What are the most misunderstood aspects of energy system development in team sports?

Six leading experts in energy system development were asked this question. This is what they had to say:

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From my experience, the most common misunderstanding when is comes to energy system development is the assumption that the primary focus for performance should be on increasing exercise capacity. In team sports, such as football, the ability of a player to express their full capacity is most often controlled by the tactical, technical and cognitive constraints of the game. Each player has their own physioloigical ‘ceiling’, such as aerobic capacity, RSA, or Max Speed, but it is the game that dictates how close to that ceiling they can operate / express, which must be considered. A good example is max speed, which is rarely ever attaned during a match, because the game doesn’t permit it. That’s not to say maximising a players capacity isnt important, or that the player couldn’t achieve a top speed if required, but the context of the game controlled it. But unfortunetly, too often a player or team is judged on their ability to express their full capacity during a match or training, and if they don’t attain a certain level are often blamed on lack of ‘athletisism’ or ‘attitude’. Context of match situations must be considered in both performance interpretation and session design. 

I won’t mention the team, but a good anecdote I have is that a sport science team analysed the flow of physical output in a match and noticed a spike in sprint volume whenever they scored. For them this was great, the message was simple, sprint more, work harder, and you are more likely to score. And they ran with this. It was only later when they looked depper into video footage did they realise that the ‘Sprint Exposure’ wasn’t coming from the lead up to the goal, but what the team were doing after… sprinting in celebration. Context is everything.

Another misconception is our over-reliance on external loads and it’s impact on the physiological and conditioning outcomes of a session. From an exercise physiology perspective, individual internal responses to training are huge, especially in female athletes. Various factors including hormonal phase, sleep quality, heat, travel, fatigue, and even minor illness can impact the physiological cost of the same drill by upto 15–25%. Session design, match outputs, and external loading are important, but understanding an athletes internal response and their physiological state going into a session must be considered. Ignoring this leads to poorly timed exposures and inconsistent training outcomes. Managing a squad of 30 players individually is challenging, but subjective montoring, screening, and session individualisation needs to be incorpated into daily processes to maximise player development and knowing when you can push.

In football, GPS and our tendency to over-emphasise external load metrics have facilitated this misunderstanding. In training, high-speed running and sprint efforts are often treated as key indicators of physical development, yet they tell us little about the athlete’s actual metabolic cost of the session. Two players can hit identical HSR outputs while experiencing entirely different internal loads and movement efficiencies. Relying on GPS without context regularly skews training decisions. Even with all the technology and data we have today, there are still enviroments where a ‘good performance’ is judged by a players’ absolute Total Distance or High Speed Running Volumes, which is something we must move away from. Movement efficiency and positioning remain undervalued. Players who anticipate earlier, position intelligently, and move economically incur far lower metabolic cost but are often perceived as ‘not working hard’.

Going to my previous point on emphasising the importance of physical capacity and testing, if the constraints of the game don’t elicit an evnirovment to achieve those levels, or a player has the tactical nuence to conserve, then why do we judge them in training or a match for not ‘working hard enough’. Context is key.  We overvalue “fitness” and match outputs, and undervalue how much energy is wasted through inefficient movement, slow recognition, or disjointed team structures. No amount of conditioning compensates for poor tactical and technical behaviours, which is why the best players appear both “fitter” and “smarter”. Their efficient. Some of the highest total distance outputs and HSR values I have seen in opponenets often come from the most disorganised teams / player. 

Another misunderstanding is the separation of energy systems. Team sports never operate in tidy physiological zones. Intensive and extensive days are useful methods of periodisation, but their purpose is to organise total stress (mechanical, metabolic, and cognitive) rather than to target solely isolated physiological pathways. It is ok to have hydrid training sessions whereby different energy systems or session constraints are targeted on the same day. 

Finally, conditioning is still too often viewed as something added on, instead of something that naturally occurs from the game model. The most effective physical development comes from tactical drills and principles that inherently create the required metabolic demand. Actions such as pressing, regains, defensive organisation, spacing, and transitions, it’s the volume and quality of these movements that create the necessary ‘conditioning’. Standalone conditioning blocks are only necessary when the football work has failed to expose athletes to the full spectrum of physical demands in a session or when the session must be more efficient.

In summary, effective energy system development is less about increasing capacity and far more about ensuring players can consistently use that capacity within the technical, tactical, and cognitive realities of the game.

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Most coaches still see ‘energy systems’ as the main driver of high intensity work in team sports. However, for efforts shorter than about 60 seconds, this view fails. These bouts are not ‘alactic, then lactic, then aerobic’. They are instead limited by the fraction of the athlete’s anaerobic speed / power reserve that they use, on top of clear mechanical and neural ceilings.

