A GUIDE TO TRAINING THE THREE ENERGY SYSTEMS FOR SOLDIERS AND OPERATORS

How the ATP-PC, glycolytic and aerobic systems power tactical performance - and how to train each one without neglecting the others.

Introduction

Every physical task is paid for by one of three energy systems. A sprint to cover, a fire position held under load, a twenty-mile tab: each draws on a different fuel pathway, and each responds to different training. Learn how they work and you can train each one on purpose instead of by accident.

Their performance, endurance, and resilience rely heavily on how well their bodies can produce and use energy.

This article aims to provide a comprehensive guide to the three main energy systems, what they're used for, how they interact, and how to train each one inside a tactical-athlete programme.

Where does energy come from?

The human body is a complex machine that requires daily energy intake to function, especially in high-performance settings like military training or operations.

Energy in the body is predominantly derived from the conversion of food into usable energy forms, primarily Adenosine Triphosphate (ATP). ATP serves as the main 'currency' of energy in biological systems, allowing for the transfer and utilisation of energy within cells.

Sources of energy

The macronutrients carbohydrates, fats, and proteins are the principal sources of energy. Once ingested, these macronutrients are metabolised into glucose, fatty acids, and amino acids, respectively, which are then used to aid in the production of ATP through various pathways.

• Carbohydrates - broken down and converted into glucose, they serve as a rapid source of energy. Glucose is especially important for high-intensity activities and is primarily utilised in the ATP-PC and anaerobic glycolytic systems.

• Fats - metabolised into fatty acids, they are the main source of energy during low-intensity, prolonged activities, like long marches or walk-ins, where the aerobic system is dominant.

• Proteins - while not a primary source of energy, amino acids from protein can be converted into glucose when other sources are unavailable. This is generally inefficient and not the preferred pathway for high-performance activities.

The three energy systems

Depending on the intensity and duration of the activity, different energy systems are activated along a continuum to produce ATP:

• ATP-PC system - utilises stored ATP and creatine phosphate for immediate energy during high-intensity, short-duration tasks.

• Anaerobic glycolytic system - uses glucose and glycogen reserves to produce ATP in the absence of oxygen, best for activities lasting between 30 seconds to 2 minutes.

• Aerobic system - involves the use of oxygen to produce ATP from carbohydrates, fats, and occasionally proteins, suitable for low-to-moderate-intensity activities lasting longer than 2 minutes.

Table 1. The three energy systems summarised - fuel sources, durations, power output, and tactical examples.

The fundamentals of each energy system

ATP-PC system (phosphagen system)

The ATP-PC system is the body's go-to energy system for short, high-intensity bursts of activity, such as a 100-metre sprint or lifting a heavy load. It utilises ATP and creatine phosphate stored in the muscles for immediate energy - this is one of the reasons supplementing with creatine monohydrate will help to improve your power output and performance.

Training approach:

• Exercise structure - high-intensity, short duration (less than 10 seconds).

• Work-to-rest ratio - 1:12 to 1:20.

• Context for military - sprinting with gear, lifting a heavy artillery shell, breaching, casualty pickup.

Anaerobic glycolytic system (lactic acid system)

This system kicks in during sustained, high-intensity activities lasting for up to 2 minutes. It utilises glucose and glycogen but does so in the absence of oxygen, leading to lactic acid production.

Training approach:

• Exercise structure - high-intensity, medium duration (30 seconds to roughly 2 minutes).

• Work-to-rest ratio - 1:3 to 1:5.

• Context for military - climbing a steep hill, fast-roping from a helicopter, sustained sprint-pursuit.

Aerobic system

The aerobic system is the long-term energy system, utilising carbohydrates, fats, and sometimes proteins in the presence of oxygen. This system is the primary source of energy for activities lasting longer than 2 minutes.

Training approach:

• Exercise structure - low-to-moderate intensity, long duration (anything more than 2 minutes).

• Work-to-rest ratio - continuous activity with minimal rest.

• Context for military - long slow marches, tabbing, day-to-day movement, sustained patrolling.

How energy systems interact: a continuum, not isolated boxes

While it's useful to learn about the ATP-PC, anaerobic glycolytic, and aerobic systems separately for the sake of understanding and training, it's crucial to recognise that these systems do not operate in isolation.

Rather, they work simultaneously and synergistically to meet the energy demands of various physical activities at any given time.

The continuum concept

The idea of energy systems operating along a continuum means that no single system works alone at any given moment. As the intensity and duration of an activity change, the dominant energy system may shift, but the others continue to contribute to some extent.

• High-intensity, short duration - although the ATP-PC system predominates, the anaerobic glycolytic and aerobic systems are also at work, providing supplementary energy.

