The Glycolytic System
TL; DR:
1) The glycolytic system functions in absence of oxygen and breaks down glucose (sugar) in order to provide energy to working muscle.
2) It is capable of supplying sustained energy for medium-to-high intensity exercise lasting between approximately 30 seconds to 2 minutes.
3) Common exercises which harness the glycolytic system include weight training and medium length sprints and/or interval training.
4) Noxious biproducts produced during glycolysis ultimately inhibit the active muscle from continuing to exercise (metabolic stress).
5) The glycolytic system compliments the phosphagen system before ultimately feeding the oxidative (aerobic) system.
The glycolytic system is most synonymous with weight training for the average reader. Referencing back to the “metabolic stress” topic from previous blogs, the glycolytic system is the formal name of the energy system that is primarily responsible for the accumulation of metabolites that causes the burn and ultimately contributes to repetition-induced mechanical tension.
Much like the phosphagen system, the glycolytic system is extremely beneficial to weight training as it functions primarily in the absence of oxygen. While all of the aforementioned systems work on a continuum of energy contribution during exercise, the phosphagen and glycolytic systems can be thought of as the first two responding systems depending on the length and intensity of the exercise being performed. While the phosphagen system is responsible for the highest effort exercises (think explosive power movements or maximal strength), the glycolytic system is responsible for carrying the majority of the energy producing burden for bouts lasting slightly longer than the 10 seconds of maximal exertion provided by the phosphagen system. Usually, the burn sensation starts to kick in around the 8-10 second mark but it can be sustained for approximately two minutes of high intensity effort (note: slightly less high intensity than the capabilities of the phosphagen system).
The term glycolytic means the breakdown of sugar, specifically, glucose. Where the phosphagen system cycles readily available pools of ATP / ADP / phosphocreatine to provide immediate energy, the glycolytic system is comparatively delayed as it functions on a slightly longer biochemical pathway. The breakdown of glucose has two methods of contributing energy to the exercising body – fast and slow glycolysis. Fast glycolysis is still slower than the production speed of the phosphagen system, but it’s also much faster than waiting around for the oxidative (aerobic) system to kick in via slow glycolysis. The cycling of ADP back into ATP during the phosphagen system is a one-step chemical process whereas complete (slow) glycolysis is a ten-step process. Fast glycolysis provides a quick delivery of two usable ATP molecules at step seven of the slow glycolysis process.
Once the ten-steps of slow glycolysis finishes, the products of the complete breakdown of a glucose molecule ultimately end up being metabolised further in the oxidative system after an approximate two-minute ramp-up time is complete. This two-pronged breakdown of the sugars found in our muscle allow for a nearly immediate supply of ATP to compliment the phosphagen system via fast glycolysis before ultimately being the supplier of sustained energy production after the products of slow glycolysis enter the oxidative metabolism system.
Glycolysis offers strengths and weaknesses. Much like the phosphagen system, fast glycolysis has to pay for its speed of energy production by the accumulation of noxious biproducts which ultimately inhibit the working muscle from continuing to exercise. In order to have a slightly longer energy production lifespan, the intensity of exercise that the glycolytic system can sustain will be less than that of the phosphagen system as well. That said, when taken to completion, slow glycolysis generates the precursor molecules that eventually enter oxidative metabolic pathways and generate a nearly unending (low intensity exercise) amount of ATP. While this intermediate energy system is capable of providing both (nearly) immediate energy and/or the substrates to generate sustained energy – ultimately, the intensity of exercise dictates which of the three systems dominates.
Next, we tie everything together via the oxidative system.
Best,
Eric