How to Combine Cardio and Strength Training: Research Review

If you’re anything like me you’ve probably wondered how best to combine cardio and strength training. I can tell you from experience that the vast majority of athletes do this incorrectly. This article is going to cover the scientific basis for pairing cardio and strength training to make sure that you don’t needlessly lose strength and muscle mass.

There are a couple of reasons why you might want to combine these two types of training. First, and most common, is to lose body fat. Research consistently points towards a drastic decrease in body fat when both are paired together. It is much more effective than just doing endurance training or strength training.

The second reason a person might combine these two are for performance reasons. Functional fitness athletes will often find that increasing their conditioning drastically improves their WOD and metcon performance. Unfortunately, they cannot rely on just cardio or strength to do well. They must have a balance of both, especially if they have competitive aspirations.

Before we go any further let’s cover some of the key points up front.

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• Performing cardio and strength training has little to no effect on upper body size or strength
• Longer durations of endurance training are associated with decreases in strength and power
• Running with strength training is the most effective pairing to reduce fat mass
• Cycling with strength training is the most effective pairing to maintain strength and muscle mass

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Cardio Effects on Strength, Power, and Muscle Mass

I’m going to be honest here, there is no free lunch. If you decide to train both cardio and strength, you will slow down the rate of strength gain. There is no way around this. The good news is that there are ways to pair them so this interference is minimized.

In a recent meta analysis (research review of all relevant studies) researchers determined that upper body strength and muscle size was least effected by combining lifting with cardio, but lower body measures of strength, size, and power were affected.

You can see from this figure that pure endurance training has little to no effect on any measure of muscle size, strength, or power. You can also see that pure strength training is always superior to combined cardio and resistance training (labelled as concurrent training) for gaining strength.

The vertical axis is labelled as the effect size, which is defined as a measure of statistical strength between two variables. For our purposes the bigger the effect size, the stronger the relationship.

I found it particularly interesting that V02 max (the amount of oxygen your body can use) was superior in concurrent training. I wasn’t surprised to note that combining cardio and strength training caused the most fat loss. I guess bodybuilders have been doing something right all these years!

There is one key thing I want to point out, that is rarely covered in most articles. This type of data shows less measurable improvement in strength, power, and muscle mass for a relatively short time frame. It does not show that you cannot reach the same levels of strength, or muscularity given a longer time frame. Consider this analogy.

If you were going to school to be a lawyer and a doctor, it would take you much longer to do both, compared to someone going to school to be one or the other. However, once you’d finished all your training you would be able to do things that someone in either group could not. Just because you cannot get the same results in a specific time period doesn’t mean that you can’t have them ever. It will simply take a little longer to get there, but the reward will certainly be worth the wait!

Cardio and Strength Training: Session Duration

This is one of the key factors that determines what impact your endurance training will have on strength and muscle mass. You’ll find that as the session duration increases, the amount of muscle mass and strength you can gain decreases.

This graph really demonstrates that once you start to perform more than 60 minutes of cardio per day you will start to see almost no appreciably gain in strength, power, or muscular size (hypertrophy).

For readers of this article, we will be most concerned with maintaining strength and size, which means that we need to limit our session durations to no more than 30 minutes per day. However, if you did need a lot of conditioning work you could go up 40 minutes, but it would be less than ideal for your strength and size gains.

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Cardio and Strength: Sessions Per Week

Naturally, you’ll be wondering how many sessions per week are ideal now that we know that each session should be 30 minutes or less. Wouldn’t you know it, the researchers have a great chart for that as well.

There is a clear dose response relationship demonstrated in this chart. The more days you spend doing cardio, the larger the impact it will have on strength, power, and hypertrophy.

I would caution readers to interpret this chart with a grain of salt. I don’t really think that 4 days per week is actually worse than 5 days per week for gaining muscle. I think there was probably one study that skewed the results here.

As a coach, I look at this chart and I see that one day provides the least interference, but that probably won’t provide a particularly strong conditioning effect. For me, the sweet spot is going to be 3 days per week. This would allow for three sessions per week at 30 minutes or less. When combined with a hard strength program, this will ensure a strong conditioning effect.

