Concurrent Training: Definition, Science & How to Program It

Building Strength and Endurance Together, in One Program

Concurrent training is the simultaneous development of strength and endurance inside a single training program. Instead of cycling between blocks where you build one quality and lose the other, concurrent training trains both at once, so a soldier can lift heavy on Monday, run fast on Wednesday, and ruck long on Saturday without trading off one capability for another. It's the physiological foundation behind every serious tactical fitness program, including the structured periodization built into the Combat Fitness ONE tactical training programs.

The term itself comes out of exercise physiology rather than out of the gym, which is why it turns up in coursework and coaching certifications more often than on a whiteboard. Anyone combining resistance work and aerobic work in the same program is doing concurrent training, whether that's a soldier, a Hyrox competitor, a cyclist adding a squat day, or a lifter who wants to be able to run three miles. What follows is the definition, what the research actually shows about the interference effect, and the principles that separate concurrent training that works from concurrent training that stalls.

• Strength

• Endurance

The two physical qualities concurrent training develops are the same two that almost every operational job demands together, and almost every fitness program treats as opposites. It’s widely used in:

• Military training

• Law enforcement programs

• Firefighter conditioning

• Hybrid athletic systems

• General performance training

What these settings share is a refusal to specialize: the soldier, officer, or firefighter is paid to be capable across multiple physical domains on demand, which is exactly what concurrent training is designed to deliver.

While the concept sounds simple, concurrent training only works under careful planning. Combine strength and endurance work in the wrong sequence or the wrong dose, and progress stalls on both, you get weaker than a dedicated lifter and slower than a dedicated runner. Combine them correctly, with strategic sequencing and periodized intensity, and you produce capable, durable athletes who carry both qualities into the field at the same time.

The difference between those two outcomes is almost entirely programming. For a deeper breakdown of how structured concurrent programs are selected and compared, see this hybrid training program buying guide. Many tactical organizations also compare structured programming against traditional group models, which is explored in the Combat Fitness training app vs unit PT comparison.

What Concurrent Training Actually Means

The clearest definition of concurrent training is this:

The simultaneous development of strength and endurance within the same training program.

That single sentence is doing a lot of work. "Simultaneous" means the two qualities aren't being trained in alternating blocks, they're being progressed in the same week, sometimes in the same session. "Within the same training program" means the volume, intensity, and recovery for both are planned as one system, not bolted together from two. The qualities concurrent training is built to develop include:

• Force production

• Aerobic capacity

• Work capacity

• Fatigue resistance

• Durability

The reason this approach exists is that every tactical environment, military operations, law enforcement patrol, fireground work, demands these qualities together, on the same day, under fatigue. A program that trains them in isolation produces athletes who are only ready half the time.

Why Concurrent Training Exists in the First Place

Most real-world performance settings don't pay you for one quality in isolation. The bodybuilder gets paid for size. The marathoner gets paid for sustained pace. The tactical athlete, the first responder, and the hybrid competitor get paid for everything at once, and they get paid on the worst day, not the best. Two environments illustrate this directly:

Tactical environments

Operators must:

• Carry heavy equipment

• Move long distances

• Perform repeated high-effort tasks

• Recover quickly between efforts

None of those tasks are optional and none of them happen one at a time, which is why training one quality in isolation prepares an operator for none of them.

Hybrid athletic environments

Athletes may need to:

• Lift heavy weights

• Run or cycle long distances

• Perform repeated conditioning efforts

• Maintain strength and endurance year-round

These environments require both:

• Strength

• Endurance

At the same time.

Specialist programming can't deliver that combination, a pure strength block leaves you slow, a pure endurance block leaves you weak, and rotating between the two means you're always behind on whichever you just stopped training. This overlap in demands is also what defines broader hybrid training systems.

The Interference Effect: Concurrent Training's Central Problem

Any honest discussion of concurrent training has to start with its central problem, the interference effect. The interference effect is the phenomenon where adding endurance training to a strength program reduces the size and speed of strength adaptations, and vice versa. It's not a marketing term and it's not contested at the level of whether it exists; the debate is over how big it is and how to manage it. The mechanism is covered in full in the interference effect explain, which outlines how competing adaptations impact performance.

The interference effect breaks down into three connected observations:

• Strength training and endurance training trigger different adaptations.

