Energy Pathways

Introduction

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 of time. Running at a low intensity, as in gentle jogging, means that an athlete can sustain activity for a long period of time. Training introduces another variable, and the sprinter who uses sound training principles is able to run at a high intensity for longer periods of time. Similarly, the endurance athlete who uses sound training methods can sustain higher intensities during a set period of time. 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-PC 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.
• PC - Phosphate-creatine : a chemical compound stored in muscle, which when broken down aids in the manufacture of ATP. The combination of ADP and PC 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 general consensus is:

The result of muscle contraction produces ADP which when coupled with PC regenerates ATP. PC 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 of time requires the complete oxidation of carbohydrates or free fatty acids in the mitochondria. The carbohydrate store will last approx. 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 5 seconds. This gives us around 5 to 7 seconds of ATP production.

To develop this energy system, sessions of 4 to 7 seconds of high intensity work at near peak velocity are required. e.g.

• 3 * 10 * 30m with recovery of 30 seconds/repetition and 5 minutes/set.
• 15 * 60m with 60 seconds recovery
• 20 * 20m 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 irons. The accumulation of hydrogen irons is the limiting factor causing fatigue in runs of 300m to 800m.

Sessions to develop this energy system:

• 5 to 8 * 300m fast - 45 seconds recovery - until pace significantly slows
• 150m intervals at 400m pace - 20 seconds recovery - until pace significantly slows
• 8 * 300m - 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:

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 50-70% 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 60-80% 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 80-90% 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 basically 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)

Associated Pages

The following Sports Coach pages should be read in conjunction with this page:

• Endurance training
• Energy Expenditure
• Energy Source
• Heart Rate Training Zones
• Lactic Acid

Associated Web Sites

The following web sites contain more information on this topic:

• www.coachr.org

Associated Journals and Books

The following journals and books contain more information on this topic:

• Peak Performance - Issue 72
• Peak Performance - Issue 122 page 7
• Peak Performance - Issue 128 page 10
• Peak Performance - Issue 181 page 1
• The Coach - Issue 6, page 23
• BMC News - Vol Issue 13 - page 6
• Advanced PE for Edexcel - F Galligan et al - page 379
• Physical Education and the study of sport - B Davis et al - page 143
• Fox E L, Bower R W, Foss M L 1993 The physiological basis for exercise and sport

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