Concurrent Training: How to Run Strength and Cardio Without Sabotaging Either

A heavily nuanced conversation, but hopefully we will break down some of the mystery of: What the interference effect actually is, the variables that determine its effect size, and the programming framework that lets tactical athletes build more than one quality at once.

Every operator, soldier or tactical athlete has the same problem in some form.

They need to be strong. Operationally strong. Strong enough to carry the casualty, breach the door, deadlift the bergen back onto a lorry, and hold the pull-up bar long enough for full marks in a test.

They also need to be aerobically conditioned. Conditioned enough to tab very long distance, run the test routes, complete the assault course, and keep moving when the deprivation stacks.

And the dominant fitness-industry advice for the last forty years has been that you can't really do both at the same time. That training for strength and training for endurance produce competing adaptations and that you have to pick one. This is what's called the interference effect, and it has been argued about, replicated, refuted, partially confirmed, contextualised, and re-argued continuously since Hickson first identified it in 1980.

The current position is more nuanced - and more useful - than either camp tends to claim.

The interference effect is something real for sure but it is also a lot smaller than most lifters fear, and more manageable than most endurance coaches assume. It depends substantially on modality, volume, intensity, order, recovery, and caloric intake. Programmed sensibly, it's possible to build meaningful strength and meaningful endurance in the same training block - which is exactly what every tactical athlete needs and what most generic programmes fail to deliver.

This article covers what the interference effect actually is at a molecular and practical level, the variables that change its size, the two priority cases (strength-led vs endurance-led), the weekly distribution that minimises interference, and the common mistakes that quietly cost candidates years of progress.

What is concurrent training?

Concurrent training is the simultaneous pursuit of strength and endurance adaptations within the same training programme - typically over weeks and months, not a single session.

Almost every athlete, especially military athletes are, by definition, training concurrently. A soldier preparing for selection is building strength (deadlifts, squats, pull-ups, carries) at the same time as building aerobic capacity (Zone 2 base, VO2 max intervals, loaded marches). A serving operator maintaining readiness is doing the same in lower volumes.

The question is not whether to train concurrently - you need to become a ‘specialist generalist’, so you have to…The question is how to programme it so that both qualities adapt rather than competing.

What is the interference effect?

The interference effect refers to the observation that concurrent strength and endurance training tends to produce smaller strength gains than strength training alone - particularly when endurance volume is high.

The seminal research is Hickson (1980), who showed that adding 6 days per week of endurance training to a strength programme markedly reduced strength gains in previously untrained subjects compared with the strength-only group. Endurance gains were preserved; strength gains were not.

This was for decades the default conclusion: cardio kills your gains - don’t you dare walk up stairs if you’re trying to be big and strong!

The picture has become substantially more nuanced as the research base has matured. Wilson and colleagues (2012) conducted the most-cited meta-analysis of concurrent training, examining 21 studies and finding that the size of interference depended heavily on modality, intensity, frequency, and duration of endurance work - not simply its presence.

The 2022 systematic review by Schumann and colleagues replicated the broad finding with more granular precision. Interference is real and measurable but typically very modest. It scales with endurance volume. It is meaningfully reduced by appropriate programming and volume control. And critically - strength training does not appear to meaningfully interfere with endurance adaptation in the opposite direction.

The molecular mechanism - AMPK versus mTOR

To programme concurrent training from an intelligent standpoint, it helps to understand the molecular signalling that the interference effect comes from.

Two intracellular pathways are central to the adaptation response from training. mTOR (specifically mTORC1) is the protein-synthesis pathway - the signal that drives muscle hypertrophy and strength adaptation. AMPK is the energy-sensing pathway - the signal that drives mitochondrial biogenesis, fat oxidation, and aerobic adaptation.

AMPK activation directly inhibits mTOR. When AMPK is heavily activated - typically by prolonged endurance work, particularly in a depleted state - the protein synthesis signal that drives strength adaptation is blunted for several hours afterwards.

Table 1. The two pathways behind training adaptation and the molecular basis of the interference effect. Understanding this is the foundation of intelligent concurrent programming.

The practical implication: the interference window is biggest in the 6-12 hours after a hard endurance session. Separate hard cardio from hard strength by at least 6 hours where possible, and ideally by 24+ hours when both qualities are at their hardest in the week.

The six variables that determine how much interference you actually get

The interference effect is not a binary switch. It scales with several specific variables, and changing each one changes the size of the interference.

Table 2. The six variables that determine the magnitude of interference in concurrent training. Programming around these reduces interference from a potential 30-40% loss of strength gain to functionally negligible levels.