• When performed incorrectly, they can compete for recovery resources.

• This competition may reduce strength or power gains.

This is what early concurrent training research, Hickson's 1980 study being the most cited, actually found. Athletes who layered high volumes of endurance work onto a strength program saw measurable shortfalls:

• Smaller strength increases

• Reduced power development

• Greater fatigue

The proposed mechanism is worth understanding, because it explains why how you arrange the work matters more than whether you do it at all. Resistance training signals for growth largely through the mTOR pathway. Endurance training signals for aerobic adaptation largely through AMPK, which is activated when cellular energy runs low. Those two pathways are partly antagonistic: AMPK activation can blunt mTOR signalling, which is the molecular version of "cardio interferes with lifting." The important caveat is that this signalling effect is acute and short-lived, measured in hours, while strength and muscle are built over months. Which is exactly why the practical answer to interference is spacing and dosing rather than avoidance.

But the research has matured significantly since then. Recent work, particularly studies on periodized concurrent programming and zone 2 aerobic conditioning, points the other direction:

• Proper scheduling reduces interference.

• Low-intensity aerobic work has minimal negative impact on strength.

• Periodized concurrent training produces strong results across multiple qualities.

Those three claims are worth attaching to specific work, because "the research says" is exactly the phrase that should make you ask which research.

Wilson and colleagues (2012) ran the meta-analysis that reframed the question. Rather than asking whether interference happens, they showed it scales with the frequency, duration and modality of the endurance work, which turned a yes-or-no argument into a dosing one. Murach and Bagley (2016) reviewed the hypertrophy evidence and found no whole-muscle size difference between concurrent training and resistance training alone. Coffey and Hawley (2017) described the competing molecular signalling directly. Petré and colleagues (2021) extended the analysis across untrained, moderately trained and trained populations, and Schumann and colleagues (2022) concluded that concurrent training does not compromise hypertrophy or maximal strength, with one specific exception: explosive strength gains are attenuated, particularly when both qualities are trained in the same session.

That exception is the practically useful finding. The picture that emerges from twenty years of follow-up work is not that Hickson was wrong, it's that his result was a dose effect at the high end. Maximal strength and muscle size hold up well under concurrent training. Rate of force development, the explosive quality, is the one that pays, and it pays most when the sessions collide. The conclusion is straightforward: the issue isn't concurrent training itself. It's poorly structured concurrent training. A structured approach to managing this is outlined in concurrent training frameworks.

How to Structure Concurrent Training (Without Triggering Interference)

The detailed week-by-week mechanics of structuring concurrent training belong in a programming guide, that's what our framework post is for. At the level of principles, though, every effective concurrent program rests on the same three pillars:

1. Primary and secondary training goals

At any given time:

• One quality is emphasized.

• Others are maintained.

For example:

Strength-focused phase

• Strength is primary.

• Endurance is supportive.

Endurance-focused phase

• Endurance is primary.

• Strength is maintained.

This prevents all qualities from competing at once. This is the single biggest mistake new concurrent athletes make: trying to peak everything at once, then wondering why nothing moves. Pick one, maintain the rest.

2. Strategic session sequencing

The order of training matters more than most athletes realize, strength work after a hard run and a hard run after heavy lifting produce very different adaptation outcomes from the same total weekly volume. Common sequencing approaches include:

• Strength before endurance in the same session

• Separating sessions by several hours

• Alternating high-intensity and low-intensity days

• Pairing heavy lifting with low-intensity aerobic work

The pattern across all four is the same: protect the quality you're prioritizing this phase from the residual fatigue of the quality you're maintaining.

The evidence behind the first bullet is reasonably consistent. Craig and colleagues (1991) found that running before lifting reduced lower-body strength gains while leaving upper body unaffected, and later reviews of intra-session sequencing have generally favored resistance work first when lower-body strength is the priority. The mechanism is unglamorous: whichever quality goes second is trained by an athlete who is already tired.

Separation matters as much as order. If both qualities land on the same day, put more hours between them than feels necessary, and if the schedule won't allow it, keep one of the two easy. Two hard sessions stacked back to back is the specific arrangement the interference research keeps identifying as the problem.

