Why are carbohydrates important remember metabolism for sprinting or working out at a high-intensity?

Running is simple, we put one foot in front of the other, and allow it to happen naturally.

That is how we start, but once we get into running a little more, we want to learn more about how to improve our speed by increasing our step frequency and step length, we want to know which foods will give us the most energy on our runs, and we want to understand which energy systems we use in a 400m sprint.

There are so many questions, and there is so much to learn about running. If you want to be the best runner you can be, these are areas you probably want to start paying attention to.

If you want to increase your running speed, you probably already know that it is actually not your speed holding you back, but your aerobic endurance, and while knowing what to eat before, during, and after each type of training run is very important, I should firstly introduce the physiology of energy metabolism during different levels of exercise.

If you need the aerobic energy system explained, you are in the right place. Today we we break the three energy systems down, so you can learn how you have the energy to sprint as fast as you can, how the anaerobic energy system works, and what the aerobic energy system is.

Each of these play a role in us being able to run faster, so let’s learn more about them:

Why do I need to know about energy metabolism?

Knowing the predominant energy system you are using during your workouts will help you determine your recovery needs for nutrition and rest.

Energy is stored in the body in various forms of carbohydrates, fats, and proteins as well as in the molecule creatine phosphate.

Carbohydrate and fat are the primary sources of energy, with protein contributing a minimal amount under normal conditions.

Adenosine triphospate (ATP) is the body’s usable form of energy. The body uses 3 different systems of metabolism to transfer stored energy to form ATP.

What are the 3 Energy Systems?

The Phosphagen System

The phosphagen system of energy transfer does not require oxygen (anaerobic) and is called upon when there is a sudden increase in energy demand such as starting a workout, starting explosive hill sprints, or throwing a discus.

It is the most direct and quickest form of energy production but can only supply enough energy for a short burst intense activity like a maximum weight lift or a 5 second sprint.

This system relies on the availability of creatine phosphate, which is in limited supply and is depleted quickly.

When creatine phosphate is used up, the body must call on other systems of energy transfer to sustain continued activity.

Glycolysis (anaerobic) System

Another system that doesn’t require oxygen is glycolysis, also known as the lactate system.

This system provides enough ATP to fuel 1 to 3 minutes of intense activity when adequate oxygen isn’t available for aerobic metabolism.

Lactate or lactic acid is something that most runners have heard of and may even fear because of its connection with sore muscles and fatigue.

Hopefully the following explanation of glycolysis will help you picture what is going on.

Glucose is the only fuel that can be used during glycolysis, which literally means the breakdown of glucose.

This breakdown creates ATP as glucose is converted into 2 molecules of pyruvate.

Now:

Hydrogen is also produced during this process and if oxygen is present, the aerobic system (explained next) can use hydrogen and pyruvate to produce more ATP.

However, often times the aerobic system cannot keep up with the excess hydrogen being produced so instead the hydrogen combines with pyruvate to form lactic acid.

Lactic acid then enters the bloodstream and is cleared by the liver.

The point at which the production of lactate is faster than lactate clearance is called the lactate threshold, also referred to as the anaerobic threshold, when lactic acid begins to accumulate in the blood.

The increased acidity of the blood inhibits the use of fatty acids for energy production through aerobic metabolism and thus increases the body’s reliance on carbohydrate and glycolysis.

As blood lactate levels continue to rise and carbohydrate stores become depleted, the muscles begin to fatigue and performance is diminished.

An athlete can increase their lactate threshold through adaptations made during proper endurance training.

This is where my knowledge of the lactate threshold ends and I leave it to the expert coaches to figure out the best way to do that!

I will say though that one of those adaptations is the increasing the efficiency of the aerobic system.

The Aerobic System

The aerobic system can use carbohydrates, fats, or proteins to produce energy.

Energy production is slower, but more efficient than the other two systems.

As you can tell by the name, the aerobic system requires that there be adequate oxygen available to the working muscles.

Therefore this system is used more heavily during low-intensity activity, but actually, most of our races, even a 5k mostly use the aerobic system.

One key highlight of aerobic metabolism is the ability to burn fat as fuel.

Our bodies have a seemingly unlimited capacity for storing fat and fat provides over twice as much energy per gram than protein or carbohydrate, making it a very attractive choice for energy production.

In prolonged activities where intensity is low, the body will use fat as a main energy source and spare the use of muscle glycogen and blood glucose so that it is available for use if exercise intensity increases and oxygen availability is decreased.

Keep in mind that aerobic metabolism doesn’t use one substrate exclusively.

Although you may be burning mostly fat, a steady supply of carbohydrate is still necessary for the breakdown of fat into an energy source.

What’s the bottom line?

Just like the aerobic system isn’t exclusive to one substrate, energy metabolism isn’t exclusive to one system.

All 3 systems are working simultaneously to fuel the body during exercise.

Remember this:

However, certain characteristics such as exercise duration and intensity will determine the predominate system and thus how long the activity can be performed at that level.

