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Cardio and Muscle Gain: Everything You Need to Know

Avatar Nutrition Staff

October 9, 2017


“Yeah, no… don’t put me down for cardio”— a memorable line taken from Fat Amy in the movie Pitch Perfect.

However, like most Americans, maybe Amy should have partaken in some form of cardiovascular exercise…besides traditional running. Many benefits can be derived from endurance training. Not only health benefits, such as improving heart rate and blood pressure, but also physique benefits such as maintaining or losing body fat. But, even with these known benefits, you may be thinking “cardio can kill your gains”, but what does the science say?


Different Forms of Cardio

Just scrolling through a Google search of cardiovascular exercises can be overwhelming. Walking, running, cycling, swimming, etc. all count as cardio, even though the form of the various activities is unique. For this article’s purpose, we’ll treat all forms of cardio the same, and solely distinguish between the intensity of a given cardiovascular activity.

low intensity cardio

Intensity relates to how hard (or easy) a given exercise is. Low intensity cardio is defined by 30-40% of an individual’s heart rate reserve (HHR); whereas, high intensity cardio (HIIT/interval training) is defined by a HRR above 60%, with moderate intensity falling between those two values. Think of low intensity cardio as the type that you can do and still have a conversation with a friend while doing it. On the other hand, high intensity cardio is so hard that you cannot talk and you can only do this for about one minute before you are completely exhausted!


The Pros and Cons

There is an overwhelming amount of scientific data attesting to the health benefits of cardiovascular exercise. Cardiovascular disease, diabetes, certain forms of cancer, osteoporosis—can all be prevented and treated with simple cardio [1,2]!

The cardio does not have to be high-intensity and extremely exhausting to achieve health benefits. Relative to preventing cardiovascular disease, moderate intensity cardio has been shown to be very effective [3]. In support of this fact, the American College of Sports Medicine recommends that you should get at least 150 minutes of moderate intensity exercise per week. This amount of cardio is the minimum recommended dosage for you to get and maintain health benefits.

In addition to the health benefits associated with cardiovascular exercise, cardio has also been shown in numerous studies to lower body fat percentage and fat mass. In a four-week study that looked at body composition changes among women in a fasted and a non-fasted state, it was reported that an hour of cardio three-days per week resulted in significant losses of body weight and fat mass [4].  Interestingly, the amount of fat loss the women experienced in this study was no different in those who did their cardio in the fasted state as compared to those who completed their cardio in the fed state.

Disease prevention and looking better on the beach—these are two of the primary benefits of cardio.

But are there any drawbacks to doing cardo? Unfortunately, yes.

Research consistently shows that when lower-intensity cardio is combined with resistance training, both muscle hypertrophy and power production are suppressed [5,6]. Therefore, if your goal is to build as much muscle mass as possible, it is probably better to limit lower intensity cardio. The same is true for strength and power athletes (football players, powerlifters, etc.)—avoid low intensity cardio exercise because you may be sacrificing the training adaptations you need to excel in your sport.


Effects on Muscle Recovery

If you’ve been working out for any length of time, chances are you lifted too much weight, did too many reps, or took too many days off between workouts on an occasion or two. And when you did this, your body was very sore the next day, or for the next several days! While you likely refer to this feeling as pain or discomfort, the scientific term for this is ‘Delayed Onset Muscle Soreness’ or DOMS.

We know what causes DOMS—muscle damage due to unaccustomed exercise, particularly large quantities of eccentric muscle actions. What we don’t know for sure is the best way to treat DOMS and get rid of the pain and discomfort in as short of a time period as possible.

Some of the more common treatments include ice, massage, rest, and dietary supplements. Is it possible that aerobic exercise/cardio can help alleviate DOMS? Researchers from California State University sought to quantify the benefits—if any—of cardio for muscle recovery [7]. The researchers had a group of women perform resistance exercise that would induce DOMS in their leg muscles, and then they had them engage in one of three different muscle recovery strategies right after the soreness inducing exercise:

  • moderate-intensity cycling for 20 minutes
  • low-intensity cycling for 20 minutes
  • seated rest (no cardio) for 20 minutes

biking for cardioThe researchers then measured subjective pain levels (on a scale of 1-10) for the next four days. Interestingly, there was no improvement in the pain during the 4-day recovery period from any of the strategies utilized, meaning that low or moderate intensity cardio exercise was no better than just sitting! Other research supports this finding as well [8].

While cardio exercise may not be effective for alleviating DOMS in the longer term, it does provide temporary pain relief from DOMS [9]. So, if you’re really sore from your workout yesterday or even from a few days before and you are wanting temporary relief from this pain, then doing a session of cardio will be beneficial in the short term. You just need to be aware that the pain relief is temporary and will resume again after your cardio session [9].


Best Cardio for Muscle Gain

Cardio is good for your health, it helps you lose body fat, and it will temporarily alleviate muscle soreness. This is the good news. In contrast, low intensity cardio is not ideal for gaining muscle mass. But what about higher intensity cardio?  Does that have a positive impact on muscle growth?

Research shows that high-intensity cardio stimulates the release of anabolic hormones (testosterone, growth hormone, IGF-1) that are conducive to an environment of stimulating muscle growth [10]. A recent study clearly shows the potential that a high-intensity cardio program can have on increasing muscle mass. In this study, male and female subjects engaged in high intensity cardio exercise three times per week for 10 weeks [11].

The high-intensity cardio program consisted of four sets of 4 minutes running at ~90% heart rate max followed by three minutes of active rest.  At the end of the 10-week high-intensity cardio exercise program, the vastus lateralis (the outer thigh muscle) increased its cross-sectional area by over 10%! This was in comparison to no change in the cross-sectional area for the control group (whom did not engage in the high-intensity cardio program).


While this finding is pretty cool, we need to interpret it with some perspective. Yes, muscle mass was gained from high intensity cardio—but the gain was localized to the outer thigh muscle only—so thinking that high intensity cardio is going to add pounds of muscle to your entire physique is not true. In fact, there are multiple studies showing that high intensity cardio does not pack on muscle mass (12,13). The best way to interpret this and other studies is that of the two extremes of cardio (high intensity cardio and low intensity cardio)—high intensity cardio is more favorable if you are interested in carrying more muscle mass on your body. But please don’t think that the way to building muscle is to do high intensity cardio! If you want to build muscle mass, lift weights!



In recent years, exercise in the form of cardio has been maligned by many in the fitness industry. Much of the criticisms of cardio-based exercise are unfounded, as this article has pointed out. The benefits of cardio surpass the well-known health benefits, and include not only fat loss, but also short-term relief from muscle soreness. Also, the right kind of cardio—high intensity cardio—can be more friendly to you if your goal is to have more muscle mass.



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