For years, lifters have been told that too much cardio will kill their gains. The concern is based on what is known as the interference effect, which suggests that combining cardiovascular and resistance training may reduce the strength or hypertrophy adaptations that would occur from resistance training alone.

I have always had questions about how broadly this idea gets applied. Muscle growth still requires a sufficient training stimulus, adequate protein, enough total energy and recovery. If those needs are being met, it never made sense to me that cardiovascular exercise would automatically eliminate the body’s ability to add muscle tissue. It seemed more likely that the way the training was programmed would matter far more than simply including cardio.

Newer research supports that idea. Conceição et al. (2026) compared resistance training alone with concurrent training that combined resistance exercise and long interval high intensity interval training. After 16 weeks, concurrent training did not inhibit muscle protein synthesis, satellite cell activity or type II muscle fiber hypertrophy. Both groups increased type II fiber size. The concurrent group also improved aerobic capacity, although strength gains were greater in the resistance training only group.

That distinction matters. The study did not show that every adaptation was identical. It showed that cardiovascular training did not prevent the molecular and muscular processes associated with hypertrophy. If maximal strength is the primary goal, fatigue and training specificity still need to be managed. That is different from saying cardio kills muscle growth.

The broader research tells a similar story. Schumann et al. (2022) analyzed 43 studies involving 1,090 participants and found that concurrent aerobic and strength training did not compromise muscle hypertrophy or maximal strength compared with strength training alone. They did find a small negative effect on explosive strength, particularly when both forms of training were performed in the same session. Once again, the problem was not simply the presence of cardio. The details of the program mattered.

In my opinion, what many people call interference may often be a recovery and programming problem. If someone performs a large amount of exhausting cardio, does not eat enough, does not recover and then expects to produce high quality strength work, their progress may suffer. But that does not mean the cardiovascular training directly shut down muscle growth. The issue may be less about cardiovascular training interfering with muscle growth and more about fatigue interfering with training quality and recovery.

You can create an environment that supports muscle growth while also improving cardiovascular health. Resistance training should still provide enough mechanical tension and progressive overload. Protein and total energy intake should support the workload. The amount, intensity and placement of cardio should match the person’s goals and ability to recover. When strength, power or hypertrophy is the priority, the most demanding resistance work should be protected rather than buried underneath unnecessary fatigue.

This is also why I do not believe in separating fitness into rigid silos. Cardiovascular health and muscular development are both essential. A complete program should build the qualities a person needs without allowing one component to destroy the quality of another. That requires coaching, judgment and intentional programming.

The interference effect is not completely imaginary. It is simply more nuanced than the fitness industry often makes it sound. Excessive volume, poor sequencing, inadequate nutrition and insufficient recovery can interfere with progress. Properly programmed cardiovascular exercise does not automatically prevent someone from becoming stronger or building muscle.

Cardio does not kill gains. Poor programming can.

References

Conceição, M., Vechin, F. C., Telles, G., Lixandrão, M., Ribeiro, N., Costa, L. A. R., Hevia-Larraín, V., Scarpelli, M. C., Damas, F., Libardi, C. A., Camera, D. M., Hawley, J. A., & Ugrinowitsch, C. (2026). Concurrent training with long-interval HIIT does not impair skeletal muscle protein synthesis or hypertrophy: Little evidence of an “interference effect.” Journal of Applied Physiology, 140(2), 415–427. https://doi.org/10.1152/japplphysiol.00642.2025

Schumann, M., Feuerbacher, J. F., Sünkeler, M., Freitag, N., Rønnestad, B. R., Doma, K., & Lundberg, T. R. (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. https://doi.org/10.1007/s40279-021-01587-7