Hill, ^[1] had already realised this almost a century ago from world record data. He concluded that “performances below 50 seconds are limited by mechanical and neural factors”, which aligns with the current view that very short, maximal efforts are not primarily constrained by metabolism.

Weyand and Bundle, ^[2] confirmed this idea experimentally. In their model, performances of 10–150 seconds could be predicted from maximal anaerobic and maximal aerobic power treated as a shared finite reserve.^[3]

Even very short sprints use some oxygen, but for a single 3–6 s sprint, the main limit is mechanical and neural output, not ATP depletion. ‘Training the ATP reserve’ as a separate target does not make physiological sense.

For longer high intensity efforts (~1–3 min), time to exhaustion at 90–140% vVO₂max is highly variable when intensity is expressed as %vVO₂max but becomes predictable when speed is scaled between critical velocity and maximal sprint speed.^[4] Building on this, ASR/APR is also an important factor.^[5–8]

In team sports, balancing training priorities is key. For single sprints and very short actions, the main priorities are strength, maximal sprint speed, stiffness, force application, and technique.

When it comes to players’ ability to repeat high intensity efforts, I challenge the idea that everyone MUST do extra metabolic conditioning. Instead, if additional conditioning is used, the content and format must be chosen carefully so that the stimulus drives the intended adaptations without overloading players or breaking them.

Remember that improved VO₂max and overall aerobic capacity generally matter, since they drive recovery between efforts (Glaister, 2005).^[9]

Many players already accumulate large volumes of ‘metabolic’ conditioning through regular team training and competition (e.g., small-sided games, two matches per week), often exceeding the suggested minimal exercise dose.^[10]

In these situations, increasing the reserve itself, rather than only trying to ‘train metabolism’, means targeted work on strength and speed can yield larger gains in repeat-effort capacity, with lower relative load per repetition; and, in turn, less fatigue.^[5,6,8]

For substitutes or developing players who do need extra work, improving VO₂max in a team sport context relies on high intensity interval training (HIIT) as the only realistic and efficient option.

HIIT is time efficient, targets both central and peripheral factors, suits explosive player profiles, and can be integrated into game-based drills.^[11]

In contrast, lower-intensity Zone 2 training is hard to fit into congested schedules, has very limited (if any) central effects, and there is essentially no evidence for peripheral changes at current exercise doses.^[11–13]

In fact, it may even slow players down or increase overuse problems.^[14]

Before sending players to ‘work on their metabolism’ through attempts to increase an imagined ‘ATP reserve’ or through long, slow runs, it is worth questioning both the purpose and the methods. Opt for those that widen the speed and power reserves and truly improve recovery between efforts.

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Practitioners tend to put a lot more priority on achieving specific external loading criteria when designing sessions, or rely on specific drills when performing top-ups post game. In both cases, they neglect the athlete’s internal loading.

External load is obviously important, but internal loading (HR response, peripheral blood flow, muscular contraction intensity etc) unlocks more flexibility to drive conditioning without being constrained by traditional external metrics.

The other side of the coin is knowing what aspects of an athlete’s energy system are limiting them. 

Regularly implemented submaximal fitness tests can offer insights into peripheral (peak and average HR) and central (HR recovery) aerobic qualities at a low external load and time cost. When you pair this with maximal muscle function tests (maximal sprints, CODs, CMJs etc), you can begin to build a more holistic profile of and athlete’s strengths and limitations. 

For example, consider a typical MD-3 high load session. The athletes have achieved your planned loading metrics of m/min, and high- and sprint speed running. 

From an external loading point of view, the session is done, and for well conditioned athletes it very well can be. But for others, targeted internal loading strategies offer more conditioning benefits without risking acute loading spikes. 

To develop aerobic capacity, longer duration work with sustained submaximal HR and lower muscular contraction intensity can support athletes with central and peripheral aerobic limitations. Continuous jogging can build lower leg tissue capacity if progressed appropriately, while intermittent submaximal tempo runs can help reinforce efficient mechanics – especially in fast twitch athletes who may suffer technical breakdowns during continuous running. 

Low intensity technical circuits with suitable work:rest ratios to maintain HR at submaximal levels has the added benefit of combining the above adaptations with skill work and muscular contractions more specific to game play.

For aerobic power, accumulating time at ≥90% max HR using higher contraction intensity targets similar aerobic adaptations but can drive greater mitochondrial improvements. 