Other factors that influence what substrates and systems are being used include the fuels that are available, the fitness level of the athlete, and the nutritional status of the athlete.

These factors may change over time and through training so just like overall nutrition, energy metabolism is very individualized and dynamic.

What Should I Eat Before Running Workouts?

If you are still wondering about eating before a run or workout, make sure you go back and read more about when you should and should not eat before.

One big reason for having adequate fuel before a workout, as well as on a daily basis, is to prevent the use of protein as a fuel source.

Protein is usually spared from being used as an energy source and is used predominately by the body for tissue maintenance, growth, and repair.

However, when glycogen stores are depleted, amino acids from muscle protein can be used to produce glucose.

As we learned before, glycogen stores can be depleted through intense and prolonged exercise, a chronic low carbohydrate diet, or an overall low-energy diet that cannot keep up with the body’s demands.

This is important:

If the body consistently relies on protein for fuel, muscle protein stores will begin to decrease along with lean body mass, which can be detrimental to performance.

This highlights the importance of fully replenishing glycogen stores after intense workouts, as well as on a daily basis.

Consuming carbohydrates (either in liquid or solid forms) is proven to enhance endurance exercise performance.

In this article, we look at how carbohydrates improve exercise performance, reduce muscle breakdown and help to preserve immune function.

How Carbohydrates Improve Exercise Performance

During prolonged exercise your body starts to breakdown muscle and liver glycogen stores. We need this both to fuel your working muscles and to maintain normal blood glucose levels.

As exercise continues, the levels of muscle and liver glycogen deplete. And as glycogen depletion proceeds, this reduces carbohydrate oxidation, increases levels of fatigue and impairs endurance exercise performance (Coyle et al., 1986).

Interestingly, research indicates that brain glycogen levels also deplete following prolonged endurance exercise. And this may be a factor in the central fatigue mechanisms that inhibit exercise performance (Matsui et al., 2011).

The good news is… we can protect against this by consuming carbs, directly before, and during exercise.

Carbohydrates preserve glycogen levels and delay fatigue

Ingesting carbohydrates during exercise has several benefits for endurance athletes:

• Preserves valuable muscle and liver glycogen levels,
• Delays the point of fatigue,
• Protects against low blood sugar levels (hypoglycaemia)
• Improves endurance exercise performance (Coggan and Coyle, 1988; Coyle et al., 1986).

A meta-analysis (Temesi et al., 2011) identified that consuming 30-80g of carbohydrates (6-8% solution) increases time trial performance (~2%) and time to exhaustion (~15%).

How many carbs should you consume during endurance exercise?

• Current research indicates that we should consume around 30-80g/hour of carbohydrate (6-8% solution) to increase endurance exercise in events of > 1 hour (Temesi et al., 2011; Rodriguez et al., 2009; Sawka et al., 2007).

• This becomes increasingly significant as exercise duration increases. And is especially important during events lasting 2 or more hours.
• In practical terms, this means consuming 2-3 energy gels/hour during endurance events lasting longer than 60minutes.

• It’s important to remember that if you’re using energy gels and energy drinks, then you must account for the carbs in both the gels and the energy drink. My advice would be that if your using energy gels, then hydrate with water rather than using energy drinks.

For this to be effective, we should use it with an effective carbo-loading strategy.

Other benefits of carbohydrates during exercise

Besides the performance benefits, there are other reasons why carbohydrates are beneficial during training and competition.

Carbohydrates and immune health

It’s accepted that endurance events — like marathons, triathlons, duathlons, and cycling events — place a significant amount of stress on the immune system. This increases the risk of illness — particularly upper respiratory tract infections. And after prolonged events like ultra-marathons, ironman competitions, your risk of illness can increase significantly.

By ingesting carbohydrates, you reduce the level of stress placed on your immune system. Helping to reduce your risk of infection and improving your general health and wellbeing.

Why does endurance exercise affect immune health?

This is mainly because of the way it lowers blood sugar levels. When blood sugar levels drop, your brain responds by increasing the levels of two key hormones:

Whilst these two hormones play a role in maintaining blood sugar levels, they can have negative effects on immune function. Especially when levels remain elevated for prolonged periods.

When we experience elevated cortisol for sustained periods, it can have a negative effect on immune health, by lowering the numbers of lymphocytes — very important white blood cells that fight invading pathogens.

We can protect against this by maintaining blood sugar levels during endurance training and competitions.

Carbohydrate and protein breakdown during aerobic exercise

Another problem associated with endurance exercise is muscle damage:

1. Muscle membranes can become damaged
2. Individual muscle cells can become damaged and break down
3. We also break muscle proteins down for use as energy within aerobic metabolism.

Importantly, the level of muscle breakdown increases when blood sugar levels drop and cortisol levels rise.

How does cortisol affect muscle breakdown?

First, levels of cortisol become elevated during periods of glycogen depletion and when blood sugar levels are low. This increase in cortisol helps to preserve muscle glycogen stores and maintain blood sugar levels.

Second, cortisol achieves this by increasing the availability of fatty acids and amino acids, for aerobic metabolism.

