Concurrent Training Interference: Does Cardio Hurt Gains?

Does cardio hurt gains? For muscle size and maximal strength, the current pooled evidence says no: Schumann 2022 found no interference with hypertrophy (SMD -0.01) or maximal strength (SMD -0.06) across 43 studies, while explosive strength gains were blunted (SMD -0.28), most when both were trained in one session.^[2] The newest large analysis, Huiberts 2024, found one more real cost: a small lower-body strength penalty in men that did not appear in women.^[12]

Concurrent training is the simultaneous pursuit of resistance and endurance adaptations within the same training week. Hickson opened the field in 1980: over a ten-week program, the group doing strength work alongside endurance work improved leg strength at the same rate as the strength-only group for seven weeks, then levelled off and actually declined in weeks nine and ten, while VO2 max rose normally.^[7] The phenomenon was named "interference" and the question of how, when, and how badly two opposing stimuli interfere has driven hundreds of trials since.

The current picture is meaningfully different from the Wilson 2012 meta-analysis that anchored a generation of strength coaches. In the newer pooled data the hypertrophy and maximal-strength penalties have largely disappeared, leaving explosive strength, and lower-body strength in men, as the outcomes that still show a measurable cost. This article walks through Wilson 2012, the Schumann 2022 update, the Huiberts 2024 sex and training-status analysis, a 2026 analysis of sprint intervals, what Markov 2023 does and does not tell us, and the practical splits that fall out.

The Wilson 2012 baseline

Wilson and colleagues pooled 21 concurrent-training trials in 2012, yielding 422 effect sizes across hypertrophy, strength, and power.^[1] The analysis reports mean effect sizes per training group rather than a single pooled interference term. Headline numbers:

• Hypertrophy: mean effect size 1.23 for strength training alone, 0.85 for concurrent training, 0.27 for endurance alone. Concurrent groups still grew, just less than strength-only groups.
• Strength: 1.76 strength-only, 1.44 concurrent, 0.78 endurance-only.
• Power: 0.91 strength-only, 0.55 concurrent, 0.11 endurance-only — the only outcome where all three groups differed significantly from one another, and the largest relative gap.
• Mode interaction: adding running, but not cycling, produced significant decrements in both hypertrophy and strength.
• Dose interaction: endurance frequency (r = -0.26 to -0.35) and endurance session duration (r = -0.29 to -0.75) both correlated negatively with hypertrophy, strength, and power.

The Wilson model became the canonical reference. It was easy to summarise in a single sentence: running hurts hypertrophy more than cycling, more endurance is worse, power is the most fragile outcome.

The Schumann 2022 update

Schumann and colleagues re-ran the question in 2022 across 43 studies, each comparing supervised concurrent training against an identical strength-training prescription with no aerobic work.^[2] Several findings reversed or shrank.

• Muscle hypertrophy: pooled SMD -0.01 (95% CI -0.16 to 0.18, p = 0.919). No detectable interference at all.
• Maximal strength: pooled SMD -0.06 (95% CI -0.20 to 0.09, p = 0.446). Not statistically significant.
• Explosive strength: pooled SMD -0.28 (95% CI -0.48 to -0.08, p = 0.007). The one outcome with a real penalty, and it survives the newer data.
• Session separation: the attenuation of explosive strength was more pronounced when both qualities were trained within the same session (p = 0.043) than when the sessions were separated by at least 3 hours.
• Moderators that did not matter: type of aerobic training (cycling vs running), concurrent frequency (more vs fewer than 5 weekly sessions), training status, and mean age (under vs over 40).

Neither paper tests why the results differ. Schumann's inclusion rule is one candidate: every trial had to compare concurrent training against an identical strength prescription, so the strength stimulus was matched, which Wilson's broader pool did not require. Until a meta-analysis tests program design as a moderator, read the older interference estimates as an upper bound rather than as the typical cost.

Does concurrent training affect men and women differently?

Huiberts, Wüst and van der Zwaard 2024 pooled 59 studies with 1,346 healthy adults aged 18 to 50, each training for at least four weeks, to ask whether sex and training status change the interference effect.^[12]

• Lower-body strength: blunted in men (SMD -0.43, 95% CI -0.64 to -0.22) but not in women (SMD 0.08, 95% CI -0.34 to 0.49); the difference between sexes was significant (p = 0.03).
• Upper-body strength, power and VO2max: no sex differences.
• Hypertrophy: the authors judged the muscle-size data insufficient to draw conclusions.
• Training status: untrained people, but not trained or highly trained endurance athletes, gained less VO2max when strength work was added. Strength and endurance training status changed nothing else.