While traditionally prescribed as linear or shuttle-based intervals, creating longer duration high intensity technical drills and constraining them with small spaces and a variety of movements can create significant internal stress without overloading specific tissues or metabolite build up via appropriate work:rest ratios.

Adjusting those methods toward short (<30s), maximal efforts with incomplete recovery can enhance buffering capacity for athletes who are aerobically solid but struggle with repeatability. Reducing technical actions and providing more space allows quality high intensity efforts and metabolite build up while still managing total external load.

All of these same principles also apply to off-feet conditioning, with the caveat that peripheral adaptations that transfer to on-field performance will be lower.

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Energy system development is often mistakenly attributed to isolated conditioning drills (e.g., traditional running-based HIIT) rather than the cumulative effect of the entire training programme. A single 10–15-minute conditioning drill within the microcycle is unlikely to meaningfully influence overall aerobic capacity. Instead, adaptations result from how different drills interact across multiple sessions, informed by the demands of the sport and the needs of the individual athlete.

The complexity of energy system development encompasses the broader training process, including technical–tactical work, game-based drills, and match exposure. This does not negate the value of targeted running-based conditioning but does emphasise the importance of planning and integrating them within the overall training programme.

Most team-sport conditioning programmes, particularly during the preseason, implemented some form of HIIT, prescribed using an anchor or threshold such as maximal aerobic speed (MAS).

This anchor is fundamental to the prescription process. It determines the relative intensity at which the athlete is typically required to train – at a fraction of MAS – which, in some cases is combined with other outcomes such as maximal speed.

How we quantify MAS therefore has direct implications for the physiological stimulus imposed during training.

There are, however, multiple approaches to define MAS. Time- or distance-based field trials are efficient to implement, yet they do not always capture similar physiological determinants assessed under controlled laboratory conditions.

Incremental tests to exhaustion produce MAS in laboratory testing. The greatest physiological stress in these tests occurs during the final stage(s) of the protocol as speed progressively increases.

In contrast, field-based time trials require athletes to sustain a high, relatively constant intensity for ~6 minutes. Their output is strongly influenced by familiarity, pacing, and tolerance of discomfort.

Practitioners need to be aware of these differences when programming based on these anchors. Then, during training, they have to verify that the intended training intensity elicits the desired internal response, rather than assuming equivalence across methods.

Equating energy system development with exposure to external load metrics such as total or high-speed running distance are often misinterpreted as evidence of improved physiological capacity.

However, these metrics primarily describe what the athlete did, not how the athlete responded.

Without objective indicators of physiological response, external load metrics provide limited insight into whether a given stimulus is producing the intended adaptation. Examining the relationship between external and internal load (e.g., training efficiency indices), alongside regularly monitoring physiological responses to submaximal exercises or drills, leads to better understanding of training effects and, therefore, better decision making.

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Rugby union is a brutal ballet of chaos—intermittent bursts of high-intensity running, accelerations, decelerations, and bonejarring collisions, all interspersed with brief, incomplete recoveries. Players cover between 4,500 and 7,500 metres per game, depending on position, but distance alone masks the true demands. Forwards are favoured for firepower in attritional gain line battles and providing the platforms of attack anddefence, whilst backs provide the mobility to find space and exploit it. The game is not defined by how far players run, but by how often they are forced to produce and reproduce high-intensity efforts under fatigue.

These demands place simultaneous stress on both aerobic and anaerobic systems, requiring athletes to sustain high outputs repeatedly across 80 minutes. Yet despite this, energy system development in rugby is often misunderstood. Too frequently, conditioning is driven by volumetric outputs—distance covered, total running load—rather than the interplay of intensity, effort type, and recovery that truly defines performance.
A key element often overlooked in this discussion is repeated high-intensity efforts (RHIE).

RHIE are typically defined as three or more high-intensity actions within 21 seconds. These actions include running ≥4.4 m/s, accelerations ≥2 m/s², decelerations ≤−2 m/s², or collisions ≥4g. In elite rugby union, these sequences are not random—they cluster around decisive moments: line breaks, defensive stands, and transitions.

Research suggests players complete approximately 11 ± 6 RHIE bouts per match, with around 4 ± 1 efforts per bout. Positional demands shape these outputs. Back-row players tend to accumulate the highest number of efforts due to their hybrid role, while forwards engage in more collision-dominant bouts and backs rely more heavily on running-based efforts.

