written by Scott Keast, Education and Safety Co-ordinator
The human body is a marvelous organism. To power all of the musculature and maintain normal metabolism the body relies on three energy systems:
- The Aerobic System
- The Anaerobic System
- The Adenosine Triphosphate (ATP) / Creatine Phosphate (CP) System
Each has its strengths and weaknesses, but together they form a very sophisticated, overall energy system that can supply the correct amount of fuel and oxygen, via the circulatory system, to all of the body’s individual muscle cells under most conditions. Like any other system in the body we can train and improve these systems to take advantage of them for our cycling.
The Aerobic Energy System
This is the system that the endurance cyclist must train fully in order to spare the anaerobic and ATP/CP energy systems for when they are needed. This is likely one of the most difficult areas to get a cyclist to train because it involves high volumes of moderate paced riding. Training times will vary depending upon the event or tour that is targeted. In general though, a maximum of 3-4 hours of riding at an endurance heart rate or intense endurance heart-rate will be sufficient to create a supercompensation (the body is stimulated to grow stronger after a stimulus) response from the body.
The aerobic system has the following advantages:
- It provides fuel (glucose) to the cells through the synthesis of glycogen, carbohydrate, fat, and protein.
- Synthesis takes place within the presence of oxygen, with the only by-products being CO2 and water.
- Minimal production of lactate and the hydrogen ions that are believed to cause “the burn”.
- Energy production can continue indefinitely, provided the body continues to be well hydrated and fed, and work loads remain low enough that the aerobic system remains the primary energy provider.
The disadvantages of the aerobic system are:
- The system takes several minutes to respond to the loads that are placed on the body.
- The aerobic system requires more than 20 steps to convert glycogen and / or glucose to ATP to fuel the cells.
- The system cannot provide enough fuel to the mitochondria to allow for high intensity workloads.
The Anaerobic Energy System
Once the aerobic system can no longer supply sufficient oxygen to the cells the process of converting glycogen to glucose, then to ATP shortens, but there is a hefty price to pay for this. Fuel resources are used up much more rapidly and hydrogen ions that result from this process serve to limit how long the muscle contraction can continue. The good news is that the system can be trained and the body is better able to buffer the effects of the hydrogen ions. Training to fine tune and improve this system is done by doing interval workouts at or slightly below your anaerobic threshold. By doing intervals the stimulus to the body is sufficient to cause improvement, but not so long as to cause catabolic waste to cause damage to the muscle cells and the need for extensive recovery time.
The advantages of the anaerobic energy system are:
- It is capable of supplying fuel to the cells when there is an oxygen deficit.
- It allows an athlete to maintain high workloads for about an hour to an hour and a half.
- It can respond to high workloads much more quickly than the aerobic system.
The disadvantages of the anaerobic system are:
- Due to the lack of oxygen, glycolysis takes place which is catabolic (destructive) to the muscle cells if the process continues for too long.
- Lactate and hydrogen ions are produced. The lactate is used to continue energy production (current theory), while the hydrogen ions irritate the muscle tissue and chemically limit muscle contraction. This creates the burning sensation and the heavy wooden feeling in the muscles.
- The system cannot supply energy for extended periods. When fully trained, an athlete can sustain sub anaerobic threshold intensities for 1 to 1.5 hours.
- Fuel resources are used up very rapidly and the body cannot synthesize fats and protein quickly enough to supply this system so, glycogen and carbohydrates must be used.
The ATP/CP Energy System
This system is used for quick maximal efforts lasting 10 seconds or less. Situations where this might be used include; sprinting, closing a gap, and attacking on a hill. The reason that this system can provide these bursts of maximum output is because the Adenosine Triphosphate and Creatine Phosphate are stored within the muscle tissue – there is no lengthy chemical breakdown of fuel. The breakdown of ATP by the mitochondria creates energy that the muscle cells can use and the breakdown of the CP actually precipitates the rebuilding of the ATP molecule. Nevertheless this process is very brief.
The advantages of the ATP/CP System are:
- The system has the ability to provide a comparatively brief but intense amount of energy for times when the body must do a large amount of work over a brief period of time (part of our basic fight or flight instinct no doubt).
- Glycolysis is not involved so the process is not catabolic.
- The Creatine Phosphate in a sense “recycles” and rebuilds the ATP molecule to extend both the time that one is able to use this energy system, as well as the number of times that one can use the system.
- The system can and should be trained by doing short maximum intervals with a recovery of three times the work load time.
The disadvantages of the ATP / CP System are:
- It can only provide energy for brief periods of time—eight to ten seconds.
- The system can be accessed a number of times, but will eventually exhaust the “built-in” supply of ATP – even with the help of the Creatine Phosphate molecule.
- Rebuilding of the supply of ATP takes 24 to 48 hours (it is helped through the use of a high glycemic sports drink with the addition of some protein (four grams of carbohydrate to one gram of protein) within the first 1/2 hour following a training ride or event. That first half hour window is crucial – beyond that time re-uptake resumes at a normal pace.
So there you have it – three energy systems which can all be optimized by systematically using them in a controlled manner. The important points to know are:
- Be conscious of what system is being used while out on the bike under various conditions.
- Know how to exploit the benefits and minimize the negative effects of each system.
- Train each system so that it meets your needs for the type of riding you do most, or type of event you are targeting (e.g. don’t over emphasize the ATP / CP System if you do mostly endurance events). and
- Make sure that you include recovery in your training plan. Remember fitness is gained while you rest – exercise is the stimulus.