The Interference Effect: How Real Is It for Non-Athletes?

By Olivia Bennett

Who This Matters Most For

What the Interference Effect Actually Is

The term describes a proposed conflict between resistance training and endurance training when both are performed by the same person over the same training block. The concern is biological: endurance work is thought to activate a cellular pathway built around an enzyme called AMPK, while resistance training activates a separate pathway built around mTOR, which drives muscle protein synthesis. In theory, heavy AMPK activation from repeated cardio sessions can blunt the mTOR signal that resistance training is trying to produce, leading to smaller strength and muscle gains than resistance training alone would deliver.

That mechanism is real at the cellular level, and it has been demonstrated in lab settings. What is less settled is how much it actually matters for the size of the muscle and strength gains a real person sees over weeks and months of training, outside a petri dish or a single-session biopsy study. That gap between “detectable at the molecular level” and “large enough to change your results” is the central question this article works through.

The idea entered the fitness world through a specific, frequently cited experiment, and understanding exactly what that experiment did (and did not) show is the first step toward figuring out whether it applies to you.

Why the Original Research Doesn’t Generalize Well

The interference effect traces back to a 1980 study by exercise physiologist Robert Hickson, published in the European Journal of Applied Physiology, that is still one of the most cited papers in strength and conditioning. Hickson split subjects into a strength-only group, an endurance-only group, and a combined group, then tracked leg strength and aerobic capacity over ten weeks. For the first several weeks, the combined group made strength gains alongside the strength-only group. Around week seven, their strength gains stalled and then started to decline, even as the strength-only group kept climbing.

The catch is in the training design, not just the result. Hickson’s combined group trained resistance and endurance on a near-daily basis, with total weekly training volume far higher than what a typical gym member does. This was not a study of someone lifting three times a week and jogging twice a week. It was closer to a mini training-camp protocol, the kind of volume load you would associate with an athlete building toward a specific competitive peak, not someone trying to stay fit and strong around a full-time job.

This distinction matters because dose is central to how interference behaves. A high enough combined training load can outstrip anyone’s recovery capacity, athlete or beginner, and produce a plateau or regression that has more to do with accumulated fatigue than with a specific molecular tug-of-war between two training pathways. When later researchers tried to replicate strong interference effects using training frequencies and volumes closer to what recreational exercisers actually do, three or four sessions of each type per week, with normal rest days built in, the effect shrank considerably or disappeared for the outcomes most people care about: maximal strength and muscle size.

In other words, the original alarm was raised using a protocol that front-loaded fatigue in a way most non-athletes never come close to replicating. That does not make the original finding wrong. It makes it a data point about what happens under an extreme, athlete-caliber training load, not a general rule for the person doing a lifting split and a couple of easy runs each week.

What Recent Research Actually Shows for Typical Gym-Goers

The clearest modern answer comes from a 2022 systematic review and meta-analysis by Schumann and colleagues, published in Sports Medicine, which pooled 43 studies and roughly 1,090 participants comparing concurrent training against resistance training alone. The results were reassuring for most goals: there was no statistically meaningful interference for maximal strength (standardized mean difference of -0.06) and no meaningful interference for muscle hypertrophy (standardized mean difference of -0.01). The one outcome that did show a real, if moderate, reduction was explosive or power-based strength (standardized mean difference of -0.28), and that reduction was concentrated specifically in protocols where aerobic and resistance work were performed back-to-back in the same session rather than separated by a few hours.

A 2024 meta-analysis by Huiberts, Wüst, and van der Zwaard, also in Sports Medicine, dug further into who is affected and how, pooling 59 studies and about 1,346 participants. It found a modest interference effect on lower-body strength specifically in men (standardized mean difference of roughly -0.43), while women in the pooled data did not show the same pattern. It also found that untrained endurance participants tended to gain less aerobic capacity from concurrent training than trained endurance participants did, though strength outcomes did not differ meaningfully by training status. This is a useful, if slightly counterintuitive, piece of the picture: training status changed the cardio side of the equation more clearly than it changed the strength side.

