IB Sports, exercise and health science A.2.3.2 Phosphagen, Glycolytic, and Oxidative Energy Systems During Exercise Notes

The Three Energy Systems

1. Phosphagen System

1. The Phosphagen System, also known as the ATP-PC System, is the body’s quickest source of ATP production.
2. It utilizes stored ATP and creatine phosphate (PC) to provide immediate energy for very high-intensity activities lasting for a few seconds.

Fuel Source

1. ATP stored in muscles (immediate, limited supply).
2. Creatine phosphate (PC) is used to quickly regenerate ATP from ADP. PC stores are replenished during recovery periods.
3. $$ \text{PCr + ADP} \xrightarrow{\text{creatine kinase}} \text{ATP + Creatine} $$

Recovery Time

1. Full recovery of the phosphagen system takes about 2-5 minutes, allowing creatine phosphate to regenerate.
2. During recovery, a period of low-intensity exercise (e.g., walking or light jogging) helps clear waste products and assist in faster recovery.

Benefits

1. Provides immediate ATP production.
2. Supports very high-intensity efforts, such as sprints, weightlifting, or jumping.
3. No oxygen required (anaerobic).

Limitations

1. Limited capacity: once stored ATP and PC are used up, the system is depleted in under 20 seconds at maximal intensity.
2. Requires long recovery time for the complete restoration of stores, which can take several minutes.

2. Glycolytic System

1. The glycolytic system provides energy for activities lasting from 20 seconds to 2 minutes.
2. It involves the breakdown of glucose or glycogen into pyruvate to produce ATP.

Fuel Source

1. Glucose (from blood or muscle glycogen) is broken down into pyruvate to produce ATP.
2. Since it occurs in the absence of oxygen (anaerobic), the byproduct of this process is lactate.

Recovery Time

1. Partial recovery can occur within 30 minutes to 1 hour, but full recovery may take several hours.
2. Lactate clearance is essential for full recovery. Active recovery (e.g., light jogging) speeds up the removal of lactate from the bloodstream.