Read with Schumann 2022, the practical message for a male lifter is that leg strength is the quality most worth protecting: keep hard running away from heavy lower-body days. The female data are thinner, and the authors call for more studies in women and in highly trained athletes.

Do sprint intervals interfere with strength?

A 2026 meta-analysis pooled nine randomised trials (177 adults) that added sprint interval training to resistance training.^[13] Against resistance training alone it found no difference in lower-body strength (SMD 0.01), upper-body strength (SMD -0.06), jump performance or sprint performance, and a clear VO2max gain (SMD 0.78). Short sprints of 10 seconds or less also improved jumping (SMD 0.41). The trials are small and short, so treat this as support for brief, hard intervals as a low-cost conditioning choice for lifters, not as proof that any amount of endurance work is free.

Markov 2023: does concurrent training still work in older adults?

Markov, Hauser, and Chaabene 2023 asked a different question from Wilson and Schumann.^[3] Rather than comparing concurrent training against strength training alone, they pooled 15 randomised controlled trials (566 participants, healthy adults aged 50 to 73) comparing concurrent training against a passive control. The question is not how much interference concurrent training costs, but whether the combined model delivers in a population where both strength and aerobic capacity are declining.

• Muscle strength: moderate positive effect (SMD 0.74).
• Muscle power: moderate positive effect (SMD 0.50).
• Cardiorespiratory endurance: small-to-moderate positive effect (SMD 0.48).
• Balance: no significant effect.
• Age and sex: adults over 65 (SMD 1.04) and females (SMD 1.05) showed larger strength improvements than adults 65 and under (0.60) and males (0.38), though none of the subgroup differences reached significance.

The authors also ran an independent single-training-factor analysis to guide prescription. It is a set of subgroup comparisons, not a moderator regression, and the differences between subgroups were not statistically significant — so read the following as a hierarchy of plausible prescriptions, not as measured dose-response curves:

• Frequency: three sessions per week produced larger strength effects (SMD 0.91) than four (0.55), while cardiorespiratory endurance only showed a moderate effect at four sessions per week (0.58).
• Session duration: 30 to 60 minutes favoured strength (0.99) and power (0.88) over 60 to 90 minutes (0.40 and 0.29), while endurance favoured the longer sessions (0.61 vs 0.34).
• Program length: 12 weeks produced the largest strength (0.87) and power (0.88) effects; endurance kept improving out to 21 weeks (0.62 vs 0.40).
• Endurance intensity: moderate-to-near-maximal endurance work produced effects on strength (0.64) and endurance (0.49); low-intensity endurance work produced none.
• Order and separation: strength before endurance within the same session gave the largest strength gains (1.00 vs 0.55 for separate sessions), whereas keeping the two in separate sessions favoured endurance (0.58 vs 0.49 for endurance before strength in one session).

Two cautions before carrying any of this into a lifter's program. The population is healthy 50-to-73-year-olds and the comparator is doing nothing — so these numbers say concurrent training works, not that one configuration interferes less than another. For the interference question in trained lifters, Wilson and Schumann remain the relevant pooled evidence.

The mechanism: AMPK-mTOR cross-talk

Atherton 2005 proposed the molecular mechanism that anchors the modern interference framework.^[6] Endurance work activates AMP-activated protein kinase (AMPK), a metabolic sensor that responds to depleted ATP and rising AMP. Resistance work activates the mTOR pathway, the master regulator of muscle protein synthesis. AMPK and mTOR have inhibitory cross-talk: when AMPK is high, mTOR signalling is suppressed.

The proposed consequence is that endurance work performed shortly before a resistance session blunts the anabolic signalling that follows it. How long that window lasts depends on the intensity and duration of the endurance work, and the time courses come from acute signalling studies rather than training trials. The practical "6-hour rule" therefore rests on training data, not on the molecular model alone.

Robineau and colleagues 2016 tested this directly.^[10] Fifty-eight amateur rugby players trained for seven weeks with 0, 6, or 24 hours of recovery between the strength and aerobic sequences, against strength-only and non-training controls. Maximal strength gains in the bench press and half squat were lower in the 0-hour group than in the 6-hour, 24-hour, and strength-only groups, and VO2peak gains were largest with 24 hours of separation. The authors' own recommendation is not to schedule the two qualities less than 6 hours apart.

Order of operations

If both modalities have to happen on the same day, which order is better? Eddens 2018 meta-analysed ten trials of intra-session sequence and found resistance-before-endurance favoured lower-body dynamic strength (weighted mean difference 6.9% change, 95% CI 2.0 to 11.9), with no effect of order on lower-body hypertrophy, static strength, maximal aerobic capacity, or body-fat percentage.^[8] Enright 2015, working with youth elite soccer players over five weeks, found no significant interaction for training order, though the effect-size comparison leaned toward putting strength work before soccer-specific endurance work.^[9]

Practical synthesis: when same-day work is unavoidable, do the priority modality first while the system is fresh. For a hypertrophy-priority block, lift first. For a VO2-max-priority block, run intervals first.

