A while back, I received a message on Facebook from listener Lindsey. She said:

In another episode you talked about how aerobic exercise and weight lifting affect each other, but I’m not sure I understood. As a runner, can I run to the gym to lift weights and run home again or should I keep the cardio and weights on separate days? Thanks for your help!

After thanking Lindsey for her great question, I promised that I would do a deeper dive in the near future. I also told her that, in a nutshell, if she wants to get the fullest benefits of each workout, she should separate them. But since she is primarily a runner (and probably not too concerned about packing on as much muscle as possible), doing a short run to warm-up for and cool-down from a strength session is a great way to maximize her time and put a few more miles on her legs but not to do that every day. To be a good runner, she must also have dedicated run days.

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Now, if I were Lindsey, I would have written back and asked me a follow-up question that would have gone something like this: “If I do want to get the fullest benefits of each workout, how much would I have to separate those workouts by?”

Well, good question, imaginary Lindsey. Let’s look at that!

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Should you do cardio and weights in the same day?

A 2016 study, aiming to determine whether the amount of recovery between a strength and an aerobic workout influenced the response to the training program, concluded that fitness coaches should avoid scheduling two contradictory qualities (like running and weightlifting, or swimming and powerlifting) with less than a six-hour recovery period between them if the goal is to obtain full adaptive responses to each workout.

Avoid scheduling two contradictory activities with less than a six-hour recovery period between them.

So, like I told Lindsey, if your goal is to get strong, there is some significant detriment that cardio can have on strength development. This is true whether you do the cardio workout in the same workout, or if you simply do cardio less than six hours before your weight training.

The researchers who performed this study also stated that daily training without a recovery period between sessions (or training twice a day) is not optimal for neuromuscular and aerobic improvements. So ideally, if you want to get stronger, you should separate your cardio and strength workouts by more than six hours.

Now, this seems straightforward for someone like Lindsey who is mostly interested in running and is doing strength training because she is a smart runner who understands the value of pre-hab. But what if the event you are training for requires that you perform strength and cardio simultaneously? Like an obstacle course race, the CrossFit Games, or even a killer hike with a big pack on your back? Or perhaps your goal is simply to lose body fat. Well, that changes everything.

Combining weights and cardio

A study that aimed to investigate the effects of intrasession sequencing (the order) of concurrent resistance and endurance training on the serum leptin (the hormone that inhibits hunger), testosterone, cortisol (the stress hormone), and body composition in obese men, came to some cool conclusions.

The “weights before cardio” group were slightly better off in every single test, including fat loss.

Thirty obese young males were divided randomly into three groups that either performed weights before cardio, cardio before weights, or didn’t exercise at all. They trained three times a week for eight weeks. Their cardio workouts were made up of running at 70–80% of maximal heart rate for ten minutes and their weight training consisted of three sets of eight repetitions at 80% of one repetition max. The lifts they performed were leg extension, lying leg curl, tricep pushdown, bench press, and lateral pull down. Whether they did the cardio or weights first, all the workouts were separated by five minutes of recovery.

The results showed that for testosterone, there were no significant differences. For cortisol, they found significant increases in both of the training groups. There were significant decreases in the leptin and testosterone to cortisol ratio (which indicates a positive fitness response) and both training groups also had a significant loss of body fat. The interesting thing (and the take-home message) was that the “weights before cardio” group were slightly better off in every single test, including fat loss.

Why should you combine strength training and cardio?

Cardio (or aerobic exercise) is known to benefit your health and boost your fitness levels because it increases the density of some important cardiovascular components, like tiny blood-carrying capillaries. It is also known to build your mitochondria (your cellular power plants), assist with achieving and maintaining healthy cholesterol levels, increase or maintain blood vessel flexibility, help with fat loss, and the list goes on and on.

It’s clear that doing a combination of both cardio and resistance training is the best way to increase health markers.

Strength training (also called resistance or weight training) has also been shown to have a significant impact on cholesterol levels, hormone levels, strength, lean body mass, bone density, ligament strength, tendon health, and fat loss.

So, if we put the two together, it’s clear that doing a combination of both cardio and resistance training is the best way to increase health markers, boost fitness levels, and also that golden goose, maximize fat loss. But it’s still not clear in what order.

You may be interested to know that research shows a greater total amount of calories are burned when cardio is done first, followed by weightlifting. So if simply burning calories is your main (and uninspired) goal, there’s that. But we fit folks are interested in much more than just calories, right?

Cardio before weights for fat loss?

A study in the Journal of Strength & Conditioning Research looked into whether the order of resistance training and endurance exercise during a workout affects fat loss. Over the course of eight weeks, they investigated the effects that ordering and reordering workouts had on strength, VO2max, body weight, body fat percentage, and lean body mass.