With amino acids, cortisol increases muscle catabolism (muscle breakdown). And this increases the amount of amino acids in the blood, which we can then use these during aerobic metabolism.

As mentioned, we can reduce the negative effects of cortisol by consuming carbohydrates to help maintain blood glucose levels, during prolonged endurance events and training.

How to improve endurance, protect the immune system and reduce muscle breakdown

Endurance athletes competing in events of >1hours duration can enhance endurance exercise performance, preserve immune function, and reduce muscle breakdown, by ingesting either energy gels or a carbohydrate energy drink:

Energy gels: aim to consume 2-3 energy gels per hour during prolonged endurance events. We should use these in combination with adequate hydration.

Energy drinks: consume ~500-600ml/hour of energy drink containing ~6% carbohydrate solution.

Carbohydrates during longer training sessions:

Consuming carbohydrates during longer endurance training sessions can help to reduce muscle breakdown. And may help to maintain normal immune function.

That said, sometimes it’s beneficial to train in a fasted state:

Why limit carbohydrate ingestion during aerobic training?

As we’ve discovered, carbohydrates can enhance exercise performance, reduce muscle breakdown and preserve immune function.

Despite the obvious benefits, sometimes we choose not to consume carbohydrates during training.

So why is that?… Simply put, this may diminish some benefits of aerobic training, and in particular fat metabolism.

This relates to how consuming carbohydrates increases carbohydrate metabolism. And this may compromise the training benefits of long endurance training sessions, where the primary aim is to develop muscular endurance, efficiency and fat metabolism.

• The ingestion of carbohydrates can have a significant effect on exercise performance
• During prolonged or intense exercise, the body breaks down and depletes muscle glycogen stores. Eventually this reaches a point of reduced carbohydrate availability. And may negatively affect fat metabolism, increase rates of fatigue, and increase muscle protein breakdown.
• By ingestion carbohydrates, we can maintain blood sugar levels, preserve muscle and liver glycogen stores, reduce muscle breakdown, lower cortisol levels, maintain immune function and enhance exercise performance
• Current research suggests that athletes should consume 30-80g carbohydrate/hour. This can either be in a 6-8% solution, or consumed as gels.
• This is beneficial in events of >1hour, but especially during events of 2 hours or more.

References

Acevado, E.O. and Goldfarb, A.H. (1989). Increased training intensity effects on plasma lactate, ventilatory thresholds, and endurance. Medicine and Science in Sports and Exercise. 21, 563-568.

Costill, D.L. (1986). Inside Running: Basics of Sports Physiology. Benchmark Press: Indinapolis, USA.

Coyle, E.F., Feltner, M.E., Kautz, S., Hamilton, M.T., Montain, S.J., Baylor, A.M., Abraham, L.D. and Petrek, G.W. (1991). Physiological and biochemical factors associated with elite endurance cycling performance. Medicine and Science in Sports and Exercise. 23, 93-107.

Fallowfield, J.L. and Wilkinson, J.L. (1999). Improving sports performance in Middle and Long-Distance Running. Chichester: John Wiley and Sons, LTD.

Jones, A.M. (1998). A five year physiological case study of an Olympic runner. British Journal of Sports Medicine. 32, 39-43.

Londeree, B.R. (1997). Effect of training on lactate/ventilatory thresholds: a meta analysis. Medicine and Science in Sports and Exercise. 29, 837-843.

Martin, D.E. and Coe, P.N. (1997). Better Training for Distance Runners (2nd edition). Human Kinetics: Champaign, IL, USA.

Neumann, G., Pfutzner, A. and Berbalk, A. (2000). Successful Endurance Training. Oxford: Meyer and Meyer Sport (UK), LTD.

Noakes, T.D. (1991). Lore of Running. Human Kinetics: Champaign, IL, USA.

Pate, R.R. and Branch, J.D. (1992). Training for endurance sport. Medicine and Science in Sports and Exercise. 24, S340-343.

References:

Coggan A. R., and Coyle E. F. (1988) Effect of carbohydrate feedings during high-intensity exercise. J. Appl. Physiol. 65:1703–1709.

Coyle E. F., Coggan A. R., Hemmert M. K., Ivy J. L. (1986) Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. J. Appl. Physiol. 61:165–172.

Matsui T, Soya S, Okamoto M, Ichitani Y, Kawanaka K, Soya H. (2011) Brain glycogen decreases during prolonged exercise. J Physiol. 2011 Jul 1;589(Pt 13):3383-93. Epub 2011 Apr 26.

Rodriguez NR, Di Marco NM, Langley S (2009) American College of Sports Medicine position stand. Nutrition and athletic performance. Med Sci Sports Exerc. 2009;41:709–31.

Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS (2007) American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39:377–90.

Temesi J, Johnson NA, Raymond J, Burdon CA, O’Connor HT. (2011) Carbohydrate ingestion during endurance exercise improves performance in adults. J Nutr. 2011 May;141(5):890-7. Epub 2011 Mar 16.

Related pages: