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Does Cardio Interfere With Muscle Growth?

By Douglas AraújoUpdated 2 min read

Exercise professional · creator of the Letz method

Short answer

The interference effect is real, but it is small and depends on volume, modality, and the proximity between sessions — not on simply doing cardio and resistance training in the same week. For most people, training both does not meaningfully impair muscle hypertrophy.

The true magnitude of the effect

Interference between cardio and resistance training is real and has been quantified in reviews across the field. What often surprises people is its magnitude: it is small, and the variables that modulate it are aerobic volume, exercise modality, and the interval between sessions.

Very high cardio volumes and sessions performed back-to-back with resistance training are more likely to cause interference. Running two or three times a week, kept separate from resistance training, is not the problem common belief makes it out to be.

HIIT or continuous cardio

When it comes to improving aerobic capacity, both interval training and continuous exercise work, with differences that depend on the outcome and the population. There is no universal superiority of one format over the other.

In practice, the decision usually comes down to time availability and personal tolerance, rather than inherent effectiveness.

The expectation that needs recalibrating

There is one area where conventional wisdom misses the mark even more than on interference: the role of exercise in fat loss. Exercise alone moves the needle on the scale far less than people anticipate.

What it does, and does well, is protect lean mass throughout the process and help sustain lost weight afterward. Judging a workout program by what it subtracts from the scale is measuring with the wrong tool.

Frequently asked questions

Can I run and do resistance training in the same week?

Yes. The interference effect is small and depends on high cardio volume and sessions performed too close together — not on combining both modalities within the same week.

Is it better to do cardio before or after resistance training?

The proximity between sessions is one of the variables that modulate interference, so separating them is the most conservative choice. When that is not possible, the difference tends to be small.

Does cardio burn muscle?

Not in those terms. What the scientific literature describes is a small interference effect on hypertrophic adaptations, modulated by volume and proximity — not muscle catabolism simply from doing cardio.

Registry rules cited here

  • Combining Aerobic and Resistance TrainingPerforming aerobic and resistance training in the same program does not compromise hypertrophy or maximal strength; only explosive strength may be attenuated, particularly within the same session.
  • Interval vs. Continuous TrainingHIIT and moderate continuous training produce similar body composition improvements; interval training improves VO2max more and requires less time.
  • The Role of Exercise in Fat LossExercise alone produces modest weight loss; combined with diet, it preserves lean mass and improves weight maintenance. Resistance training prevents nearly all muscle loss caused by a calorie deficit.
  • Weekly Volume: Sets per Muscle GroupMore weekly sets per muscle produce greater hypertrophy, with diminishing returns; for strength, moderate volumes already capture most of the gains.

Sources cited

Informational content about training and nutrition. It is not a recommendation, prescription or adjustment of any medication, and it does not replace assessment by your doctor or dietitian.

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