A collection of previously inactive college females were randomly assigned to do their resistance training workout either before some endurance training or after it. Their training program consisted of four workouts per week, with each workout lasting one hour.

The cardio component of the workout lasted 30 minutes and was done at a “moderate intensity.”

The heavy lifting part of the workout had the subjects doing a three-way split routine (chest and back, shoulders and arms, and lower body). During this workout, they would perform three sets of 8–12 repetitions for 5–6 different exercises.

Whether they did the cardio first or the weights first, the rest period was no more than 5 minutes.

After doing eight weeks of combined endurance and resistance training, they all experienced significant improvements in VO2max, strength, and lean body mass. But unlike the obese males in the earlier study, it was concluded that there was no difference in effect based on exercise order of weights before cardio or cardio before weights. In addition, and this is important to note, the only participants who saw significant changes in their body fat percentage were the ones who also made dietary changes.

Do you need to do cardio?

A recent study examined the effects of long-term endurance running and intense resistance training on central hemodynamics and answered the question: Can Weight Training Count as Cardio? They found that weight training is not only healthy for your heart but also, if the weight training is of adequate intensity and is performed in a controlled way that places stress on the muscles, it is absolutely going to give you a cardio workout as well.

If you are unsure about what I mean by “adequate intensity” well, to be “adequate” your heart rate should be above 60% of your max heart rate by the end of a single weight training set. For an easy way to estimate (and I do mean estimate) what your max heart rate is, just subtract your age from the number 220. My max heart rate is approximately 175 so those nosey folks out there can reverse engineer that to figure out approximately how old I am.

Weight training is not only healthy for your heart but also, if the weight training is of adequate intensity … it is absolutely going to give you a cardio workout as well.

If you are having trouble getting your heart rate even close to 60% or “adequate intensity,” try slowing down your lifting and resisting. Somewhere between 5-10 seconds up and 5-10 seconds down should do.

By spending more time on each lift, you will place more strain on the muscles, which demands more oxygen from the blood, which will demand more blood from the heart, which will make the heart beat harder and faster. Boom: adequate intensity and cardio!

What about mixing cardio and weights in the same workout?

The only thing we haven’t looked at yet is actually mixing the two together, not one followed by the other but repeatedly alternating them back and forth. This combo option involves brief bursts of cardio between each weight training set and this can make for a very effective, time-saving, and metabolism-boosting workout.

You must be able to maintain good form during your weight training exercises or you will find yourself standing in line at the physiotherapist or chiropractor’s office.

First off, a word of caution. If you are going to go for the mixed option, keep in mind that you must be able to maintain good form during your weight training exercises or you will find yourself standing in line at the physiotherapist or chiropractor’s office.

In 2008 the University of California evaluated the effects of concurrent strength and aerobic endurance training on muscle strength and endurance, body composition, and flexibility in female college athletes. To do this they had one group of athletes do only cardio, another group do only resistance training, and a final group do a concurrent training workout in which they would run like the wind for 30-60 seconds after completing each heavy lifting set.

Even though each group did what the researchers called “the same amount of work,” the group that mixed the cardio and weights experienced a 35% greater improvement in lower body strength, a 53% greater improvement in lower body endurance, a 28% greater improvement in lower body flexibility, a 144% greater improvement in upper body flexibility, an 82% greater improvement in muscle gains, and a hard to believe 991% greater loss in fat mass. What?!

That means the mixed group managed to burn fat and build muscle at the same time, and they also burned ten times the amount of body fat that was burned by the said groups that did cardio or resistance training only.

Should you combine weights and cardio?

When you are trying to get or stay fit, it can help to do a combination of endurance and resistance training—but that is not always optimal for your fitness goals. And choosing which you should do first is often a matter of determining what those goals are. For example Lindsey, who kicked off this entire topic, whose goal is to run better, we know that she can combine her strength work with some short cardio without jeopardizing her performance, as long as she is getting dedicated run training done on her non-lifting days.

Choosing which you should do first is often a matter of determining what your goals are.

If your focus is not to burn fat but to build strength, stick to doing your resistance training as a separate workout. If you’re training for endurance, focus on a high-quality cardio workout that isn’t interrupted by strength training. If your focus is pure fat loss, then you should strongly consider combining your weight lifting and cardio in one workout.

But without splitting too many hairs, if you simply don’t have time to do a separate strength and a separate cardio workout, then just do it all in one big workout—I mean, come on. How many of us are actually hoping to compete in the Olympics after all? As we saw in the study on the inactive college females, no matter what order they did the workouts in, they all saw improvements in VO2max, strength, and lean body mass and for the most part, isn’t that what we are all hoping for?