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 brief period, whereas running at a low intensity, as in gentle jogging, means that an athlete can sustain activity for an extended period. There is a relationship between exercise intensity and the energy source.

Energy Pathways

Matthews (1971)^[2] divides 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. The cells can perform work only from the energy released by this compound's breakdown. The breakdown of ATP produces energy and ADP.
CP - Creatine Phosphate: a chemical compound stored in the 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.

When working at 95% effort, these energy pathways are time-limited, and the consensus on these times is as follows:

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. Actively contracting muscles obtain ATP from glucose stored in the bloodstream 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 on the individual, the effort applied, or the rate at which energy is used.

Davis et al. (2000)^[3] show how the energy systems contribute to producing ATP when exercising at 100% effort. The thresholds (T) indicate that the energy system is exhausted - training will improve threshold times.

The Alactic Energy System

Adenosine Triphosphate (ATP) stored in the muscle last for approximately 2 seconds. The resynthesis of ATP from Creatine Phosphate (CP) will continue until CP stores in the muscles 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 a 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.

Energy Production

(Phosphocreatine + ADP) ⇒ (Creatine Phosphokinase) ⇒ (Creatine + ATP).

Influence of the recovery time

The length of recovery between repetitions is vital in recovering power output through CP's resynthesis. A study by Holmyard et al. (1994)^[4] with a group of subjects who performed six-second sprints with recovery intervals from 15 to 180 seconds found that there is an 81% recovery in peak power output (PPO) with a one-minute recovery and a 92% recovery of PPO in three 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 Lactate Energy 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 lactate and hydrogen ions production. The accumulation of hydrogen ions is the limiting factor causing fatigue from 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 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 150m	150 to 300m	300 to 600m
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 1200m	300 to 1200m	300 to 1200m
Example	3 × (60, 80, 100)	2 × 150m + 2 × 200m	3 × 500m

Anaerobic Capacity and Anaerobic Power

Anaerobic Capacity refers to the body's ability to regenerate ATP using the glycolytic system, and Anaerobic Power refers to the body's ability to regenerate ATP using the phosphagen system. These energy systems can be developed with appropriate interval training sessions.

Glycolytic and Phosphagen energy systems

Glycolytic - the breakdown of glucose by enzymes into pyruvic and lactic acids with the release of energy (ATP).

Phosphagen - the use of creatine phosphate stored in the muscles to generate energy (ATP).

Energy Production

(Glucose + 2 ATP) ⇒ (Pyruvic Acid) ⇒ (Lactic Acid + 2 ATP).

Recovery time

Denadal & Higino (2004)^[5] concluded from their research that 8 minutes is all you should take during track speed workouts over anything up to 800 metres - even those going deep into lactate build-up.

The Aerobic Energy System

The aerobic energy system utilises proteins, fats, and carbohydrates (glycogen) to synthesise 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 usual 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 in the removal and turnover of lactate and the body's ability to tolerate higher levels of lactate.
Intensive Tempo - continuous runs at 80 to 90% of maximum heart rate. Lactate levels become high as these runs border on speed endurance and special endurance. Intensive tempo training provides 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 Production

(Glucose + Fats + Amino Acids + Oxygen) ⇒ (Krebs Cycle) ⇒ (34 ATP).

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 approximates the percentage contribution of the energy pathways in certain sports (Fox 1993)^[1].

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

Other names used for the Energy Systems

The Alactic Energy System is also referred to as the:

PCr Energy System.
ATP-CP Energy System.
ATP-PCr Energy System.
Start-Up Energy System.
Creatine Phosphate Energy System.
Oxidative Independent Energy System.
Alactic Anaerobic Energy System.
Short-Term Energy System.

The Lactate Energy System is also referred to as the:

Lactic Acid Energy System.
Lactic Anaerobic Energy System.
Anaerobic Lactate Energy System.
Linking Energy System.
Oxidative Independent Glycolytic Energy System.
Non-oxidative Glycolytic Energy System.
Medium Term Energy System.

The Aerobic Energy System is also referred to as the:

Keep going Energy System.
Oxidative Dependent Energy System.
Long-Term Energy System.

References

FOX, E.L. et al. (1993) The Physiological Basis for Exercise and Sport. 5th ed. Madison: Brown & Benchmark
MATTHEWS, D. et al. (1971) The Physiological Basis of Physical Education and Athletics. Philadelphia: Saunders
DAVIS, B. et al. (2000) The Interrelationship of the energy system and their threshold points [Diagram]. In: Physical Education and the Study of Sport. London: Harcourt Publishers p.139
HOLMYARD, D.J. et al. (1994) Effect of recovery on performance during multiple treadmill sprints. London: E&FN Spon
DENADAL, B.S and HIGINO, W.P. (2004) Effect of the passive recovery period on the lactate minimum speed in sprinters and endurance runners. J Sci Med Sport, 7 (4), p. 488-96

Page Reference

If you quote information from this page in your work, then the reference for this page is:

MACKENZIE, B. (1998) Energy Pathways [WWW] Available from: https://www.brianmac.co.uk/energy.htm [Accessed 14/8/2025]

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