The human body utilizes 3 major energy systems to perform work: the phosphagen system, the glycolytic system, and the oxidative (aerobic) system. You must understand that none of these systems operate independently from one another. When you are running a marathon the primary system is oxidative, but all systems are being used to some degree. On the other hand, olympic lifters rely primarily on the phosphagen system, but recruit the glycolytic and aerobic pathways as well. Our energy systems exist on a spectrum known as the “Bioenergetic Continuum”. A well-developed athlete is efficient at accessing all these systems when training and racing.

lifting-300x2191. Phosphagen System: 0-10 second bouts (89-100% of maximal power)
The phosphagen system meets the demands of very intense exercise. It is anaerobic, which means it occurs without oxygen. Any exercise lasting between 0 – 13 seconds is heavily dependent upon this system. This system relies on creatine phosphate for ATP (energy) production and produces energy more rapidly than any other system. Football, high jump, pole vaulting, olympic lifting, 25-meter swimming, and 100-meter running are examples of activities that depend on the phosphagen system.

Since the demand is very high, so is the risk of injury. Anyone attempting this type of training should be structurally sound and warmed up. Exercise should be performed at 89-100% of maximal effort and recoveries should last between 1:00 and 1:20 between.

The following are examples of training protocols that develop the phosphagen system:

  • 10-13 second bouts of sprinting. 1:00-1:20 recoveries.
  • 10-second hill repeats on a bike. Again, the recovery must be adequate.
  • 10-second maximal efforts dispersed throughout a series of easy 200’s in the pool.
  • Resistance training or olympic lifts that require maximal efforts followed by long periods of relief.

imagesCA3AEH0L2. Glycolysis: 30 second-3 minute efforts

There are two types of glycolysis: Fast glycolysis (75-90% of maximal power) and slow glycolysis (30-75% of maximal power). Here, we will combine them for the sake of simplicity.
Glycolytic reactions depend upon carbohydrate (glucose in the blood, and glycogen in the liver/muscle tissue) to produce energy. Glycolysis is the pathway responsible for exercise lasting between approximately 30 seconds and 3 minutes. Fast glycolysis occurs without oxygen (anaerobic). It meets the demands of intense exercise lasting between 30 seconds and 2 minutes.

During fast glycolysis the body uses glucose and glycogen to convert pyruvate into lactic acid for the production of energy. The production of lactic acid makes the process unsustainable. Over time the production out paces the body’s ability to clear lactic acid and its byproducts (hydrogen ions). Eventually the production of hydrogen ions interferes with the muscles ability to function properly.

Slow glycolysis occurs at a slightly lower intensity, typically exercise lasting between 2 and 3 minutes. During moderate bouts of exercise oxygen is available in sufficient quantities inside the cell. When oxygen is available a shift towards the use of slow glycolysis as the primary pathway occurs. Instead of converting pyruvate into lactic acid, slow glycolytic reactions transport pyruvate into the cell’s mitochondria for use in the oxidative system.

Having a well-developed glycolytic system allows an individual to clear lactic acid and blood lactate more quickly, enabling them to exercise at higher intensities for longer periods of time. Work-to-rest ratios should be in the range of 1:1-1:3.

The following are some examples of glycolytic protocols:

  • Running: 4-6 sets of 2-minute bouts (repetitions) of high-intensity running at 75-100% of maximal effort. The periods of relief should last between 4 and 6 min. The number of sets and the length of recovery should correspond to your level of conditioning.
  • Bike Intervals: (across any type of terrain) 4-8 sets of 1-1.5 minutes at 80-95% of a maximal effort. Recovery should be 3-4 min of easy spinning.
  • Resistance training: Any continuous sets or circuits that last for 1-3 minutes. The work to rest ratio should last 1:1-1:3.

untitled23. Oxidative/Aerobic System: exercise lasting 3minutes or longer 

The aerobic/oxidative system is the dominant subsystem for exercise performed at lower intensities. This system is expansive, and sustains activity lasting between 3 minutes and several hours at efforts between 20-70% of maximal capacity. The oxidative system is dependent upon carbohydrates and fats as energy substrates. Utilization of fats, proteins and carbohydrates depends on the intensity and duration of exercise. Generally, as intensity increases, the reliance upon carbohydrates (glucose and glycogen) increases. During sub maximal and steady state exercise, intensity is lower and less dependent upon carbohydrates for fuel. A shift to reliance on fats and proteins (to a lesser degree) occurs.

An expansive and highly-developed aerobic system is important for most athletes (unless they are exclusively strength and power athletes). In order for an athlete to be well rounded and adaptive they must spend the majority of their time developing their aerobic system. Methods employed in training should be dictated by an individual’s goals. The possibilities are virtually limitless provided you have a level of conditioning that will support the workload.

The following are a few examples of exercises that work the aerobic system:

  • Ironman cycling workout, in the context of a 4-hour ride: add 4 sets of 12-minute efforts at the desired race pace, watt production, or heart rate. Since the intensity is relatively low, the recovery periods can be shorter than those needed for phosphagen and glycolytic protocols.
  • Marathoner or half marathoner: In the context of a 60-90 min run add 4 sets of 6-10 minute repetitions at a pace 10-15% higher than desired race pace. Periods of recovery could last between 4 and 10 minutes. Recovery is dependent upon many factors.
  • A swimmer preparing for an open water mile swim: During a 3 mile training swim add between 4 and 6 sets of 400 meters at race pace. Recovery could be 200 meters at a pace 35-40% slower than race pace. 

Fitness will expand with the application of any sound conditioning methods, followed by adequate periods of relief. Remember, no single system is ever used exclusively. The intensity and duration of exercise are the key determinants of which system will be the primary contributor to exercise at any given moment. Only use workloads that your structure and physiology will allow. Development requires consistency and time. There are no shortcuts.

“There is no substitute for hard work and sacrifice, never was, never will be.”
-Lance Armstrong.

Feel free to contact me for further discussion.

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