• Moderate intensity, medium duration - in activities lasting up to 2 minutes, the anaerobic glycolytic system may take the lead, but the ATP-PC system still provides an initial burst of energy, and the aerobic system begins to contribute more as time progresses.

• Low intensity, long duration - during prolonged activities, the aerobic system is dominant, yet the ATP-PC and anaerobic glycolytic systems can kick in during brief moments of higher intensity, such as sprinting the last stretch of a long run.

Why this matters for tactical training

Operational tasks rarely sit cleanly inside one energy system. A loaded patrol is dominated by the aerobic system, but the contact, the bound, the casualty drag and the final dash to cover all draw on the glycolytic and phosphagen systems at the moment they're needed. A soldier conditioned only in one system will fail the moment the demand shifts to another.

This is the operational case for training all three systems deliberately rather than relying on whichever one your favourite training mode emphasises.

How to train all three energy systems effectively

Each system responds to a different stimulus. Doing the same hard-feeling sessions repeatedly trains very few of them well. Below is the practical approach for each.

Table 2. Example sessions for each energy system, with work-to-rest ratios and practical session structure.

The 80/20 rule for tactical conditioning

A widely-replicated principle in endurance science is the 80/20 distribution: around 80% of weekly conditioning time should be at low-intensity (predominantly aerobic / Zone 2), with the remaining 20% at high intensity (glycolytic and phosphagen work). This ratio holds for elite endurance athletes (Seiler & Kjerland 2006) and translates well to tactical-athlete contexts where operational tasks are heavily aerobic.

The mistake to avoid is the middle-ground trap - sessions that are too hard to recover from quickly but not hard enough to drive top-end adaptations.

Easy should be easy. Hard should be hard.

The middle ground is where most progress goes to stall.

A sample weekly programme for energy system training

A realistic distribution for a tactical athlete or selection candidate combining strength, energy system development and operational specificity:

Table 3. Sample week distributing energy system work across strength, aerobic volume, lactate threshold, and operational transfer. Easy days are easy. Hard days are hard. No middle-ground sessions.

This is a base-building template. Specific phases (pre-selection, post-injury return, deployment workup) require different distributions - but the principles hold: train all three systems, distribute volume across the week, and respect the 80/20 ratio.

What are the common mistakes in energy system training?

Four errors regularly inhibiting progress for tactical athletes that we see:

1 - Living in the middle ground. Most candidates train almost everything at 'felt hard but not maximal' intensity. This trains no system well. Either keep it conversational (aerobic) or genuinely hard (glycolytic / phosphagen). Pick one per session.

2 - Too much HIIT, not enough Zone 2. Social-media-driven training culture overemphasises high-intensity sessions. They have a place, but only 15-20% of total volume. The aerobic base is the bigger lever for operational performance.

3 - Ignoring the phosphagen system. True maximal power and short-burst capacity matters operationally - sprinting to cover, lifting an injured man, breaching. Short, fully-rested sprints once a week build this without significant fatigue cost.

4 - Treating recovery as a luxury. All three systems require recovery to adapt. Stacking hard sessions without rest produces neither aerobic gains nor power gains - just accumulated fatigue. The 80/20 distribution naturally provides the recovery if it's followed.

Practical applications for military personnel

Understanding this interplay is essential for military training regimes:

• Variable training - incorporate exercises that engage all energy systems, to prepare for unpredictable situations.

• Task-specific training - when preparing for known tasks, focus on the dominant energy system but don't neglect the others.

• Recovery considerations - recognise that energy systems supporting 'background' activity will influence recovery times for the dominant system in use.

Conclusion

For optimal performance in their physically demanding roles, soldiers and operators must understand and train their energy systems effectively.

By targeting the ATP-PC, anaerobic glycolytic, and aerobic systems using appropriate exercises and work-to-rest ratios, military personnel can be better equipped to handle the multifaceted challenges they encounter.

It's important to note that these energy systems do not operate in isolation but along a continuum, adjusting their contributions based on the specific demands of the activity at hand.

Throughout our training, we prioritise a holistic approach that ensures all three energy systems are optimally developed.

By applying these principles and training approaches, soldiers and operators can maximise their physical capabilities, thereby enhancing both their effectiveness and resilience in the field.

Energy system training for soldiers: frequently asked questions

What are the three energy systems?

The three energy systems are the ATP-PC (phosphagen) system, the anaerobic glycolytic system, and the aerobic (oxidative) system. The ATP-PC system powers explosive, short efforts under 10 seconds. The glycolytic system handles sustained high-intensity work from around 15 seconds up to 2 minutes. The aerobic system supports lower-intensity work lasting longer than 2 minutes. All three operate continuously along a continuum, with the dominant system shifting as activity duration and intensity change.