The practical takeaway: the interference effect is almost always programmable around. Below 3 endurance sessions per week of moderate duration, with strength and cardio appropriately separated, with cycling weighted higher in the cardio modality and adequate calories, the interference is typically 5% or less - a level most tactical athletes will gladly accept for the operational benefit of dual adaptation.

Which goal takes priority? The choice of two camps

The first programming decision is which adaptation is the priority. Most tactical athletes are either strength-led or endurance-led in their current phase. The distribution shifts accordingly.

Table 3. Two strategic distributions for concurrent training, depending on the dominant goal. The strength-priority case applies during base-building phases or post-injury rebuilds. The endurance-priority case applies during selection prep and pre-deployment workups.

Neither distribution sacrifices the other quality - both build strength and endurance. The difference is the bias of the programme. For most tactical athletes, the strategic emphasis shifts across training blocks: 8-12 weeks strength-priority during a base building phase, then 8-12 weeks endurance-priority leading into a course or test.

How should you structure your training week for concurrent work?

A practical weekly distribution for a serving soldier or selection candidate, balanced across strength and endurance:

Table 4. Sample weekly distribution balancing concurrent strength and endurance development. Strength and high-intensity cardio are separated. Easy cardio sits between strength days. Sunday is non-negotiable recovery.

Three principles govern the structure. Hard strength and hard/long cardio should go on different days. Easy cardio (Zone 2) sits between strength days because it produces minimal AMPK activation and supports recovery. The hardest single day in the week is buffered by lower-intensity work either side.

What order do strength and cardio go in the same session?

Some weeks the schedule forces a same-day combination. Here the principle is clear: strength before cardio preserves strength quality. Cardio before strength can meaningfully degrade subsequent lifting performance.

The mechanism is partly glycogen depletion (cardio depletes the substrate the heavy lift needs) and partly central nervous system fatigue (intense cardio dulls the neural drive required for maximal force production). Studies consistently show that lifting after even moderate prior cardio produces lower force output, fewer reps at any given load, and slower bar speeds.

When same-day is unavoidable:

• Strength first. Cardio after.

• Ideally separate by at least 4-6 hours, even within the day (morning strength, evening cardio is the gold standard).

• Eat between the two - protein plus carbs. Replenish substrate and provide amino acids.

• If the cardio is easy Zone 2, the interference is much smaller than if it's intervals.

Modality matters - why cycling is the lowest-interference cardio

Not all cardio creates equal interference, which is why we use different modalities throughout all of our training programmes. Cycling produces less interference with strength than running for several reasons.

First, the biomechanics. Cycling is concentric-dominant and lacks the eccentric loading of running. The muscle damage profile is therefore lower, reducing the recovery cost that interferes with subsequent training.

Second, the muscular recruitment. Cycling and squatting share similar muscle groups but in different patterns, and the carryover is broadly positive - strength from squatting transfers to cycling power. Running and squatting overlap less, with stride patterns and impact loading creating recovery debt that running-only cardio doesn't share.

Third, the metabolic profile. Cycling-induced AMPK activation appears to produce less mTOR inhibition than running-induced activation at equivalent intensities, possibly because of the lower whole-body inflammation response.

Practical implication: if you're in a strength-priority phase and you have flexibility in cardio modality, weight cycling and rowing higher than running. Run when running specificity is needed (selection prep, SCA prep, 1.5-mile improvement). Use cycling for general aerobic maintenance during heavy strength blocks.

What are the common mistakes in concurrent training?

Five easily rectifiable errors consistently undermine concurrent programmes for tactical athletes.

Treating concurrent training as purely additive - For example, just sticking a strength programme on top of an endurance programme without reducing volume on either side produces fatigue without adaptation. Both programmes need to be slightly trimmed volume wise mainly to fit alongside each other.

Same-day cardio before strength. The most common programming error. Cardio before lifting degrades the lifting session. Strength always before cardio in the same session - or separated by 6+ hours.

Too much moderate-intensity cardio. Moderate steady-state cardio (the oft demonised grey zone) is the highest-interference cardio for the smallest aerobic return. Either go easy (Zone 2) or genuinely hard (intervals). Avoid the middle ground when trying to grow both qualities simultaneously.

Inadequate fuelling. Concurrent training is energy expensive. Both adaptations compete for substrate. Eating in a deficit during a concurrent build produces compromise in both directions. Aim for at least maintenance calories with adequate protein (1.6-2.2g/kg/day)  and a relatively high carbohydrate intake during a serious concurrent block.

Insufficient recovery. Concurrent training stacks central and peripheral fatigue from both modalities. Sleep needs to be protected aggressively. The Sunday rest day is non-negotiable. Skip recovery and you build neither quality.

