will also retain
more water, this can cause weight gain. Carbohydrates are water-soluble, this is the
reason for the water retention.2 The carb loading techniques are not simple and “one
size fits all” therefor many mistakes can be made in the process. Carb loading
techniques only work well for specific types of exercise and it is not an effective
method for short durations of exercise.
Some advantages include the capacity to “super compensate or over stock”
glycogen stores in the body for use during prolonged physical activity. Research has
shown that carb loading may improve performance by 2-3% for exercise lasting more
than 90 minutes.3 Another advantage is that this practice can delay the onset of fatigue
and muscle failure. It has also been proven to increase endurance and improve
stamina.3
4. The timing, amount, and listing of appropriate food sources for carbohydrate
loading.
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The timing is dependent upon which carb loading technique the athlete is going to
use. We will discuss the week long carb loading cycle. It begins a week prior to the
event, for the depletion stage (3.5 days) the athlete will continue exercising while
consuming a low carb diet, this will depletion muscle glycogen stores. During the
repletion stage the 3 ½ days prior to the event there will be little to no exercise and
about 70-85% of calories will come from carbohydrates.3 This restores muscle
glycogen, maximizing the supply. The calories that come from carbohydrates should
come from complex carbs, not simple carbs. Complex carbs or polysaccharides offer
many health benefits, simple sugars can be naturally occurring (fruits) or added by
manufacturers.2 When they are added they often hold no nutritional value and are just
empty calories.2 Appropriate foods would include fruits such as berries, oatmeal, nut
butters, cheese, sweet potatoes, rice, quinoa, whole wheat bread, grilled chicken,
salmon, steamed or grilled fresh veggies, and eggs. Sodium intake is also an
important consideration. Choose foods that are familiar.
The idea is to plan ahead, pack plenty of carb rich snacks like energy bars for the
event. The night prior it is suggested to not eat a dense meal, so consuming healthy
snacks throughout the day would be beneficial. This will allow the athlete’s body time
to rest and digest prior to the event, mitigating any potential for gastric upset.
5. Any additional information needed to explain the why, how, when, and what of
carbohydrate loading.
There are several different carb loading methods or variations it is important in
order to maximize performance that one is followed precisely. The major differences
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between the various carb loading methods include the duration and the amount of
exercise.3 All programs use a short-term, high-carb diet while temporarily decreasing
exercise.3 There are several mistakes that are common but can be easily avoided with the
proper research and knowledge. Carb loading is not something that should be done when
it is not necessary, it is beneficial for long term physical activity, not for short durations
of exercise. Another mistake is not consuming the right amount of carbohydrates, it
would be very helpful to record what is consumed and there are many apps that can assist
in tracking macronutrients. Without recording this information it opens the door for the
mistake of consuming too much or too little. It is also not a wise idea to introduce new
foods while carb loading.
References:
1. Dunford M. Nutrition for Sport and Exercise. Cengage Learning; 2021.
2. Catharine Anna Kebles, Hemric M. Omega Z Diet for Weight Loss.; 2021.
3. Carb Loading: How to Do It + Common Mistakes. Healthline. Published February 11,
2018. https://www.healthline.com/nutrition/carb-loading#TOC_TITLE_HDR_3
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