Fast glycolysis is also known as anaerobic glycolysis and slow glycolysis is commonly called aerobic glycolysis. These are dictated by the energy demands of the cells.  If there is a rapid or high rate of type II muscle fibers being utilized then fast glycolysis is utilized. If there is a demand for primarily type I muscle fibers and oxygen present then slow glycolysis is utilized.

During resistance training your muscles utilize glycogen as its primary fuel source in the process known as glycolysis. This is when your body converts carbohydrates and breaks it down into glucose, and then it is broken down again to form a molecule known as ATP (Adenosine Triphosphate).  After the ATP is utilized it is broken down into ADP (Adenosine diphosphate), which in turn bonds with creatine phosphate to create another ATP molecule.  ATP production occurs in the mitochondria of the muscle cell.

Aerobic System/ Slow Glycolysis: The aerobic system requires 60 to 80 seconds to produce energy for resynthesizing ATP from ADP + P.  The heart rate and respiratory rate must increase sufficiently to transport the required amount of O2 to the muscle cells, allowing glycogen to break down in the presence of oxygen.  Glycogen is the source of energy used to resynthesize ATP in both the lactic acid and aerobic systems.  The aerobic system, however, breaks down glycogen in the presence of O2, producing little or no lactic acid, which in turn allows the athlete to continue to exercise.

The aerobic system is the primary energy source for events lasting between 2 minutes and 2 to 3 hours.  Prolonged work beyond 2-3 hours may result in the breakdown of fats and proteins to replenish ATP stores as the body’s glycogen supply depletes.

The breakdown of glycogen, fats, or protein produces the by-products carbon dioxide CO2 and water H2O, both of which are eliminated from the body through respiratory and perspiration.

The rate at which athletes can replenish ATP is limited by their aerobic capacity, or the maximum rate at which they can consume oxygen.

Anaerobic System/ Fast Glycolysis: The anaerobic system refers to the ATP-CP system, also called the anaerobic alactic since lactic acid is not produced during it; the phosphagen system and the lactic acid system.

ATP-CP System: Muscles can store only a small amount of ATP, energy depletion occurs rapidly when strenuous activity begins. In response, creatine phosphate (CP) or phosphocreatine, which is also stored in the muscle cell, breaks down into creatine (C) and phosphate (P).  The energy released is used to resynthesize ADP + P into ATP.  We can then transform this once more to ADP + P, causing the release of energy required for muscular contraction.

Due to the fact that CP is stored in limited amounts in the muscle cell, this system can supply energy for 8 to 10 seconds.  It is the chief source of energy for extremely quick and explosive activities, such as 100-meter dash, weightlifting, jumping, and throwing events in track and field, vaulting in gymnastics, and ski jumping.

Restoration of Phosphagen: Through restoration the body recovers and replenishes energy stores to preexercise conditions.  Through its biomechanical means, the body attempts to return to physiological balance (homeostasis), which it has the highest efficiency.  Phosphagen restoration occurs rapidly in first 30 seconds it reaches 70%, and in 3 to 5 minutes it is fully restored to 100%.

Lactic Acid System: For intensive events up to 40 seconds such as 200 / 400 meter sprinting, the ATP–CP system first provides energy, followed by 8 to 10 seconds by the lactic acid system.  The lactic acid system breaks down glycogen stored in the muscle cells and liver, releasing energy to resynthesize ATP from ADP + P.  Due to the absence of O2 during the breakdown of glycogen, a byproduct called lactic acid (LA) forms.  When high intensity work continues for a prolonged period, large quantities of lactic acid accumulate in the muscle causing fatigue, eventually stopping physical activity.

Full restoration of glycogen takes a long time, even days, depending on the type of training and diet.  For intermittent activity, typical strength or interval training, restoration takes 2 hours to restore 40%, 5 hours to restore 55%, and 24 hours for full restoration to 100% percent.

If the activity is continuous, typical of high intensity endurance activities, restoration of glycogen takes much longer: 10 hour to restore 60% and 48 hours to achieve full restoration 100%. For a normal, or carbohydrate rich diet, it takes 12 to 24 hours to replenish the liver glycogen.  During training there could be a LA accumulation in the blood, which has a fatiguing effect on the athlete.  Before returning to a balanced resting state, the body has to remove LA from the systems, however this takes some time to achieve this: 10 minutes to remove 25%, 25 minutes to remove 50%, and 1 hour and 15 minutes to remove 95%.

An athlete can facilitate the normal biological process of LA by performing 15 to 20 minutes of light aerobic activity, as the benefit of movement and sweating will help in the elimination of LA and other metabolic residues.   Fitness level is another element that facilitates restoration of energy stores.  A good aerobic base can reduce the time necessary to replenish glycogen stores.

* Please note that I took much of this information directly from the following two textbooks:

Essentials of Strength & Conditioning, National Strength & Conditioning Association, Thomas R. Baechle, Roger Earle, Second Edition, Human Kinetics, 2000

Strength Training, National Strength & Conditioning Association, Lee E. Brown, Human Kinetics, 2007

Jon Torerk, CSCS

(With the help of some of my college textbooks on this one, most of the material I post are from the top of my head and the little amount of memory that I still have added with a little research to make sure I’m correct.)