Energy Pathways
Energy production is both time and intensity related. Running at a very high intensity, as in sprinting, means that an athlete can operate effectively for only a very short period. Running at a low intensity, as in gentle jogging, means that an athlete can sustain activity for a long period. Training introduces another variable, and the sprinter who uses sound training principles is able to run at a high intensity for longer periods. Similarly, the endurance athlete who uses sound training methods can sustain higher intensities during a set period. There is a relationship between the exercise intensity and the energy source.
Energy Pathways
D. Matthews and E. Fox, in their revolutionary book, "The Physiological Basis of Physical Education and Athletics", divided the running requirements of various sports into the following "energy pathways": ATP-CP and LA, LA-02, and 02.
- ATP - Adenosine Triphosphate: a complex chemical compound formed with the energy released from food and stored in all cells, particularly muscles. Only from the energy released by the breakdown of this compound can the cells perform work. The breakdown of ATP produces energy and ADP.
- CP - Creatine Phosphate: a chemical compound stored in muscle, which when broken down aids in the manufacture of ATP. The combination of ADP and CP produces ATP.
- LA - Lactic acid: a fatiguing metabolite of the lactic acid system resulting from the incomplete breakdown of glucose. However Noakes in South Africa has discovered that although excessive lactate production is part of the extreme fatigue process, it is the protons produced at the same time that restrict further performance
- O2 means aerobic running in which ATP is manufactured from food mainly sugar and fat. This system produces ATP copiously and is the prime energy source during endurance activities
These energy pathways are time duration restricted. In other words, once a certain time elapses that specific pathway is no longer used. There is some controversy about these limitations but the consensus is:
| Duration | Classification | Energy Supplied By |
| 1 to 4 seconds | Anaerobic | ATP (in muscles) |
| 4 to 10 seconds | Anaerobic | ATP + CP |
| 10 to 45 seconds | Anaerobic | ATP + CP + Muscle glycogen |
| 45 to 120 seconds | Anaerobic, Lactic | Muscle glycogen |
| 120 to 240 seconds | Aerobic + Anaerobic | Muscle glycogen + lactic acid |
| 240 to 600 seconds | Aerobic | Muscle glycogen + fatty acids |
The result of muscle contraction produces ADP which when coupled with CP regenerates ATP. CP is stored in the muscles. Actively contracting muscles obtain ATP from glucose stored in the blood stream and the breakdown of glycogen stored in the muscles. Exercise for longer periods requires the complete oxidation of carbohydrates or free fatty acids in the mitochondria. The carbohydrate store will last approximately 90 minutes and the free fatty store will last several days.
All three energy systems contribute at the start of exercise but the contribution depends upon the individual, the effort applied or on the rate at which energy is used. The following graph depicts how the energy systems contribute to the manufacture of ATP over time when exercising at 100% effort. The thresholds (T) indicate the point at which the energy system is exhausted - training will improve the thresholds times.
The Anaerobic (ATP-CP) Energy System
Adenosine Triphosphate (ATP) stores in the muscle last for approximately 2 seconds and the resynthesis of ATP from Creatine Phosphate (CP) will continue until CP stores are depleted, approximately 4 to 6 seconds. This gives us around 5 to 8 seconds of ATP production.
To develop this energy system, sessions of 4 to 8 seconds of high intensity work at near peak velocity are required e.g.
- 3 × 10 × 30 metres with recovery of 30 seconds/repetition and 3 minutes/set.