Endurance-mode and intensity interactions

Gergley 2009 compared cycle ergometry against incline treadmill walking as the endurance mode added to a 9-week lower-body strength program in 30 untrained participants.^[11] Both modes blunted leg-press 1RM gains relative to resistance-only training, but the cycling group kept significantly more of the strength gain than the treadmill group. The treadmill arm walked uphill rather than ran, and the trial is small, so it supports cycling for a lifter's endurance work without measuring what running itself costs.

Blagrove 2018 reviewed the strength-training literature for distance runners and found the other direction mostly positive: running economy and performance improve with added strength work, especially heavy and explosive lifting.^[5] Read with the pooled interference data, the cost runs mainly one way: lifting helps runners, while hard endurance work is what can cost a lifter explosive strength and, in men, lower-body strength.^[2][12]

Practical splits by goal

Synthesising the 2022 to 2026 evidence into programmable splits:

Hypertrophy priority (lifter who runs)
  Resistance:           4 sessions/week, full programmed volume
  Endurance:            2 sessions/week max
  Mode:                 cycling preferred over running
  Intensity:            zone 2 base + 1 short interval session
  Separation:           24 hours from any lifting session
  Expected interference: negligible for hypertrophy and maximal strength
                        (Schumann pooled SMD -0.01 and -0.06, neither
                        statistically significant)

Endurance priority (runner who lifts)
  Resistance:           2 sessions/week, heavy + explosive
  Endurance:            5–6 sessions/week, full volume
  Mode:                 running (the priority specificity)
  Lifting focus:        compound, low-rep, high-intent
  Separation:           lift on quality run days, after the run
                        AM run + PM lift, or vice versa
  Expected interference: small for running performance; explosive
                         strength is the outcome most likely to lag

Hybrid athlete (true concurrent)
  Resistance:           3–4 sessions/week
  Endurance:            3–4 sessions/week
  Mode:                 mix cycling + running, with running for race specificity
  Separation:           same-day if needed, prefer 6+ hours
  Order:                priority adaptation first
  Expected outcome:     cost concentrated in explosive strength rather
                         than size or maximal strength; total work
                         capacity exceeds either single-focus program

Where the meta-analyses still disagree

• Whether endurance modality matters. Wilson 2012 found that adding running, but not cycling, produced significant decrements in hypertrophy and strength; Schumann 2022 found no significant moderation by aerobic modality at all. The same split shows up on training frequency, which Wilson found correlated with worse outcomes and Schumann found non-significant.
• Acute versus chronic interference. Doma 2017 reviewed the effect running the other way: a single resistance session leaves residual fatigue that can degrade the quality of subsequent endurance sessions for hours to days when recovery is short.^[4] The review is explicit that the link between that acute cost and chronic endurance adaptation is not fully established.
• Concurrent training in older adults. Schumann 2022 includes both age groups and reports no significant moderation by age, but the older-adult sample is small.
• Female-specific data. Huiberts 2024 is the first pooled analysis to break interference out by sex, and it found the lower-body strength penalty in men only.^[12] The female sample is still small, so "no interference in women" is a finding to confirm, not a settled rule.
• Long-duration trials. Most studies run 8 to 12 weeks. The interference effect compounded over a year of concurrent training is largely extrapolated, not measured.

Cross-link tools

• 1RM Calculator tracks the strength outcome that interference is most likely to compromise on power-priority blocks.
• VO2 Max Estimator tracks the endurance outcome on the other side.
• Workout Volume Calculator manages the resistance volume that determines whether the interference window matters.

• Wilson 2012 set the field: concurrent groups gained less than strength-only groups on size, strength, and especially power, with the penalty tracking endurance modality, frequency, and duration.
• Schumann 2022 found no detectable interference for hypertrophy or maximal strength, leaving explosive strength as the one outcome with a significant penalty — largest when both qualities share a session.
• Huiberts 2024 found a small lower-body strength penalty in men (SMD -0.43) and none in women, with too few hypertrophy data to judge muscle size.
• Markov 2023 answers a different question and should not be read as an interference finding: in adults aged 50 to 73, concurrent training beat a passive control on strength, power, and cardiorespiratory endurance.
• The molecular mechanism is AMPK-mTOR cross-talk; separating sessions by 6 to 24 hours largely resolves the conflict.
• Practical splits cap endurance at 2 to 3 sessions for hypertrophy priority, prefer cycling, and put separation between modalities when possible.