Cardio and Strength: Choosing Your Cardio Equipment

We’ve discussed the duration, and total number of sessions that you should perform to maximize strength, and hypertrophy. Now we need to discuss the type of cardio modality we should choose to decrease interference effects.

This figure shows that running paired with strength training causes the most reduction in lower body strength, hypertrophy, and power. Cycling has much less of an interference effect, but it still slows the rate of strength and muscular increase. This sounds pretty straight forward right? The gym bros were right, don’t run!

Not so fast there. While running does cause the most interference, it also causes the most fat loss by a wide margin. You can see that cycling actually did not cause any further fat loss than pure strength training. If losing body fat is your goal, then running would still be an excellent option.

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While we are discussing body fat loss. I should point out that the researchers found another interesting relationship between heart rate and the amount of body fat that was lost.

This figure clearly shows a drastic increase in the fat loss for endurance training above 80% of an athlete’s maximum heart rate. For the majority of athletes, this will be training around 145-155 beats per minute. This heart rate is right where your body starts to transition from aerobic endurance to anaerobic endurance.

Cardio and Strength: Easy Cardio or High Intensity?

This is a key question, especially for functional fitness athletes, and those with competitive hopes. To answer this we will discuss an excellent study, where researchers compared resistance training + HIIT (Tabata protocol) or resistance training + continuous moderate intensity training.

Research participants were high level rugby and ice hockey players who had a long history of strength training. All could back squat 1.7x their bodyweight at a minimum. All participants completed 6 weeks of concurrent training, 3 times weekly, with half performing heavy squats, then moderate intensity cardio for 40-80 min per week. The other half performed the same squats, and then did a tabata protocol (8 x 20sec on / 10 sec off) for several blocks. All endurance work was done on a stationary cycle.

The researchers found that the moderate intensity cardio group increased their back squat strength by 14% where as the HIIT group increased their back squat strength by 12%. I would caution you here. That two percent difference is probably not significant, as there were only 6 participants in each group. I would imagine with more participants you would see the same strength gain.

More importantly, they showed that the only group to increase their VO2 max was the HIIT group. Moreover, the HIIT group actually gained a small amount of lean muscle mass, while the moderate intensity cardio group did not.

Cardio and Strength: How Long Between Each Session

This is a critical question for athletes and coaches looking to put together the most effective program they can. Research seems to indicate that achieving as much separation as possible is key to reducing the effect that endurance training has on strength, power, and muscle size.

Researchers noted that given 24 hours of separation, there was no discernible interference effect. Given this information you could alternate days and still make decent progress. Although, I would note that only strength training 3 days per week isn’t ideal for getting jacked or tan.

Other research has showed that 6 hours might be a more reasonable time to separate a cardio session from a strength session. This is more in line with what we see from most coaches who schedule an AM and PM session. Lastly, for athletes that have to perform strength and cardio in the same session, it is best to do your strength work first, and finish with your cardio.

Cardio and Strength: Summary

There has been a lot of info in this article, and a lot of points to consider. Remember, this is a summary of the current body of research regarding combining cardio and strength training. However, as coaches and athletes, we need to consider the practical implications of their findings.

For athletes that primarily need more conditioning, I would likely prescribe three sessions per week of endurance focused training. All sessions would be less than 30 minutes in length. I would program 2 HIIT sessions and one moderate intensity session as well. I would also plan 4-6 strength sessions per week, with at least one full rest day. This hypothetical week would look like this.

You can see that this template has the athlete performing three conditioning sessions per week, 5 WODs per week, and extra strength accessory moves. They will also be hitting all major muscle groups twice per week which research and practical experience shows a good ratio for most functional fitness athletes.

Obviously, there is much more we could talk about, such as total lifting volume, and the amount of sets each athlete needs to perform on this type of program. If you want to learn more about those specifics, then I’d recommend checking out the ebook below!

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