Why you shouldn’t do cardio and weights in the same​ workout

Cardio or strength training?

Do we really have to choose between them?

We have been told that cardiovascular exercise is good for us, and strength training is good for us. However, research has indicated that these two types of workouts may not be so good for us together.

Let’s face it. We want to have it all.

Most of us want to have a flat stomach and rippling muscles, but we also want a healthy heart as well.

So we hit the gym and do our weight lifting circuit and then finish off our workout by jumping on the treadmill or elliptical to get in our cardio.

It sounds like the best of both worlds, so what’s the problem?

Recent research suggests that when we try to combine cardio with weight lifting in the same workout, we end up not doing either one of them as well.

The interference effect

Scientists have identified something they have labeled the “interference effect” which says that when we lift weights and run on the treadmill in the same workout, we are not getting the results from either of these workouts as we would if we did them at separate times.

Why is this?

It’s not exactly clear, but scientists have come up with a few theories.

First of all, the hormonal and neuromuscular effects of cardio exercises are generally very different than muscle building, which is why when you decide to do them both right after one another, they can interfere with one another and essentially confuse the body as to what it is trying to accomplish.

What this means is that the anabolic (muscle building) effects of your strength training are blunted by the mostly catabolic (muscle breakdown) effects of cardio endurance training.

At the same time, if you lift before your cardio session, you will probably have far less energy to run/row/jump than you would otherwise.

You are basically mixing two activities that have different goals, so it tends to cancel out some of the positive effects of both.

In other words, what’s good for the heart and lungs is not necessarily what’s best for building your muscles.

While the scientific community may not all agree as to why the interference effect occurs (fatigue, hormonal effects, or neuromuscular signaling) it seems pretty clear at this point that it does exists.

The one bit of good news is that according to at least one study, this interference effect is primarily limited to the rate of muscle growth (hypertrophy) and does not seem to have as big of an effect on the overall level of strength gains.

So what’s the solution? How can we eliminate or at least minimize this so-called interference effect?

Do cardio and strength training on separate days.

The first and probably most obvious way to eliminate the interference effect is to do your muscle building and cardio workouts on different days of the week.

Of course, this means that you’ll need to go to the gym twice as often (every day vs. every other day). You could also choose to do your cardio workout at home or outside of the gym.

If you have the time and your schedule allows you to go to the gym every day, this might be the ideal solution for many people because doing so helps to reinforce the daily exercise habit versus having a workout day followed by a “rest” day.

Separate cardio and strength workouts in the day

On the other hand, if you don’t have the time or energy to go to the gym every day, some studies have suggested that the interference effect can be minimized if you separate your cardio and weight lifting workouts by at least 6 hours.

This is my personal preference. I like to do my cardio workout first thing in the morning to help wake myself up and get ready for the day. Depending on my schedule, I may do anywhere from 20-45 minutes of cardio first thing in the morning and then strength train in the late afternoon or evening.

I don’t drive to the gym to get in my cardio workout. Depending on the weather and that particular day’s energy level, I may hop on the treadmill, bike, jump rope, or do some heavy bag boxing.

If I had a brutal workout the day before, I might just do a light jog, or if I’m feeling up to a challenge, I may drive to the local park and run some hill sprints.

I tend to get bored easily with doing the same workout day after day, so I try to emphasize flexibility and variety when it comes to cardio.

Not exactly two workouts a day.

Sometimes when I tell people about this, they get the impression that I’m essentially doing two-a-days and any normal person doesn’t have the time and energy for that type of thing, especially as we get older.

However, because I do my workout first thing in the morning and it’s only 20-45 minutes long, I don’t really see it as a workout, but more of a general warm-up for the rest of the day.

I purposely keep the duration of these activities short and the intensity moderate on the days that I will be strength training later.

The main idea here is to do something to get the heart rate up, keep the workout short, and adjust things to that particular day’s energy level so that I still have something left for my strength training later that day.

Now because I don’t usually lift weights every day, my cardio workouts can also be used as an active recovery type of thing with a light jog if I’m really feeling sore and beat up that day. Or sometimes I’ll kick it up a notch and make my cardio workout more intense if I know that I’m going to be sitting in front of my computer for the rest of the day.

I’ll be honest and tell you that on the weekends I’ll typically sleep in and then maybe do something active later in the day. Most of the time, however, I find myself out with the family not doing anything more strenuous than strolling through Target and searching for the nearest Starbucks.

The bottom line…

Because strength training and cardio endurance training use different energy systems and have different hormonal and neuromuscular responses, it’s often better not to do both activities during the same workout.

Research has suggested it’s better to either do cardio and muscle building workouts on alternating days or at least separate them by at least six hours or more.

Having said that, don’t let this “interference effect” be your excuse not to hop on the treadmill or hit the weights.

Keep in mind that “optimal” and “ideal” are relative terms and the best workout will always be the one you actually show up and do.

If your schedule allows you to separate these workouts either on alternate days or at least six hours that’s awesome, if not, just do what you can do and don’t worry about it. If all you can do is a combination strength and cardio workout, then do that and don’t use the interference effect as an excuse.


Tomiya S, Kikuchi N, Nakazato K. Moderate Intensity Cycling Exercise after Upper Extremity Resistance Training Interferes Response to Muscle Hypertrophy but Not Strength Gains. Journal of Sports Science & Medicine. 2017;16(3):391-395.

Kikuchi N, Yoshida S, Okuyama M, Nakazato K. The Effect of High-Intensity Interval Cycling Sprints Subsequent to Arm-Curl Exercise on Upper-Body Muscle Strength and Hypertrophy . J Strength Cond Res. 2016 Aug;30

Eddens L, van Someren K, Howatson G. The Role of Intra-Session Exercise Sequence in the Interference Effect: A Systematic Review with Meta-Analysis. Sports Med. 2017 Sep 15.

Wilson JM, Marin PJ, Rhea MR, Wilson SM, Loenneke JP, Anderson JC. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. J Strength Cond Res. 2012 Aug;26:2293-307.

Drew Kimble CSCS*D, CPT
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