Understanding Carbohydrate and Energy Demands for Cyclists

Have your carbohydrate intake match your demands.

Everyone has an opinion on carbs vs fat. From health magazines with the latest fad to the local ‘gym bro’, everyone seems like an expert on the optimal macronutrient profile. In reality, this idea is flawed from the start and macronurients should be consumed to match the demands of the individual. This article will focus on the carbohydrate portion of the mix for cyclists and endurance athletes.

Basics

There are three macronutrients: carbohydrates, fat, and protein. If you are a collegiate athlete, there is a fourth, alcohol. For the rest of us, our diets could be characterized by a pie chart split into three sections representing each macronutrient’s contribution to our diets. In studies, a daily or weekly food journal is kept for researchers to quantify and produce these pie charts.

The idea of using a pie chart to characterize macronutrient profiles is inherently flawed. Why? Because a pie chart is static, it assumes each day’s macronutrient profile is the same. It also fails to inform us on the quantity of food to consume. There is no scale factor to indicate how big the pie is supposed to be.

Cyclist and Carbohydrates

When a cyclist, or any endurance athlete, trains for events they do some combination of low intensity and high intensity exercise. The higher intensity exercise helps to increase VO2max, anaerobic work capacity, sprint efforts. The low intensity work improves other performance factors such as blood volume, muscular adaptations and ensures the rider is prepared for long race efforts.

When a cyclist completes a high intensity effort, they are using carbohydrates to produce 90%+ of the energy used. For lower intensity efforts, the ratio is closer to 1:1, with carbohydrates accounting for about half of the total energy production. This relationship is a well known ‘X’ graph with carbohydrate utilization rising steadily as intensity increases and fat utilization decreasing.

The carbohydrate/fat ‘X’, real world values are generally sloppier, but the ‘X’ does intersect at approximately 50% VO2max

Cyclists should be eating carbohydrates to match their expected workload from training and racing. A human can typically store about 500g of glycogen (essentially long chain glucose molecules) in their muscles and liver for use during exercise. If a cyclist is training to maximize training stimulus and response, then their goal should be to maximize their glycogen stores before their workout. This ensures, to the greatest extent possible, that energy derived from carbohydrates is not a limiter in their capacity to complete high intensity intervals.

Maximizing Glycogen Synthesis

Glycogen synthesis is the process of producing more glycogen from glucose substrate. In the scenario where a rider has used their entire store of glycogen, they should attempt to synthesize ~500g of glycogen from carbohydrates before their next workout. To put this in context, say for training day one, a rider does VO2max intervals, some 6x4min workout at 95% VO2max and comes home completely toast. If their next day’s workout calls for 2x20min at 95% threshold, in order to be adequately prepared, the athlete should look to consume somewhere around 700g of carbohydrates before beginning the next workout. The additional 200g beyond the 500g of stored glycogen are for essential daily processes such as fueling the brain or helping in recovery processes.

It is not so simple to consume 700g of carbs in ~22 hours, assuming the rider works out at the same time every day and with them sleeping for 8-9 hours, there is a 13-14 hour window. This approximates about 50g of carbs per hour, every hour.

Luckily for the athlete, the human body helps to ease the nutritional burden by dramatically increasing glycogen synthesis directly after a workout. Recommendations of up to 1.2 g/kg/hr directly following a workout for up to 2 hours are said to maximize glycogen synthesis rates. For most athletes this is about 200g of their 700g accounted for directly after the workout. During this post-exercise window, when carbohydrates are consumed, there is only small increases in insulin levels as the body is primed with enzymes to utilize and store carbohydrates.

After this short window following a workout, additional glycogen needs to be stored through insulinogenic pathways. The general coaching recommendation is about 0.5g/kg/hr or for a typical athlete somewhere around 37g carbohydrates. My recommendation is to consume 75g of carbohydrates every two hours awake between daily workouts where glycogen stores may be limiting.

Finding Your Carbohydrate Load

The above scenario is for a rider who is completing high intensity efforts day after day. Let’s choose another scenario: following up on the example before, the day after the 2x20min at 95% threshold workouts, the rider is given a rest day by their coach. In this scenario, the rider’s glycogen stores are still empty following their workout, but their glycogen stores do not need to be refilled for ~46 hours rather than the ~22 hours from the previous day. In this scenario, an aggressive carbohydrate loading protocol is not warranted. It is likely the athlete will have full glycogen stores if their eat normal carbohydrate rich meals in the time leading up to their next workout.

Knowing when to eat normal carbohydrate rich meals and when to aggressively increase carbohydrate intake is the key to proper fueling and body weight management for a training cyclist.

The three most common scenarios are as follows:

  1. I have multiple days of high intensity efforts or long rides in a row. In this scenario, it is essential to aggressively consume carbohydrates, specifically the protocol mentioned above: 1.2g/kg/hr for the first two hours following the workout and about 75g per two hours afterwards. Remember, even during moderate intensity exercise, carbohydrates are used. For a long ride, it is likely you will finish with low glycogen levels even if there were no high intensity efforts.
  2. I have multiple days of high intensity efforts or long rides split up by rest days. In this scenario, it is likely that the carbohydrate intake from meals and snacks will allow for sufficient glycogen synthesis. Remember to continue to eat plenty as there is still significant metabolic demands on your system.
  3. I workout once or twice a week with 2+ days rest in between. In this scenario, a normal, balanced diet should be sufficient for your workout needs. Some carbohydrate intake is necessary, but it is not likely that there will be insufficient glycogen for your workout unless carbohydrates are actively avoided.

Realize that as an athlete, at some point in the season, you will be faced with each of these scenarios. So be dynamic and understand which of these recommendations should be followed given upcoming workouts on your schedule.

Last but not least, it is worth mentioning that loading with 1.2g/kg/hr should only be done directly after the workout. This is because our body is primed to synthesize the glucose. When consuming large amounts of glucose at other times, our body instead produces a huge load of insulin and our body attempts to dump the carbs through any pathway possible. This causes excessive fat storage, elevated body temperature, and potentially metabolic disorders in the longer term. Moderate insulin levels due to moderate carbohydrate consumption are optimal for glycogen synthesis.

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