How do I train my aerobic system?

Through sustained, conversational-pace work - runs, rows, bike rides, hill walks - at around 60-70% of your maximum heart rate. Sessions of 45-90 minutes, three to five times per week, build the central cardiovascular adaptations (stroke volume, mitochondrial density, capillarisation) that underpin all endurance and operational performance. Around 80% of total weekly conditioning time should sit here for most tactical athletes.

How do I train my anaerobic system?

Through high-intensity intervals lasting 30 seconds to 2 minutes with limited rest. Examples: 60-second hill repeats, 400m running intervals, sandbag carries at near-maximal effort. Work-to-rest ratios of 1:3 to 1:5 give the system enough recovery to repeat efforts at meaningful intensity. Two sessions per week is typical; more produces diminishing returns and significant fatigue cost.

What is the ATP-PC system?

The ATP-PC (or phosphagen) system uses stored adenosine triphosphate and creatine phosphate in the muscles for immediate, maximal-power output. It's the system that powers a sprint to cover, a maximal lift, a breach kick, or a casualty pickup. It depletes within around 10-15 seconds of maximal effort and requires several minutes of rest to fully restore. Creatine monohydrate supplementation supports this system directly by increasing creatine phosphate stores.

Why do soldiers need all three energy systems?

Operational tasks rarely sit cleanly within one system. A patrol is aerobic, but the contact, the bound, the casualty drag and the final dash to cover require glycolytic and phosphagen power. A soldier trained only in one system will fail the moment the demand shifts. The full-spectrum athlete handles all three because all three are needed across a single operational cycle.

How long should I train each energy system?

Distribute weekly time roughly 80% aerobic, 15% glycolytic, 5% phosphagen. For a soldier doing 8 hours of conditioning weekly, that's around 6.5 hours easy aerobic work, 1.25 hours of glycolytic intervals, and 15-20 minutes of true ATP-PC work (short sprints, heavy power lifts). The phosphagen percentage is small because the system requires full recovery between efforts - high intensity, low volume.

What energy system does running use?

Depends entirely on intensity and duration. A 50-100m sprint is almost pure phosphagen. A 400m flat-out is glycolytic-dominant. A 1.5 mile test sits at the glycolytic-aerobic boundary. A 5km is heavily aerobic with a glycolytic finishing kick. A long tab is almost entirely aerobic. Training the right system for the test you're preparing for is what "specificity" actually means.

Can I improve all energy systems at once?

Yes, but the rates of improvement vary and concurrent training requires careful programming. Aerobic adaptations show in 4-6 weeks of consistent Zone 2 work. Glycolytic capacity improves in 4-8 weeks of regular interval work. Phosphagen and neural power improve in 6-12 weeks. The mistake is trying to maximally develop all three simultaneously - usually a block-based emphasis (4-8 weeks favouring one system while maintaining the others) produces better results than spreading attention thinly.

What is lactate threshold and how do I train it?

Lactate threshold is roughly the highest intensity you can sustain before blood lactate begins accumulating faster than your body can clear it. It sits at the high end of the aerobic range and the bottom of the glycolytic range - typically around 80-88% of maximum heart rate for trained individuals. Train it with sustained efforts of 6-20 minutes at "comfortably hard" pace, two to three times every two weeks. Improvements show as faster sustainable paces at the same heart rate.

Should I use heart rate or pace to train my energy systems?

Heart rate is the more accurate guide because it accounts for daily variation in fitness, fatigue, hydration, and environmental conditions. A pace that feels easy on a fresh day might push you out of Zone 2 on a tired day; the heart rate tells you the truth. Use pace as a secondary marker once you've calibrated your heart-rate zones. Talk-test is a useful third check - if you can speak full sentences, you're in aerobic territory.

References

Baechle, T. R., & Earle, R. W. (2008). Essentials of Strength Training and Conditioning. NSCA.

McArdle, W. D., Katch, F. I., & Katch, V. L. (2010). Exercise Physiology: Nutrition, Energy, and Human Performance.

Seiler, S., & Kjerland, G. Ø. (2006). Quantifying training intensity distribution in elite endurance athletes: is there evidence for an 'optimal' distribution? Scandinavian Journal of Medicine & Science in Sports, 16(1), 49-56.

Buchheit, M., & Laursen, P. B. (2013). High-intensity interval training, solutions to the programming puzzle. Sports Medicine, 43(5), 313-338.

Beattie, K., Kenny, I. C., Lyons, M., & Carson, B. P. (2014). The effect of strength training on performance in endurance athletes. Sports Medicine, 44(6), 845-865.