What Happens If You Only Lift Weights Without Doing Cardio?

There are a number of dedicated gym enthusiasts that lift weights but never set foot on a piece of cardio equipment. Cross training, which means training using multiple modalities, is considered the best path to improvement of overall health. An individual who implements cross training would lift weights, perform cardio, take yoga classes, play a sport, etc.

For one reason or another, some people may not be able to do this. It could be due to time constraints or a general distaste for a certain type of exercise.

You may wonder what the downsides are of lifting while totally negating cardiovascular exercise.

There is no inherent danger to doing zero cardio and totally focusing on weightlifting. Depending on the type of gym you go to, most of the people there probably follow that protocol. However, there are advantages to doing at least some cardio that many are unaware of.

Oftentimes there is a fear that cardio is a recipe to impede muscle growth. When a lifter thinks of a person who specializes in cardiovascular exercise, they picture a marathon runner with a skinny frame and low levels of muscle mass.

But it doesn’t quite work that way. That individual who runs dozens of miles per week has different goals, and thus follows a completely different training program and diet. A person dedicated to lifting weights at the gym won’t have to worry about muscle simply disappearing by adding a little cardio to the routine.

The conversation then shifts from saying that you not only can do cardio, but that there are reasons you should do cardio.

Here’s what happens if you skip cardio completely and only hit the weights.

1. You May Be Leaving Muscle Gains on the Table

An individual’s level of cardiovascular endurance has an effect of the maximum amount of muscle that can be built. Any strenuous set of a resistance training exercise, whether squats, bench press, rows, or something similar, will leave you gasping for air at the end.

Building muscle, especially as you reach intermediate to advanced levels of lifting weights, requires you to take sets relatively close to failure. At this stage of lifting, muscle will only grow when it is pushed to the limit.

Let’s say for example you are doing a set of bench press to failure. You have a spotter there for safety so you can truly perform to your maximum capabilities. Let’s also assume that cardio is not part of this workout program at all.

You reach 18 reps and have nothing left. You rack the barbell and get up huffing and puffing as your heartbeat pounds in your chest.

It’s fair to say that a similar individual who implements cardio into their routine would be able to grind out another 2-3 reps. Muscular endurance is a major factor in sets to failure and cardio would undoubtedly improve that. Cardio allowed this hypothetical person to add more volume to that crucial set, and workout volume is a major factor in muscle growth.

The automatic follow-up question would be: when the primary goal is to build muscle, what is the optimal amount of cardio to add to a program?

Obviously, too much cardio would be a detriment. A heavy abundance of low intensity, long duration cardio would promote type I (slow twitch) fiber accumulation. Weightlifting and muscle growth is more akin to type II (fast twitch) fibers.

There is also a phenomenon known as the interference effect, where cardio can block the potential for muscle gain if the two are performed too close to one another. This would occur if, for example, someone performed a resistance training workout and then ran on the treadmill for an hour.

The reason this occurs is due to the relationship between AMPK (released during cardio) and mTOR (released during weight training).

New research has indicated that perhaps the interference effect isn’t as strong as once thought. At this point it’s probably safe to say that too much cardio would still have a negative impact on building maximum amounts of muscle. But hopping on the stairmaster for a 10 minute warm-up certainly does not fall into that category.

The optimal amount of cardio to improve muscular endurance without being a detriment to muscle gain is 1-2 sessions of 30-45 minutes per week. Ideally this would be on a separate day from a lifting session.

This frequency would allow for an improvement in cardiovascular endurance without hampering muscle growth. On the contrary, cardio should indirectly improve muscle growth by allowing the individual to do more work in a resistance training session. This is due to cardiovascular endurance no longer being a limiting factor to maximum workout volume.

2. You’re Not Fully Optimizing Overall Health

While many people lift weights for aesthetic reasons, others do so to improve their health.

Muscle loss is a major problem for people as they age. Unfortunately some people experience a negative quality of life due to a lack of strength and muscle mass as they reach an advanced age. This is particularly evident in people who get injured and don’t have the physical means to recover properly.

As elementary as it sounds, an easy way to prevent against muscle loss is to build it at a young age and maintain as much as possible later on.

From an exercise perspective, there are many factors that go into optimizing one’s health. Having good cardiovascular endurance is correlated with many positive health outcomes. Someone who focuses solely on lifting weights without cardio would obviously not be optimizing their health to the highest degree.

Cardio encompasses many different types of exercise. A walk in the park and an intense game of 5 on 5 full court basketball are both technically considered cardio, but are quite different in nature.

Luckily there are protocols that you can follow to get the most out of your cardiovascular training. The ironic thing is that the low intensity and high intensity bouts both have their place since they both have unique benefits.

The easiest rule of thumb when it comes to optimizing cardio for health is variety; not in the type of cardio but in the intensity.

If you are performing 3 cardio sessions per week, each one should have a specific intensity. For example, one cardio session’s goal should be to reach your maximum heart rate. It should be so hard that you are bent over gasping for air with little ability to even form words in a conversation.

This activity will be so challenging that you will only be able to do it for 30-60 seconds before becoming completely fatigued. Exercise like this often leads to the “burning” feeling in muscles.

The second session should be moderate to high intensity but of a longer duration. An example would be running 2-3 miles for speed. This is beyond a light jog since the idea is to go as fast as possible, but obviously not to the extent of a full on sprint.

The final session is the longest and will be low to moderate intensity. This would be like an hour long bike ride or a hike up a mountain. It’s challenging, but still doable over a long period of time.

For individuals who want to begin cardio training but haven’t done so in a long time, exercise selection is critically important. Choose low impact cardio modalities like cycling or swimming, as these will result in minimal soreness and injury risk compared to high impact activities like running or CrossFit-type training.

If you choose to implement this new cardio routine in addition to weight training, whether for the sake of health or just to become a more well-rounded athlete, it’s important not to overcomplicate the process.

While helpful, it’s not necessary to use sophisticated heart rate monitors. Finding the right intensity for each cardio modality takes some trial and error, but over time you will gain a grasp of the level of exertion necessary to get the most out of each workout.