What progress should actually look like in a concurrent block

Concurrent training doesn't stop progress in either quality. It slows the rate of progress in both, relative to what you'd see chasing one quality on its own. That's the trade, and it's worth stating plainly because it's where most tactical athletes lose confidence in an otherwise well-built programme.

The problem is one of reference points. A candidate reads a strength programme's expected numbers, then reads a running plan's expected numbers, and quietly assumes a concurrent block should deliver both. It won't. When the squat only moves 10kg in twelve weeks instead of the 25kg the internet and the Instagram guru promised, the conclusion is usually "oh the programme isn't working" rather than "the programme is doing two jobs at once, and I just need to chill the fuck out and just keep consistent and trust the process".

As a working estimate from coaching this for 20 years, expect somewhere around half to two-thirds of the rate of progress you'd see in a dedicated single-quality block. That figure is a coaching insight rather than a strict research finding, and it varies with the trainee, training age, actual age, sleep, food and how well the week is structured. But it's close enough to be useful, and it stops people writing off a block that's actually going fine, you're just impatient.

Training age matters here more than almost anything else. A soldier in their first two years of structured training will improve at nearly everything simultaneously, because their ceiling is a long way off in every direction. The interference effect is smaller in absolute terms and the newbie adaptation window covers a multitude of programming sins. The more trained you are, the more obvious the trade becomes, and the more you have to accept that something leads and the rest holds.

Table 5. Realistic expectations across a 12-week concurrent block, depending on which quality is leading. The block is working when the leading quality moves and the supporting quality holds.

Four things worth holding onto when you assess a block:

Don't expect simultaneous PBs. Squat, deadlift, 1.5-mile time, tab time and VO2 max are not all going up in the same twelve weeks. Something leads. The rest hold or creep up quietly. A block where every metric improved at once usually means either a very low training age or a test that wasn't hard enough.

Maintenance is a result. Holding a squat while your aerobic base climbs is the programme working exactly as designed. It only looks like stalling if you've forgotten which quality this block was biased towards. In an endurance-led phase, strength that hasn't moved has still been defended against a large volume of running, which is not nothing.

Judge it over blocks, not weeks. Test every 12-16 weeks. Week-to-week interpretation is close to useless when two qualities are being trained, because normal fatigue fluctuation is larger than the weekly signal you're trying to read. Session-to-session numbers will bounce around. That isn't usable data, it's just unhelpful noise.

Know what's leading. If you can't answer the question "which quality is this block biased towards?", you'll read every normal plateau as a failure and start changing things that didn't need changing. Decide the bias before the block starts, write it down, and assess against that.

The last point is the one that keeps people in a programme long enough for it to work. Most concurrent programmes don't fall over because the physiology was wrong. They fall over because someone got twelve weeks in, saw a flat bench press, and rewrote the whole thing during an endurance-led phase where a flat bench press was the intended outcome.

Bottom line

The interference effect is real, smaller than most fear, and almost entirely programmable around.

Tactical athletes can build meaningful strength and meaningful aerobic capacity in the same training block - provided the programming respects the molecular mechanism (separate hard sessions, control AMPK exposure), the variables that matter (volume, modality, order, intensity, recovery), and the strategic phasing (strength-priority blocks alternating with endurance-priority blocks).

Three principles to take into your training week:

• Separate hard cardio from hard strength. Hard intervals and heavy strength go on different days. Easy Zone 2 cardio sits between strength days. The interference window is largest in the 6-12 hours after a hard endurance session.

• Bias modality to the goal. Strength priority - favour cycling and rowing. Endurance priority - running takes precedence. Specificity still wins over interference avoidance when the test requires it.

• Eat, sleep, recover. Concurrent training is metabolically expensive. Protect sleep aggressively. Eat at maintenance or above. Treat the rest day as training. Skip these and the interference becomes a problem rather than a manageable variable.

Tactical athletes have never had the luxury of single-modality training. The job demands both qualities, simultaneously, indefinitely. Concurrent training is the only realistic answer - and programmed sensibly, it works.

Concurrent training: frequently asked questions

What is concurrent training?

Concurrent training is the simultaneous pursuit of both strength and endurance adaptations within the same training programme - typically across weeks and months, not a single session. For tactical athletes it's the default mode of training: every soldier preparing for selection is, by definition, training concurrently.

Will cardio kill my gains?

Not if it's programmed sensibly. The interference effect is real but typically modest, and almost entirely manageable through programming. The factors that matter are endurance volume (below 3 sessions per week is low-interference), modality (cycling and rowing produce less interference than running), order (strength before cardio in same-day sessions), recovery (24+ hours between hard sessions), and caloric intake (deficit magnifies interference). Get these right and the strength loss is typically 5% or less - a price most tactical athletes accept for the dual adaptation benefit.