A 2026 umbrella review by Held and colleagues in Sports Medicine, which synthesized 17 separate meta-analyses covering 144 underlying studies and roughly 1,492 participants, reached a similarly practical conclusion: concurrent training produced meaningfully greater strength adaptations than endurance training alone, and it preserved most of the strength, power, and hypertrophy benefits of resistance-only training while still delivering the aerobic fitness gains of endurance-only training. The review’s authors specifically described concurrent training as a sound strategy for recreationally trained individuals, while noting that evidence in elite athlete populations remains comparatively thin, which is itself a telling detail: much of what people assume about interference in elite athletes is inferred and extrapolated rather than directly measured in that population.

Put together, the newer, larger, better-controlled body of research points in one direction: the interference effect is real as a phenomenon, but its practical size for a recreational trainee’s strength and muscle gains is small enough that, for most people, it should not be a primary factor in deciding whether to combine training types.

The Variables That Actually Matter

Instead of asking “does the interference effect exist,” a more useful question is “which specific factors turn a small, mostly irrelevant effect into a real one.” Across the meta-analytic evidence, three variables come up repeatedly.

Session proximity. This is the single most consistent finding across the literature. Doing hard cardio and heavy lifting in the same session, especially cardio right before lifting, appears to blunt performance and power adaptations more than spacing the two out. Schumann’s team found the power-strength interference was tied specifically to same-session training; separating sessions by roughly three hours or more, or simply training on different days, largely removed the effect for that outcome.

Training frequency and total volume. Interference becomes more plausible as combined weekly volume climbs into territory that outpaces recovery, which is exactly what happened in Hickson’s near-daily protocol. Across the pooled recreational-population data, moderate frequency, three to five resistance sessions and two to four cardio sessions per week, has not shown the same pattern. The determining factor looks less like “are you doing two types of training” and more like “is your total weekly workload realistic for your recovery capacity.”

Training status and experience. The 2024 Huiberts meta-analysis found that untrained endurance participants got less aerobic benefit from concurrent training than trained endurance participants, while strength outcomes were not clearly moderated by training status. Beginners in general tend to be more resilient to combined training stress simply because almost any structured training produces adaptation for them; the room for one training mode to meaningfully blunt the other is smaller when a person is far from their genetic ceiling in either quality.

Elite Athletes vs. Recreational Trainees: How Interference Compares

What Increases vs. Decreases Interference Risk

Checklist: Should You Actually Worry About Interference?

Worked Example: A Realistic Recreational Lifter

Consider a 34-year-old who lifts four days a week on an upper/lower split and wants to add two 30-minute jogs a week to improve cardiovascular health, without losing the strength and muscle progress built up over the past year. Based on the research described above, the practical plan is straightforward: keep the jogs on days separate from the heaviest lower-body lifting session, or if a same-day combination is unavoidable, lift first and jog several hours later rather than jogging right before squats. Total weekly training volume, four lifting sessions plus two short runs, sits well within the range studied in the recreational-population meta-analyses, so there is little reason to expect a measurable strength or hypertrophy cost.

The more useful thing for this person to track is not some theoretical interference penalty but the two variables that actually predict outcomes in the pooled data: total weekly load relative to recovery, and whether hard sessions of each type are stacked or spaced. As long as sleep, food intake, and total volume stay reasonable, the expected outcome, based on the current evidence, is continued strength and muscle progress alongside real gains in aerobic fitness.

Common Mistakes: Overestimating Interference Risk

What Exercise Scientists Say

Researchers who have re-examined this question in the last few years tend to land in a similar place: the interference effect is a genuine physiological phenomenon that is easy to demonstrate under controlled, high-dose conditions, but it is not a strong predictor of outcomes for the training volumes most non-athletes actually use. The authors of the 2022 Schumann meta-analysis concluded that concurrent training does not meaningfully compromise maximal strength or hypertrophy, with the caveat that explosive strength is more sensitive to same-session programming choices. The authors of the 2026 Held umbrella review went further, describing concurrent training as a sound strategy for recreationally trained individuals seeking both strength and cardiovascular benefits, while flagging that elite-athlete evidence is thinner and less conclusive than commonly assumed.

The practical guidance that follows from this body of work is consistent across sources: separate hard cardio and heavy lifting by a few hours when possible, keep total combined volume proportional to your recovery capacity, and reserve the more cautious, athlete-style programming rules for people whose performance in a specific power or speed outcome is being professionally evaluated.

Key Takeaways

Frequently Asked Questions

References