The one thing worth being honest about is modality, because the literature genuinely disagrees. Lundberg and colleagues (2022) reported interference as more pronounced with running than cycling, which fits the eccentric-loading explanation most coaches give. Sabag and colleagues (2018) reported the opposite, with cycling producing the larger negative effect on lower-body outcomes. Anyone telling you this is settled is telling you more than the evidence supports. The practical position is to pick the modality that matches the job or the event, manage the total load, and stop optimizing a variable the researchers can't yet agree on.

3. Volume and intensity control

The third pillar is the one most concurrent athletes underestimate: you cannot run maximally, lift maximally, and condition maximally inside the same week. Something has to be dialed back, and the dial is volume and intensity. Concurrent athletes have a hard ceiling on all three of these:

• Lift maximally

• Run maximally

• Perform intense conditioning

All at the same time.

Effective concurrent programs respect that ceiling by managing the four levers below:

• Limit high-intensity endurance sessions

• Use zone 2 aerobic work as the base

• Control total weekly volume

• Rotate stress across systems

This helps prevent excessive fatigue. The result is a training week with high total work but controlled peak stress, which is exactly what allows multiple qualities to progress at once. These approaches are often contrasted with traditional models in our concurrent vs block periodization.

"Control total weekly volume" is easier to agree with than to act on, so it's worth putting rough ceilings on it. Guidance circulating in this space generally puts total weekly aerobic work somewhere in the three-to-six hour range for a strength-prioritizing athlete, with running specifically capped lower, around two to three hours, because of its higher mechanical cost. High-intensity interval work is the most expensive item on the list and the most tempting to add; one genuinely hard session a week is usually enough alongside a strength emphasis, and two is the point at which most athletes start reporting the failure signs listed further down.

Progress volume slowly, in the region of ten percent a week rather than in jumps, and deload every three to six weeks by cutting volume rather than intensity. The deload is not optional. It is the mechanism by which accumulated fatigue clears so that the adaptations you've been driving all block can actually appear.

The Role of Zone 2 Aerobic Base Work

The single most important, and most skipped, piece of concurrent training is low-intensity aerobic development, typically programmed as zone 2 work at roughly 60–70% of max heart rate. The reason zone 2 sits at the foundation of every serious concurrent program is that it's the only form of cardio that builds endurance without burning down the recovery budget you need for strength gains. Zone 2 work:

• Improves recovery between strength sets

• Supports long-duration performance

• Reduces injury risk

• Builds endurance without excessive fatigue

This is also the cardio modality least associated with the interference effect in the research literature, long, slow, controlled aerobic work and heavy strength work appear to coexist far better than high-intensity intervals and heavy strength work do. Build the aerobic base first; layer faster work on top once the base is established.

The Benefits of Concurrent Training for Tactical Athletes

When structured properly, concurrent training produces:

• Balanced strength and endurance

• Improved work capacity

• Greater fatigue resistance

• Better recovery between efforts

• Increased durability

• Real-world readiness

None of these benefits are exotic, they're exactly the qualities that show up on every operational fitness test and every after-action review of physically demanding jobs.

• Tactical athletes

• Hybrid competitors

• General performance populations

Of those three groups, the tactical athlete benefits most: the job description literally requires capability across multiple physical domains simultaneously, which is the precise problem concurrent training is engineered to solve.

Signs Concurrent Training Is Working

You’ll typically see:

• Gradual strength improvements

• Better endurance over time

• Consistent weekly training

• Improved recovery between sessions

• Fewer injuries

Progress may be slower in any single domain, but overall performance improves steadily. That slower-but-steady pattern is the signature of a working concurrent program, and it's also why athletes coming from specialist backgrounds (pure powerlifting, pure running) often misread it as a plateau and bail out early.

Signs Concurrent Training Is Failing

Poorly structured concurrent programs often lead to:

• Plateaued strength

• Stagnant conditioning

• Chronic fatigue

• Joint or tendon pain

• Inconsistent training weeks

These problems usually come from:

• Too much intensity

• Poor session sequencing

• Lack of a primary focus

• Excessive total volume

All four root causes trace back to the same underlying mistake: trying to maximize every quality at once. These issues are especially common in scenarios where endurance training reduces strength, a failure pattern that almost always comes down to dose, not the modality itself. One qualification on that list. Cutting volume resolves the joint and tendon pain that comes from doing too much, and most of it is exactly that. It does not resolve pain with a structural cause, and from the inside the two are not reliably distinguishable. If something is worsening week over week, hurts at rest, or is changing how you move, get it assessed by a qualified professional rather than programming around it.

