Energy Production in The Body

Adenosine Triphosphate (ATP)

Energy Production in The BodyAdenosine Triphosphate is a chemical stored in the muscles that produces energy for muscle contraction to take place.  During rest more ATP is produced than needed and excess energy is transferred to creatine in your muscles. Increased blood flow by hyperemia help produce Creatine Phosphate. The body can store 80g-100g of ATP at one time. ATP is utilized for quick spurts of significantly demanding activities. During more strenuous workouts Adenosine Triphosphate is broken down at an accelerated rate and is depleted quickly.  

ATP + Creatine <–> ADP + Creatine Phosphate

  1.  Muscle activity breaks down ATP and Creatine as Adenosine Diphosphate(ADP) and Creatine Phosphate are created
  2. Creatine Phosphate (CP) aids to replenish Adenosine Diphosphate(ADP)
  3. ADP is then used to replenish Adenosine Triphosphate(ATP)
  4. ATP is used to convert Creatine to Creatine Phosphate

Naturally ATP and CP levels are replenished after a few minutes of rest after anaerobic activity.  CP level deplete within 15 second of physical activity.  The body stores four to six times more Creatine Phosphate than Adenosine Triphosphate, allowing for rapid ATP replenishment.

During aerobic activity the body uses other resources such as carbohydrates and fats from the glucose in your muscles, liver, and blood to make Adenosine Triphosphates.  The increased blood flow produced during muscle contraction optimizes energy usage for both aerobic and anaerobic activities.

Aerobic vs Anaerobic

At rest our body uses aerobic metabolism to fuel our body with energy. As we gradually start to exercise and slowly increase demand we can maintain use of aerobic energy production.

As intensity increases we get to a point where we start feeling fatigue and anaerobic metabolism begins.  At this point lactic acid begins to build up as the body’s energy expenditure increases.  Activities like weightlifting that require quick surges of energy can immediately provoke anaerobic metabolism.


Anaerobic conditioning stimulates your type II fast twitch muscle fibers for improvements in power, strength, and hypertrophy. Through anaerobic resistance training spikes in testosterone, growth hormones, and cortisol are prevalent. Anaerobic status occurs in high intense training with the absence of oxygen. As oxygen depletes lactic acid builds up causing muscle fatigue.

Lactic Acid

Lactic acid is produced as a byproduct of breaking down glycogen (glycolysis) without oxygen.  Mitochondria in the muscles absorb this lactic acid and use it as fuel. During high intensity training lactic acid can build up in the blood faster than the mitochondria can absorb it thus reaching it’s threshold.  This takes place after about 2 minutes of strenuous exercise and is signaled by feeling fatigued. As anaerobic endurance increases so does lactate threshold allowing for a delay in muscle fatigue and an improvement in performance.

2 Anaerobic System Energy Sources

Anaerobic endurance is fueled by levels of Adenosine Triphosphate(ATP), Creatine Phosphate(CP), and Glycogen.

  • The Phosphagen system uses ATP and CP for energy during the first 10-20 seconds of highly intensive activity and restore during a full recovery of 5-7 minutes.

  • The Glycolytic system kicks in after 10-20 seconds and provides energy through the breakdown of glycogen. This energy lasts for a few minutes of intense exercise with short rests.

Anaerobic exercises include weight training, agility training, intense interval training, and plyometrics. High anaerobic conditioning occurs in track and field sprinters, boxers, short distance swimmers, basketball players,fencers, and strength competitors.


Aerobic Energy Production

During strenuous aerobic exercise the muscles demand oxygen for metabolism.  Aerobic activity is supported by carbohydrates, lipids, and amino acids in circulating blood. During muscle contraction blood flow increases, surging oxygen and nutrients to these areas. This blood flow stimulates enzymes in the muscles to synthesize glycogen to glucose as a source of energy.  This is why long distance runners load carbohydrates or take glucose supplements before a race.

Aerobic Energy Usage

Aerobic exercise puts stress on the respiratory system increasing breathing frequency and volume.  This enhances overall blood flow helping muscles sustain during activity and providing them with more oxygen and nutrients. The development of type I slow twitch muscles improve aerobic endurance. Non-demanding movements for extended periods of time like long distance running or swimming are ideal.





Requires Oxygen

Does Not Require Oxygen

Macronutrient Use

Proteins and Fats


Energy Systems

  • Oxidative System
  • Glycolysis
  • Phosphagen System

  • Glycolysis: Phase 1

Cell Location



Macronutrients consist of Proteins, Fats, and Carbohydrates.  These macronutrients contains chemical energy which is converted into usable energy for our body.

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