Concurrent Training: The Interference Between Lifting and Cardio

Training

Sep 18

Concurrent Training (CT) involves using a combination of resistance training and endurance training to maximize your performance and results. Depending on the sport you’re trying to excel in, concurrent training may be necessary to enhance your skillset and technique. But for pure power sports or pure endurance sports, concurrent training could potentially elicit an unwanted adaptation.

This post is intended to explore the science and practical application of the interference between strength training and endurance training.

When it comes to bodybuilding and strength related sports, many of us joke that cardio will “steal our gains”. So much so, that we see plenty of bodybuilders boycotting cardiovascular training all together. By the same token, we see this in the endurance world as well. Marathon runners and long-distance cyclists are often “afraid” to add muscle to their frame as their perception is that the added muscle mass will slow them down and thereby interfere with their speed & performance.

Now, as we dive into the data, we’re going to discuss what EACH of these training methods has to offer and how an athlete can better organize their training to benefit from BOTH training modalities with little to no interference.

One of the first researchers to even carry out studies on CT was Hickson in 1980. His findings state that training both strength and endurance simultaneously had detrimental effects on strength development but did not negatively impact aerobics qualities (the endurance work).

After his study, several other researchers were intrigued and began to hypothesize why this may (or may not have) been true. Most recently, there is a wide range of studies that show positive and negative effects of concurrent training. Like everything, we have to take each study with a grain of salt. While labs do their best to control as many factors as possible in their studies, there will always be genetic differences, variations in training times, modalities, nutritional status, etc amongst their subjects. In turn, this can interfere with the results of the study.

Now, what’s come about over the years, is something knowns as the Molecular Signaling Theory. This theory has hypothesized that the specific molecular signaling pathways of strength training vs. the specific molecular signaling pathways of endurance training may in fact inhibit one another.

It’s also important to consider that if an athlete is training intensely in both strength and endurance, we risk the amount of volume and stress leading to overreaching and overtraining as a result of poor or slow recovery.

NOW, PUT YOUR NERD CAPS ON AND LET'S DIG IN!

Muscle fiber hypertrophy, strength, and power acquisition can all be attributed to molecular signaling pathways known as the AKT and mTOR pathways. You’ve probably seen mTOR mentioned before but maybe not the AKT pathway. The mTOR pathway controls the anabolic and catabolic signaling of skeletal muscle mass, resulting in the modulation of muscle hypertrophy and muscle wasting. The AKT pathway plays a key role in cell processes like glucose metabolism, apoptosis (cell death), etc.

Over the years, it has been shown that if your resistance training program elicits a large force output, a good amount of mechanical tension, in addition to muscle damage/cell swelling then hypertrophic pathways (muscle growth) will be activated. Think bodybuilding style training.

However, when we perform long, repetitive, and low intensity muscle contractions (think walking, running, biking, etc), we activate different signaling pathways like AMPK and CaMK which are responsible for endurance based adaptations as opposed to hypertrophic adaptations.

Mitochondrial biogenesis (the growth & division of mitochondria) would be an example of one of these endurance-based pathways. By engaging in endurance training, you’re able to walk, run, bike, etc more efficiently.

So… How does this all relate?

Well, when AMPK (elicited by endurance training) is activated, mTOR pathways (hypertrophy pathways) are suppressed. As a result, our hypertrophic response to resistance training is blunted and by inhibiting mTOR, we can interfere with protein degradation as well.

All of this to say… When performing cardio training during a resistance training program; muscle hypertrophy, strength and power can be compromised.

BUT THAT'S NOT ALL… AND UNFORTUNATELY IT'S NOT THAT EASY!

What’s interesting is that we CAN still see increased endurance performance OR improved resistance training outcomes, even with concurrent training. Which is why there are plenty of studies out there that make arguments against the interference theory.

Some studies even show that resistance training can upregulate AMPK and endurance training can induce mTOR activity. Meaning; if both training modalities are strategically planned out in ones training regimen, there may in fact be a positive effect.

It’s also important to remember however that we can only apply the research under the context of each study. So for instance, if the acute effects of concurrent training were studied, we can’t necessarily apply those same principles to assume chronic adaptations.

For example, we know that new weightlifters get the “newbie gains” effect right? Their muscles adapt much faster than trained athletes when starting a new strength training routine. But eventually, once the gym-goer or athlete becomes acclimated and has some training time under their belt, these “gains” won’t be as “easily” made.