Should I do cardio before or after weights?

Strength before cardio in the same session. Cardio before strength meaningfully degrades subsequent lifting performance - both through glycogen depletion and central nervous system fatigue. Where possible, separate by at least 6 hours. Morning strength, evening cardio is the gold standard when same-day is necessary.

How many times a week should I do cardio if I'm strength training?

For strength-priority phases, 2-3 cardio sessions per week is the sweet spot - enough to build and maintain aerobic capacity without significantly degrading strength gains. For endurance-priority phases, 4-5 cardio sessions per week with 2 maintenance-volume strength sessions works well. Above 5 cardio sessions per week, strength gains become harder to drive even with optimised programming.

Does running interfere with strength training more than cycling?

Yes, generally. Cycling is concentric-dominant and lacks the eccentric loading and impact damage of running. Studies consistently show less interference from cycling-based cardio than running at equivalent intensities and durations. For strength-priority phases, weight cycling higher in the cardio modality. Run when running specificity is required for your test.

Can I build muscle and lose fat at the same time?

Possible but slow, especially for trained athletes. A small caloric deficit (250-500 kcal below maintenance) with high protein intake (2.0-2.4g/kg) and resistance training can produce simultaneous body composition change - but the rate of either adaptation is slowed. For serious strength building, a maintenance or small surplus produces faster gains. For serious fat loss, more aggressive deficits work but interfere with both strength and endurance adaptation.

How long should rest days be in concurrent training?

One full rest day per week is the minimum for sustainable concurrent training. Two rest days per week (or one full rest + one mobility-only day) is the more sustainable distribution for serious training blocks. The CNS fatigue from stacking strength and high-intensity endurance accumulates faster than most lifters appreciate. Sleep is non-negotiable - 7-9 hours nightly during a concurrent block.

What does the interference effect actually feel like?

In practice: weight on the bar that felt easy two weeks ago suddenly feels heavy. Top-set reps drop. Recovery between sets feels longer. Bar speed is sluggish. The session is doable but the quality is degraded. This is usually a sign that the cardio volume has crept above the threshold your recovery capacity can support - or that hard cardio sessions have moved too close to hard strength sessions. Restructure the week, not the lifts.

Should beginners do concurrent training?

Yes, with one caveat. Beginners benefit from concurrent training because their adaptation ceiling is high in both directions and the interference effect is smaller (less trained athletes show smaller absolute interference). The caveat is total volume - beginners often try to do too much of both, producing fatigue without adaptation. Start with 2-3 strength sessions and 2-3 cardio sessions per week, distributed carefully, and progress from there.

How do I structure concurrent training during selection prep?

During the 12-16 weeks of focused selection prep, the distribution shifts to endurance-priority: 4-5 cardio sessions per week (mix of Zone 2, intervals, and loaded carries), 2 strength sessions per week (maintenance volume, compound lifts in the 3-6 rep range), and aggressive recovery management. Strength holds; cardio leads. Pre-selection is one of the most demanding concurrent training environments - every variable in the article above becomes more important, not less.

How fast should I expect to progress on a concurrent programme?

Slower in both qualities than you'd progress chasing either one alone, and that's the expected outcome rather than a fault in the programming. A reasonable working figure is half to two thirds of the rate you'd see in a dedicated single-quality block. Beginners progress faster in both directions because their adaptation ceiling is a long way off. Trained athletes see the trade more clearly. Assess over 12-16 week blocks, know which quality the block is biased towards, and treat maintenance of the supporting quality as a result rather than a stall.

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.

Wilson, J. M., Marin, P. J., Rhea, M. R., Wilson, S. M., 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.

Schumann, M., Feuerbacher, J. F., Sünkeler, M. et al. (2022). Compatibility of concurrent aerobic and strength training for skeletal muscle size and function: an updated systematic review and meta-analysis. Sports Medicine, 52(3), 601-612.

Murach, K. A., & Bagley, J. R. (2016). Skeletal muscle hypertrophy with concurrent exercise training: contrary evidence for an interference effect. Sports Medicine, 46(8), 1029-1039.

Coffey, V. G., & Hawley, J. A. (2017). Concurrent exercise training: do opposites distract? The Journal of Physiology, 595(11), 3461-3475.

Fyfe, J. J., Bishop, D. J., & Stepto, N. K. (2014). Interference between concurrent resistance and endurance exercise: molecular bases and the role of individual training variables. Sports Medicine, 44(6), 743-762.

The Stoic Conditioning programmes are built around concurrent training principles - every programme integrates strength, aerobic capacity, and load carriage with the timing, intensity, and recovery management this article describes.

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