The Hybrid Athlete’s Quick and Dirty Guide to Interference Effect

"Hybrid Training" is a big trend right now, and despite the corny name, the idea that people don't have to choose between either improving their strength or improving their endurance entering mainstream fitness is a pretty cool shift. 

I think the main reason why people are so drawn to the idea of hybrid training is that strength and endurance seem to be on opposite ends of the spectrum. The popular view is that you need to get big and bulky to be strong, and you need to be thin and wiry to have good endurance - so trying to do both at the same time must result in less progress than just training for either strength or endurance in isolation, right?

What is “Hybrid” Training?

“Hybrid” training just means simultaneously training for strength and endurance throughout a training program.

While “hybrid” training is the hot thing to call it right now, researchers have been calling it “concurrent training” for many, many years while it has been a heavily studied topic - specifically how strength and endurance adaptations may help or hinder one another.

What is the Interference Effect?

The interference effect is the idea that training for strength and endurance at the same time causes adaptations in one to blunt adaptations in the other - either endurance blunting strength or vice-versa.   

On the surface, this looks like it would be the main challenge with a hybrid approach to training, and a large part of why a lot of people find it impressive to see a person who’s both big and strong with great endurance.  But it doesn't seem to be as big of a problem as you may think. 

Should “Hybrid Athletes” Worry About the Interference Effect?

Well... both yes and no. Like most things human-body related, the answer to this question isn’t black and white (but it’s definitely made out to be that way by the average online meathead). 

A great review by Dr. Methinitis [1] at the University of Athens goes over a lot of the key points about the interference effect, and the nuances behind how much and when you should worry about it. I’d highly recommend reading the whole thing, but I promised “quick and dirty” so here were my main takeaways: 

1) Overall training load and overall fatigue can be a sort  of “interference” between endurance and strength training.

Strength training takes a lot of work. Endurance training also takes a lot of work. If you try to push everything to the limit all at once, it’s more likely that you’ll be giving your body more overall training than what it can recover and adapt from.

So in this sense, the interference effect can be true - but in a similar way that doing too much of any kind of training will result in poor adaptation and performance.

2) On the aerobic/endurance side of things it seems like you don’t have much to worry about at all.

When overall fatigue is managed properly, strength training doesn’t seem to have negative effects on endurance performance, and many studies even show better endurance gains from “hybrid” or concurrent training compared to only doing endurance training by itself [1].

3) Endurance training has the potential to negatively affect resistance training adaptation - mostly in specific cases, and it’s relatively easy to avoid.  

The potential for some concern is in the other direction - looking at the effects of endurance training on strength and muscle building adaptation.

Long duration, moderate intensity, continuous endurance training (like a long run) has been shown to blunt the muscle building response to a strength training session at the cellular level (via AMPk signaling inhibiting the mTOR pathway, and some other nerdy and interesting stuff that you can read about in the article by Dr. Methinitis) [1].

The interesting thing is that this interference is not seen with all forms of endurance training. Depending on how you structure your training, it seems as though you can pretty much entirely avoid the interference effect altogether, and make both strength and endurance gains at the same time [1]. Have your cake and eat it too. 

How Can You Avoid the Interference Effect?

1) Use high intensity, low volume forms of endurance training when possible.

It seems that shorter duration, maximal effort, high intensity endurance training (think HIIT training) has no negative impact on muscle building, strength, or muscular power adaptations as part of a hybrid program, and will still meaningfully help you build better endurance. Some studies even showed a better response to resistance training when doing this type of aerobic work [1].

2) Use cycling if possible.

Cycling interventions seem to reliably cause less interference when used in studies compared to running [1]. So if you’re not married to any one mode of cardio (i.e. if you’re not a runner) cycling might be a solid choice.

Even if you are a runner - using cycling during your off season during more strength and hypertrophy centered periods of training could be a good way to maintain your endurance while avoiding interference with your sweet, sweet strength training gainz. 

3) Split your endurance and strength work in separate sessions, ideally 24-48 hours apart.

48 hours seems to be on the safer side for preventing interference, especially when doing an endurance session before a strength session [1]. While it’s not always possible to have a full 2 days in between, the closer you can get the better. 

4) Whichever adaptation is your priority should be trained first, and more often.

If your main goal is getting stronger or building muscle, then your resistance training should happen first when you have more resources to spend on training and recovering. The review author [1] recommends a ratio of 2:1 or 3:1 between resistance training sessions to endurance sessions per week (and anecdotally, this has worked very well in my own experience also). 

If your main goal is building endurance, then your endurance training should happen first. The review author [1] recommends a ratio of 1:1 or 1:2 of resistance training to endurance training in this case - which also seems to be spot on for most people in my experience.

5) Consider your overall training volume, and be gradual.

Big spikes in the amount of training you are doing are never a great idea - but especially with concurrent training where excessive training can lead to a sort of “interference” in itself. Remember that the main goal of training is to adapt, not to beat yourself up. Take things gradually, start easy, and incrementally increase your endurance and strength training over time. 

It may also be useful to alternate periods of time where your focus shifts more towards either endurance or strength/hypertrophy to keep overall training load within a range you can fully recover and adapt from. 

To Wrap It Up…

Again - corny name, but I’m overall a huge fan of the “hybrid training” approach getting more and more popular. It’s always cool to see people breaking away from the crusty old ideas that you have to pick either endurance or strength and never both. While the interference effect should be taken into consideration when planning concurrent training, a little bit of knowledge and a few small tweaks to a training plan can turn it from a full on roadblock to an easily avoidable pothole - and help you keep discovering all the cool things your body is capable of.

I really enjoy working with my 'hybrid' clients - we've had a lot of great success, and they're always down to get in the details and put in the work. If you have questions about hybrid training, how to balance demands of endurance and strength, or anything else - feel free to reach out here. You can also check out different options to work with me as your coach here. 

Now get out there and simultaneously make some strength and endurance gainz.  

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References:

[1] Methenitis, S. (2018) ‘A brief review on concurrent training: From laboratory to the Field’, Sports, 6(4), p. 127. doi:10.3390/sports6040127.