Concurrent Training vs Hybrid Training

The terms are often used interchangeably, but there is a subtle difference.

Concurrent training

• A scientific term

• Focuses on combining strength and endurance

Hybrid training

• A broader concept

• Includes strength, endurance, work capacity, durability, and adaptability

Concurrent training is essentially the physiological foundation of hybrid training systems, the science of what's happening inside the athlete. Hybrid training is the broader programming philosophy that sits on top of it. You can do concurrent training without calling it hybrid. You cannot build a serious hybrid program without doing concurrent training, whether you call it that or not.

The Bottom Line on Concurrent Training

Concurrent training is the simultaneous development of strength and endurance inside a single training program. It's the physiological mechanism behind every credible tactical fitness system, and it's the reason a structured program will always outperform a stitched-together one. It works best when:

• One quality is prioritized at a time

• Sessions are sequenced intelligently

• Intensity is controlled

• Volume is progressed gradually

Get those four right and the interference effect becomes a managed variable instead of a wall. Get any one of them wrong and progress stalls on both ends. When concurrent training is structured correctly, it produces athletes who are:

• Strong

• Enduring

• Durable

• Operationally ready

That combination, strong, enduring, durable, operationally ready, isn't a marketing tagline. It's the literal performance profile required by every job this site exists to serve. Concurrent training is how you build it.

Common Questions About Concurrent Training

What Is the Definition of Concurrent Training in Exercise Science?

Concurrent training is the simultaneous development of strength and endurance within a single training program, as opposed to developing them in separate sequential blocks. The term originates in exercise physiology and is most closely associated with Hickson's 1980 study, which first documented that adding endurance work to a strength program attenuated strength development.

Does Concurrent Training Really Reduce Strength Gains?

Less than the original research suggested. Later meta-analyses indicate that maximal strength and muscle hypertrophy hold up well under concurrent training when it's programmed sensibly, while explosive strength and rate of force development are the qualities that suffer, especially when both are trained in the same session. The effect scales with how much endurance work you do and how close it sits to lifting.

Should You Lift or Do Cardio First?

Lift first when strength is the priority, which is the more common case. The evidence on intra-session order generally favours resistance work before endurance for lower-body strength outcomes, and upper-body strength appears largely unaffected by order either way. If the two can be separated by several hours or onto different days, that is better than optimizing the order within one session.

What's the Difference Between Concurrent Training and Block Periodization?

Concurrent training develops multiple qualities at once, with one emphasized and the others maintained. Block periodization concentrates on one quality at a time in sequential blocks, accepting that the others detrain somewhat before being rebuilt. Concurrent suits athletes who need year-round readiness across qualities; block periodization suits athletes peaking for a known date.

References

Hickson, R. C. (1980). Interference of strength development by simultaneously training for strength and endurance. European Journal of Applied Physiology and Occupational Physiology, 45(2–3), 255–263.

Craig, B. W., et al. (1991). Effects of running, weightlifting and a combination of both on growth hormone release.

Wilson, J. M., Marin, P. J., Rhea, M. R., Wilson, S. M. C., Loenneke, J. P., & Anderson, J. C. (2012). Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 26(8), 2293–2307.

Murach, K. A., & Bagley, J. R. (2016). Skeletal muscle hypertrophy with concurrent exercise training: contrary evidence for an interference effect. Sports Medicine.

Coffey, V. G., & Hawley, J. A. (2017). Concurrent exercise training: do opposites distract? The Journal of Physiology, 595(9), 2883–2896.

Sabag, A., et al. (2018). The compatibility of concurrent high intensity interval training and resistance training for muscular strength and hypertrophy: a systematic review and meta-analysis.

Petré, H., et al. (2021). Development of maximal dynamic strength during concurrent resistance and endurance training in untrained, moderately trained, and trained individuals: a systematic review and meta-analysis.

Lundberg, T. R., et al. (2022). The effects of concurrent aerobic and strength training on muscle fiber hypertrophy: a systematic review and meta-analysis.

Schumann, M., et al. (2022). Compatibility of concurrent aerobic and strength training for skeletal muscle size and function: an updated systematic review and meta-analysis.