At higher levels of competition, these demands intensify. Tier 1 competitions show increases in both RHIE frequency (6.5 ± 1.4 vs 5.7 ± 1.5) and efforts per bout (3.0 ± 1.1 vs 2.4 ± 1.2), alongside a greater proportion of collision-based actions—particularly for positions such as hookers and locks.
In other words, as the standard rises, the game becomes less about accumulating volume and more about sustaining repeated, high-intensity outputs under constrained recovery. This is expected with the rise in players’technical ability, team coaching and system cohesion.
Energy system development directly shapes this capacity.

Highly trained athletes do not simply improve through physiological adaptation alone—they become more efficient. Technical improvements in tackling, movement mechanics, and pattern recognition reduce unnecessary energy expenditure. However, efficiency has limits. Running and acceleration efforts may decay in intensity over time, dropping below key thresholds when fatigue sets in. Collisions, however, do not afford this luxury. There is no submaximal tackle at the elite level—intent must remain maximal, or the outcome fails.

This is where RHIE becomes critical. It is not just the presence of high-intensity actions, but their sequencing—mixed efforts performed under fatigue—that drives the metabolic and performance demands of the game. The density of sustained passages creates the bottleneck wherein fatigue becomes apparent.

The major misconception, then, lies in how players are conditioned to meet this reality of punch for counter punch demands. Many programs continue to prioritise high-volume, low-intensity or submaximal work in an attempt to replicate game demands. Yet in more competitive matches, the opposite trend is observed: total distance often decreases, while effort density increases. Contests for territory and gain-line dominance produce more accelerations, more collisions, and less recovery—often within windows shorter than 21 seconds. Despitethis, training frequently fails to reflect these constraints. Steady-state conditioning and high-repetition drills build general endurance, but they do not adequately prepare athletes for the anaerobic demands of repeated high-intensity sequences. As a result, players are conditioned for volume, but not for the moments that decide games.
A more aligned approach is to develop RHIE-specific capacity.

This means structuring training around short clusters of maximal or near-maximal efforts, combining accelerations, decelerations, and collisions, with deliberately constrained recovery periods. The goal is not simply to accumulate work, but to replicate the density and variability of game demands. In doing so, athletes develop the ability to sustain performance when it matters most—not just across the full match, but within the critical passages that define it.

Energy systems in rugby are not about how much work a player can complete in total. They are about how often they can deliver decisive actions under pressure. Misalign training with that reality, and players will endure the game—but fail in its most important moments.

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Personally, I think a lot of what we interpret as metabolic development is often the by product of improved mechanics. Improve the mechanical qualities that drive the game and the metabolic engine frequently improves with them.

Whether it is a conversation about pre season planning, a reflection after a poor performance or an analysis of GPS reports, the discussion often becomes heavily “physiological”. Aerobic capacity, anaerobic systems, lactate tolerance, high intensity running loads… The logic sounds clean enough. Target the right metabolic pathways and players will sustain the demands of the game better.

But in intermittent sports like rugby or football, the physiological cost of the game is heavily shaped by mechanical outputs. Sprinting, accelerating, braking, re accelerating, getting off the floor repeatedly when fatigue starts changing movement strategies.

Two players can perform the exact same drill or game sequence and experience very different physiological stress.

The difference is not always aerobic fitness. In my experience, it is often mechanical. Acceleration ability, eccentric braking strength, sprint mechanics, stiffness qualities, or simply the ability to reproduce force efficiently under fatigue.

When those qualities are limited, movement becomes mechanically inefficient. Ground contact times increase slightly, force is applied less effectively and more motor units must be recruited to achieve the same external task. In simple terms, the same action becomes metabolically expensive.

You can often almost see it late in sessions. One athlete still moves relatively cleanly while another starts fighting the ground a little bit more every rep.

This is probably one of the reasons exposure to high speed running and maximal sprinting appears so closely linked to the readiness of team sport athletes. Sprinting is not only a performance quality. It is also a powerful organiser of coordination, stiffness regulation and force application. Over time, improvements in these qualities tend to reduce the energetic cost of producing game actions.

The same applies to strength and power development. Improvements in maximal force and rate of force development allow athletes to reach required velocities or changes of direction with shorter ground contact times and lower relative effort. The game becomes slightly less costly physiologically because the athlete owns bigger mechanical reserves.

None of this means metabolic conditioning is irrelevant. Team sports clearly rely on well developed aerobic and anaerobic capacities to support repeated high intensity efforts. But when energy systems become the sole focus, I sometimes think we end up chasing symptoms rather than causes.

Perhaps the most useful way to think about energy system development in team sports is not as isolated physiological training, but as an emergent property of the mechanical demands athletes repeatedly encounter in training and competition.