- 15 × 60 metres with 60 seconds recovery
- 20 × 20 metres shuttle runs with 45 seconds recovery
Influence of the recovery time
The length of recovery between repetitions is important in the recovery of power output through the resynthesis of CP. A study by Holmyard et al. (1994) with a group of subjects who performed 6 second sprints with recovery intervals from 15 to 180 seconds found that there is a 81% recovery in peak power output (PPO) with a 1 minute recovery and a 92% recovery of PPO in 3 minutes.
| Recovery Time (seconds) |
PPO recovery (%) |
| 15 | 68.7 |
| 30 | 73.6 |
| 45 | 78.1 |
| 60 | 81.0 |
| 120 | 88.2 |
| 180 | 92.2 |
The Anaerobic Lactate (Glycolytic) System
Once the CP stores are depleted the body resorts to stored glucose for ATP. The breakdown of glucose or glycogen in anaerobic conditions results in the production of lactate and hydronium ions. The accumulation of hydronium ions is the limiting factor causing fatigue in runs of 300 metres to 800 metres.
Sessions to develop this energy system:
- 5 to 8 × 300 metres fast - 45 seconds recovery - until pace significantly slows
- 150 metre intervals at 400 metre pace - 20 seconds recovery - until pace significantly slows
- 8 × 300 metres - 3 minutes recovery (lactate recovery training)
There are three different working units within this energy system: Speed Endurance, Special Endurance 1 and Special Endurance 2. Each of these units can be developed as follows:
| Speed Endurance | Special Endurance 1 | Special Endurance 2 | |
| Intensity | 95 to 100% | 90 to 100% | 90 to 100% |
| Distance | 80 to 150 metres | 150 to 300 metres | 300 to 600 metres |
| No of Repetitions/Set | 2 to 5 | 1 to 5 | 1 to 4 |
| No of Sets | 2 to 3 | 1 | 1 |
| Total distance/session | 300 to 1200 metres | 300 to 1200 metres | 300 to 1200 metres |
| Example | 3 × (60, 80, 100) | 2 × 150 metres + 2 × 200 metres |
3 × 500 metres |
The Aerobic Energy System
The aerobic energy system utilises proteins, fats and carbohydrate (glycogen) for resynthesising ATP. This energy system can be developed with various intensity (Tempo) runs. The types of Tempo runs are:
- Continuous Tempo - long slow runs at 50 to 70% of maximum heart rate. This places demands on muscle and liver glycogen. The normal response by the system is to enhance muscle and liver glycogen storage capacities and glycolytic activity associated with these processes.
- Extensive Tempo - continuous runs at 60 to 80% of maximum heart rate. This places demands on the system to cope with lactate production. Running at this level assists the removal and turnover of lactate and body's ability to tolerate greater levels of lactate.
- Intensive Tempo - continuous runs at 80 to 90% of maximum heart rate. Lactate levels become high as these runs boarder on speed endurance and special endurance. Intensive tempo training lays the base for the development of anaerobic energy systems.
Sessions to develop this energy system:
- 4 to 6 × 2 to 5 minute runs - 2 to 5 minutes recovery
- 20 × 200m - 30 seconds recovery
- 10 × 400m - 60 to 90 seconds recovery
- 5 to 10 kilometre runs
Energy System recruitment
Although all energy systems turn on at the same time the recruitment of an alternative system occurs when the current energy system is almost depleted.
The following table provides an approximation of the percentage contribution of the energy pathways in certain sports. (Fox et al. 1993)
| Sport | ATP-CP and LA | LA-O2 | O2 |
| Basketball | 60 | 20 | 20 |
| Fencing | 90 | 10 | |
| Field events | 90 | 10 | |
| Golf swing | 95 | 5 | |
| Gymnastics | 80 | 15 | 5 |
| Hockey | 50 | 20 | 30 |
| Distance running | 10 | 20 | 70 |
| Rowing | 20 | 30 | 50 |
| Skiing | 33 | 33 | 33 |
| Soccer | 50 | 20 | 30 |
| Sprints | 90 | 10 | |
| Swimming 1.5km | 10 | 20 | 70 |
| Tennis | 70 | 20 | 10 |
| Volleyball | 80 | 5 | 15 |
Table adapted from Fox E. L. et al, The Physiological Basis for Exercise and Sport, 1993
Associated Pages
The following Sports Coach pages should be read in conjunction with this page: