Does Cardio Kill Strength?

Written by:

Damect Dominguez

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Athletes looking to develop muscle mass and increase their strength are typically wary of cardio training—fearing that prolonged bouts of running, rowing, or other work that emphasizes stamina and endurance will have a detrimental impact on their strength. But, how realistic is this fear?

Well, I would argue that it depends on the type of cardio work that is being performed, and how regularly it is being performed. First of all, consider that cardiovascular exercise, also called cardiorespiratory exercise, is any exercise that gets the heart rate up and in turn improves oxygen consumption in the body. Now, within that definition, we can find traditional aerobic work such as running, rowing, biking and swimming—all of which have been programmed at the CrossFit Games. To be a well rounded athlete, one must possess a high level of cardiovascular endurance and stamina, and one of the best ways of testing that is through low-intensity exercise performed over long distances or duration.

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Yet to base a training program solely on developing an athlete’s cardiovascular endurance would be a mistake—especially if one is looking to increase strength. The demands of certain sports dictate the type of training that the athlete follows. For example, marathon runners need to run long distances as quickly as possible, so their training centers on building the efficiency of their cardiovascular system to pump blood and carry nutrients (and waste products) to and from their muscles over long periods—as well as generating maximal oxygen intake and time-to-exhaustion in endurance work. Strength training, on the other hand, centers on improving the efficiency of your central nervous system to recruit motor units in your muscle fibers to produce stronger contractions. This naturally leads to increases in strength, muscle size and power. In addition, long-distance runners and other endurance athletes don’t want to carry a lot of mass during competition, as it’ll slow them down and tax their systems. Hence why a long-distance runner tend to have a smaller frame while sprinters carry much more muscle mass.

So a training program that comprises solely of aerobic work will affect an athlete’s ability to produce power and gain strength, since they won’t be performing any exercises that requires them to do so. If you don’t train to improve these skills, they will regress.

But what about a program that uses resistance work concurrently with aerobic work? Will an athlete experience the same kind of strength loss in this type of training?

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Consider a 2012 study from the Journal of Strength and Conditioning Research. The report, which analyzed the findings of 21 previous studies, concluded that gains in muscular hypertrophy and strength did not vary significantly between training programs that combined aerobic exercise with resistance work and resistance-only training. With that being said, the authors of the report did note that power development was far lower in concurrent training versus resistance-only training.

Now, returning to the ACE’s definition of cardiovascular exercise, we can see that there is more than one way to gain the same benefits from cardiovascular training while maintaining or even improving strength.

Lifting lighter weight quickly with allocated rest periods is known as high intensity interval training (HIIT), and we do a lot of it in CrossFit. There are more structured versions of HIIT in CrossFit programming, such as Every Minute on the Minute (EMOM’s) or Tabata training (8 rounds of 20 seconds of work, 10 seconds of rest), but every athlete will rest at some point during most metcons. This style of training is proven to provide the same benefits as traditional cardio work (in fact, multiple studies show that body fat loss, fat oxidation and VO2 max development (the amount of oxygen you can use for a given task)  is far greater in HIIT training), while simultaneously providing strength-building potential.

A 2009 study, again from the Journal of Strength and Conditioning Research, had competitive cyclists complete 4 weeks of HIIT training involving 30-second sprints on a stationary cycle separated by 30 seconds of rest. One group utilized a higher resistance setting than the other (making it harder to peddle), but both groups peddled as fast as they could for each 30-second sprint. The researchers found that the resistance-trained group increased their testosterone levels by almost 100 percent. The other group experienced a 60 percent increase. Given that testosterone is a vital hormone for building muscle strength and mass, one can see that HIIT is a useful way of combining strength training with cardio work.

So, while pure strength training will always be superior for building mass, strength and power, and pure cardiovascular work will always be the best option for those seeking to improve maximal oxygen intake and time-to-exhaustion in endurance work, training both simultaneously is a great way to prevent loss in either area.

Photo courtesy of Ryan Litwiller/CC BY NC 2.0


About Damect Dominguez

Co-founder of BoxLife Magazine. Author: Training Day: 400+ Workouts to Incorporate in Your Training.

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