Well, same thing here. If an athlete has no current CT experience, the interference might only occur until they become acclimated. OR the opposite could hold true and an interference may not occur until later in their training cycle. For instance, one study showed that there were no interference effects of CT until the 8th week of training. A time when fatigue may have ensued based on training load, intensity, volume, etc.

Needless to say, this molecular signaling we’re talking about when it comes to CT is highly dependent on the training status of the individual in question (trains vs untrained, strength trained vs endurance trained, training age, etc).

When it comes to prescribing training (maybe you’re a coach) or writing your own programming, the modality, intensity, frequency, and volume of said training can absolutely affect these molecular pathways (as well as protein synthesis). Though, because AMPK down-regulates mTOR (and not the other way around) it is hypothesized that CT can be more detrimental to resistance athletes than to endurance athletes.

SO… WILL CARDIO KILL YOUR CURRENT GAINS OR JUST PREVENT NEW ONES?

To date, there is no conclusive evidence that hypertrophy is blunted when LOW-volume endurance exercise is added into a training program; some studies have even shown it might mitigate muscle loss. On the other hand, HIGH volume endurance exercise CAN be detrimental due to the factors we discussed above.

When it comes to power and strength (as opposed to hypertrophy) Wilson et al (2012) found that power was significantly lowered during CT while muscle cross sectional area and strength was maintained. This suggests that force at high velocities (think vertical jump, not a heavy deadlift) may be affected to a more significant degree with concurrent training than force at lower velocities (like that heavy deadlift). This could be attributed to motor unit recruitment and specific muscle fiber type innervation.

In order to better compliment the demands of strength AND power sports, I’d argue that programming lower volume, higher intensity/velocity work may be more beneficial in terms of maintenance and improvement of power. While the research isn’t conclusive, it’s pretty clear that the intensity and volume of endurance training can affect muscular strength and power.

On the flip side, the amount of volume and frequency endurance athletes undergo in their aerobic training regimens does make is difficult to improve size, strength, and power, especially without taking time away from their endurance recovery. Studies have concluded however, resistance training has positive implications for endurance performance, mainly due to increases in type IIA muscle fibers and a greater potential for force production. This essentially means that endurance athletes that concurrently train can improve their average and peak power outputs (which of course plays a big role in their races!). This study also looked at the effects of concurrent training and found that aerobic performance was increased when combined with strength training as opposed to the group that followed the endurance regimen without strength training.

Needless to say, we shouldn’t overlook the advantageous effects of resistance training for endurance athletes. If you love your running, biking, etc, you should be lifting too!

PRACTICAL APPLICATION

In order to minimize the fatigue and the interference effect, a 24-hour recovery period between training sessions is suggested; the longer the better.

What does this look like for each type of athlete?

Strength and power-based athletes should utilize low to moderate volume endurance exercise in order to attenuate the interference effect while still reaping in the benefits of aerobic exercise.

What if you have to perform your cardio and strength training on the same day?

If resistance training comes before endurance training, performance during the resistance session will hypothetically be higher quality due an absence of fatigue from the endurance training… But hypertrophic signaling will be down-regulated after the endurance session.

If resistance training comes after endurance training, the glucose/substrate depletion and residual fatigue from the endurance exercise would reduce the training quality of the resistance session and may also blunt the hypertrophic response.

So what does this mean for you?

Ultimately, it depends where your priorities lie. Is your main goal to get jacked OR to be the fastest man (or woman) alive? In my opinion, both can’t usually be a priority.

The exercise you perform first is the one you’ll be strongest at. The one you do last is the one you’ll be most fatigued for. If your goal from cardio is simply to get moving, increase blood flow, etc, you’ll still get those same effects after your lift. Ideally, you separate these sessions by day or by a minimum of 3-6 hours. But I understand that multiple sessions per day is not ideal for many people (including myself).

Since most of you on this email list (I’m assuming) are probably here more-so for the muscle gains and not as much the endurance gains, you’re probably not going to want to be fatigued your entire lift just so you can do 20 mins of HIIT on the stair-master. Unless you can keep a few hours (and meals) between sessions, I’d recommend keeping your cardio after your lifting session (and not on a leg day if possible!)

That being said, like all things training and nutrition, you should always do what feels best for you!

RESOURCES