Sports Nutrition – ATP – Metabolism

Sports Nutrition pertains to everything we put into our bodies which contribute to the fuel supply our body uses for activity.  How well we understand the role nutrients play has a direct correlation to the efficiency of the body. The body converts food into fuel. It does so using different energy pathways.

ATP – What is it ATP and its mechanism of action?

  • ATP is energy in the form of adenosine triphosphate.
  • Energy is released by the breakdown of ATP. It is that which allow the contraction of muscle cells.
  • Each nutrient has unique properties that determine how it gets converted to ATP.
  • Carbohydrates fuel exercise of a moderate to high intensity
  • Fat can fuel prolonged,  low-intensity exercise.

What are the Energy Pathways?

The body does not easily store ATP. What is stored will generally be used up within seconds, therefore one must create ATP during exercise. The  intensity and duration of the exercise determines which energy pathway is used by the body.

  • Aerobic metabolism (with oxygen)
  • Glycolysis – Anaerobic metabolism (without oxygen)

ATP-CP is the Anaerobic Energy Pathway

  • Sometimes referred to as the phosphate system.
  • It supplies approximately 10 seconds of energy in short bursts of exercise.
  • Does not require any oxygen to create ATP
  • The anaerobic energy pathway starts off by using any ATP that is stored in the muscle. Within 2-3 seconds, this ATP is used.
  • Following that it uses creatine phosphate to resynthesize ATP until the CP runs out. This accounts for another 7 seconds.
  • Once the ATP and CP in the body is used up the body then moves on to utilising aerobic or anaerobic metabolism to continue creating ATP to fuel exercise.

Anaerobic Metabolism – Glycolysis

  • Glycolysis, creates ATP from carbohydrates.
  • Lactic acid is a by-product of glycolysis.
  • Offers energy from a partial breakdown of glucose
  • No need for oxygen
  • Produces energy for short, high-intensity exercise lasting no more than a few minutes.

Aerobic Metabolism

  • Aerobic metabolism fuels the energy needed for long duration activity.
  • Uses oxygen to convert nutrients (carbohydrates, fats, and protein) to ATP
  • Slower at conversion of ATP as it relies on the circulatory system to transport oxygen to the working muscles first before creating ATP.
  • Aerobic metabolism is used primarily during endurance exercise.
  • Endurance exercise is less intense and continues for longer periods.
  • During exercise an athlete will move through these metabolic pathways.
  • As exercise begins, ATP is produced through anaerobic metabolism.
  • With an increase in breathing and heart rate, there is more oxygen available initiating aerobic metabolism
  • This will continue until reaching lactate threshold
  • If this level is passed, the body does not have the capability to deliver oxygen fast enough for generation of ATP
  • Anaerobic metabolism resumes.

Fueling Energy Systems Effectively

  • Nutrients get converted to ATP based upon the intensity and duration of activity
  • Carbohydrate is the main nutrient fueling exercise of a moderate to high intensity
  • Fat is a great fuel for endurance exercise but is not sufficient for high intensity requirements i.e.) sprinting.
  • Exercising at low intensity one will have enough fat storage to fuel training for several hours so long as there is sufficient oxygen to allow for fat metabolism.
  • Increased exercise intensity initiates carbohydrate metabolism to resume. More efficient than fat metabolism, it has a limit on energy stores.
  • Stored carbohydrate is referred to as glycogen
  • When glycogen depletion occurs (stored carbohydrates are used up) fatigue may set in
  • An athlete can continue moderate to high intensity exercise for longer simply replenishing carbohydrate stores during exercise.
  • It is highly suggested to consume easily digestible carbohydrates during prolonged moderate training
  • Without adequate carbohydrates intensity must be reduced to source fuel from fat metabolism
  • Increased intensity results in the halt of carbohydrate metabolism efficiency
  • Anaerobic metabolism resumes due to the fact that the body is incapable of receiving and distributing oxygen at a quick enough pace for fat or carbohydrate metabolism.
  • Carbohydrates have the ability of producing nearly 20 times more energy (in the form of ATP) per gram so long as it is metabolised with adequate oxygen.
  • With continued training, these energy systems adapt becoming more efficient. This will allow for more prolonged exercise duration at higher intensities.

