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.

Energy Systems

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 5 minutes/set.
  • 15 × 60 metres with 60 seconds recovery
  • 20 × 20 metres shuttle runs with 45 seconds recovery

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 hydrogen ions. The accumulation of hydrogen 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:

Associated Books

The following books provide more information related to this topic:

  • Principles of Anatomy and Physiology, G.J. Tortora et al., ISBN 0 06 046704 5
  • Strength Training Anatomy, F. Delavier, ISBN 0 7360 4185 0
  • Atlas of Skeletal Muscles, R.J. Stone et al., ISBN 0 697 13790 2
  • The Muscle Book, P. Blakey, ISBN 1 873017 00 6
  • Advanced Studies in Physical Education and Sport, P Beashel et al., ISBN 0 17 4482345
  • Physical Education and the Study of Sport, B. Davis et al., ISBN 0 7234 31752
  • Essentials of Exercise Physiology, W.D. McArdle et al., ISBN 0 683 30507 7
  • Physical Education and Sport Studies, D. Roscoe et al., ISBN 1 901424 20 0
  • The World of Sport Examined, P. Beashel et al., ISBN 0 17 438719 9
  • Advanced PE for Edexcel, F. Galligan et al., ISBN 0 435 50643 9
  • Examining Physical Education, K. Bizley, ISBN 0 435 50660 9
  • Sport and PE, K Wesson et al., ISBN 0 340 683821
  • PE for you, J. Honeybourne, ISBN 0 7487 3277 2