Does Endurance exercise Interfere with Strength Training?

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I once heard a conversation between body builders that during certain periods of their training, they stay away from cardio like they would the plague.

Is this notion correct? What is the physiological basis behind this? If I want to get stronger and bigger, should I also stay away from cardio too? To answer this question, we will refer to an excellent review paper by Fyfe et al published in the journal Sports Medicine, entitled: "Interference between concurrent resistance and endurance exercise: Molecular bases and the role of individual training variables."


Main points:

  • Current evidence does suggest that doing endurance training along with resistance training is not as effective in increasing muscle mass, strength, and power vs just resistance training alone.
  • Conversely, resistance training seems to not really impact gains in aerobic fitness
  • Physiological basis: endurance-type training mainly activates different molecular pathways (ex. AMPK) vs resistance training (ex. mTOR). The pathways activated by endurance exercise may decrease protein synthesis and even increase protein breakdown, thus interfering with the processes necessary to build muscle. These conclusions are based on animal research models.
  • How much rest time is necessary between endurance training and resistance training is unknown
  • Which endurance training has the greatest interference effect on muscular fitness is unknown
  • How many endurance training sessions / week will lead to an interference effect? This is also unknown.


My observations:

It is clear from this review paper that the science is not conclusive as to the exact biological mechanisms that explain why endurance training seems to interfere with gains in strength, mass and power. The authors themselves point out that animal and cellular models may not accurately reflect what happens in a human body. Also, the science does not allow us to conclusively answer what exact amount, type, duration and frequency of endurance training will interfere with gains from resistance training. Finally, it needs to be emphasized that neither this paper nor any other scientific paper suggests endurance training will cause people to "never" gain muscle. To conclude that "if you do endurance training, you won't gain muscle" would be wholly inaccurate. The paper authors themselves note how most athletes train both modes because their sport requires it, and we can see that athletes like Lebron James, Cristiano Ronaldo, and their peers are exhibit A as to how people can indeed have muscular bodies and fitness while still being engaged in aerobic-type activities.


Bottom line: If your goal is overall fitness or to improve in athletics, doing both resistance training and aerobic training are necessary for performance, and will greatly benefit your health. You can still get "cut" "lean" and "muscular" even while incorporating endurance training into your routine. However, if your goal is just to put on loads of mass, only get stronger and more develop power, then perhaps sticking with resistance training and greatly limiting endurance training may be an approach to consider.

To read the review paper for yourself, please refer to the below reference.



J Fyfe, et al. Interference between Concurrent Resistance and Endurance Exercise: Molecular Bases and the Role of Individual Training Variables. Sports Med (2014) 44; 743 - 762

George Cho