What is REE

REE – Resting energy expenditure—the amount of calories one uses when the body is at rest.

The pituitary gland, stimulates the thyroid gland to secrete hormones which will influence the rate that tissues burn nutrients to produce energy.


If you are a woman:

A woman’s appetite is aligned with her menstrual cycle. Its fluctuation parallels with her REE, which is raised just before or at the onset of ovulation. A woman’s appetite is highest at menstruation falling sharply soon after that.

If you are a man:

Men make lots of testosterone and this makes satisfying one’s nutritional needs much easier. The average male REE is approx 10 percent higher than the average women. Therefore, he can consume 10% more calories without gaining weight.

The oxidative system and ATP

This is our primary source of ATP at rest and during longer duration physical activity. Understanding this energy system can help increase performance in endurance training.

Consuming Calories to fuel the Oxidative System

The oxidative system is also known as the Krebs cycle.

  • Carbohydrates = primary source of energy
  • Fats = primary energy sources that are converted into ATP
  • This process occurs in the mitochondria of the cell.
  • Protein is typically not utilised during this energy system
  • Protein may be used during bouts of exercise more than ninety minutes
  • Endurance training must have enough carbohydrate and fat calories for energy.

Exercise for Weight Loss

Low caloric consumption coupled with prolonged exercise may utilise protein to fuel activity. The human body’s greatest source of protein is within the muscle tissue. Without adequate calories of fuel to sustain prolonged exercise, one runs the risk of burning up muscle tissue for energy. This is called gluconeogenesis.


Risk of Weight Gain

Undereating or over-exercising can lead to weight gain. By consuming low calories, one can decrease their thyroid hormone T3 by up to 66%. At this stage, the body will go into energy conservation mode. Weight loss then becomes tough. Assuring the body has adequate fat and carbohydrates will prevent this from occurring.

Carbohydrates and Fats

When at rest fat storage contributes to 70% of one’s fuel requirements and carbs approx 30%. Increased intensity shifts the body to using more carbohydrates for fuel. Prolonged activity (more than three mins) the body uses fats as the primary source of energy. The amount of oxygen present in the blood will key for this transition.

Oxygen in the blood

When there adequate oxygen present in the blood, pyruvate, the end product of glycolysis, can be then transported to the mitochondria. This is an entrance into the oxidative energy system.

Six molecules of NAHD  + two molecules of FADH2. are transported through the electron transport chain and used to convert ADP into ATP. This process is known as oxidative phosphorylation. It yields approx 38 ATP out of one molecule of glucose. This is a much higher energy yield than the other two energy systems.

Free fatty acids can be broken down into acetyl-CoA and hydrogen.
The acetyl-CoA enters the Krebs cycle and the hydrogen atoms are transported through the electron transport chain where ATP is then produced. A limiting factor of all this is oxygen uptake.

  • Oxygen uptake is a person’s ability to take in and use oxygen.
  • The beginning of all activity is anaerobic (without oxygen).
  • This is approx. 3 minutes of training
  • After three mins we are at an oxygen deficit.
  • We need to replenish the oxygen debt.
  • When the oxygen deficit becomes too high, our body continues to utilise anaerobic energy
  • Blood lactate concentrations are then raised and can cause fatigue.
  • Training for prolonged periods helps the body build an aerobic base.
  • This strengthens the oxidative system by increasing one’s VO2 max
  • The V02 max is one’s ability to utilise the oxygen we take in.
  • Interval training helps us recover by raising our body’s ability to lower blood lactate levels. It also assists in making us more efficient at replenishing oxygen debt.