Some say that concurrent training is bad for muscle growth. If you want to build muscle as fast as humanly possible, endurance training should be kept to an absolute minimum.
How much cardio, if any, should you do when you’re trying to build muscle? At what point does concurrent training start interfering with muscle growth?
Is Concurrent Training Bad For Muscle Growth?
Concurrent training certainly has the potential to put the brakes on muscle growth.
However, the extent to which concurrent training affects your ability to build muscle depends on a number of factors, including:
- How much weight training are you doing?
- How much endurance training are you doing?
- How hard is that endurance training?
- What type of endurance training are you doing?
- When is that endurance training performed?
It is possible to train for both muscle growth and endurance at the same time, just as long as your overall training program is set up properly.
That is, if you’re trying to build muscle as fast as possible, you can still do some endurance training at the same time without slowing your gains.
Concurrent Training: The Interference Effect
Much of the concern about concurrent training interfering with muscle growth started back in the 1970s, when a powerlifter by the name of Robert Hickson decided to join his boss Professor John Holloszy, the father of endurance exercise research, for a regular afternoon run.
However, despite the fact he was still doing the same amount of weight training, Hickson found that his muscles were shrinking and he was getting weaker.
When Hickson told his boss what was going on, Holloszy told him that “this should be the first study you do when you have your own lab.”
When Hickson opened a new laboratory at the University of Illinois, that was exactly what he did.
In his study, Hickson found that subjects who combined resistance and endurance training made smaller strength gains than those who lifted weights and nothing else [1].
When others replicated Hickson’s study, they found similar results.
Training for both strength and endurance, termed concurrent training, led to reduced gains in strength and size, a phenomenon dubbed the “interference effect.”
Do Endurance and Strength Training Mix?
Does this mean you should ditch endurance training altogether if you want to gain muscle as fast as humanly possible?
No it doesn’t, and here’s why.
First, Hickson had his subjects lift weights five days a week and go running or cycling six days a week. That’s a lot of concurrent training, and far more than most people are doing. Even then, the interference effect didn’t show up until seven weeks into the study.
What’s more, the training program Hickson devised was not for the faint of heart. The legs were trained five days a week with deadlifts, squats, leg presses, leg curls, leg extensions and calf raises, for a total of more than 40 work sets per week.
The endurance training side of things was equally brutal. It involved interval training (a total of six 5-minute bouts at a work rate approaching VO2max, with each bout separated by two minutes of rest) on an exercise bike, three times a week.
On the other three days, subjects were told to run “as fast as possible” for 30-40 minutes.
There were no recovery days. No easy weeks. It was pretty much flat out for the entire 10-week study.
But even then, strength in the concurrent training and resistance-only groups increased at much the same rate during the first 6–7 weeks of the study.
While the resistance-only group carried on getting stronger, gains in the concurrent training group hit a plateau, before taking a dip in weeks 9 and 10.
All of which brings me to the first factor you need to consider when planning your concurrent training program: How much endurance training are you planning to do?
Endurance Training Volume
Any negative effect that concurrent training has on your gains will depend on the amount of endurance work you’re actually doing.
Lifting weights five days a week and doing cardio six times a week, as Hickson’s study involved, will make it very difficult to recover and grow.
But if all you’re doing is a couple of hours a week of moderate-intensity cardio, you’ll be far less likely to run into problems.
The extent to which concurrent training interferes with your gains is also, for the most part, body part specific.
Doing high-intensity interval training (HIIT) before lifting weights, for example, has been shown to slow size and strength gains in the lower body [2]. But it didn’t hamper gains in the upper body.
You also need to consider the length of time between endurance training and weight training.
On one end of the spectrum, you can do cardio and weights back to back, with little or no gap between the two. Or you can go to the other extreme, and do them on separate days.
Which approach works best?
In most cases, you’re better off keeping endurance and weight training separate. Inserting a sufficient length of time between the two can limit the extent to which endurance exercise interferes with your gains.
When US researchers looked at the research on concurrent training, they came to the conclusion that, in an ideal world, endurance training and weights should be separated by anywhere between six and 24 hours [3].
However, I don’t live in an ideal world, and neither do you. It might be the case that the only time you can fit in cardio is to do it before or after you lift weights.
If so, what should come first, cardio or weights?
Probably the worst option is to do endurance training right before you lift. A bout of interval training performed immediately before strength training, for example, has been shown to blunt gains in muscle mass [4].
Ten or 20 minutes of gentle warming up on the bike, treadmill or rowing machine is fine. But a hard bout of cardio is going to leave you fatigued before you even start lifting weights. This in turn is going to make it harder to do the work necessary to stimulate muscle growth.
Exercise Type
You also need to think about the type of endurance training you’re planning to do.
As part of a concurrent training program, research shows that running is much more likely to impede recovery and interfere with your gains [4].
That’s not to say you have to avoid running completely. But if you want to minimize the risk of concurrent training hurting your gains, something low impact like rowing, incline treadmill walking, swimming or cycling would all be better alternatives.
In fact, cycling may well be the ideal companion to resistance training.
In one study, adding 30-60 minutes of cycling twice a week to a two-day strength training program had no negative effect on gains in muscle size or strength [5]. The thigh muscles grew at a similar rate in both the strength-only and concurrent training groups.
More interesting still, there is some research to hint at the possibility of a faster rate of muscle growth with cycling and resistance training compared with resistance training alone [6].
Granted, the research was done on resistance-training newbies, where virtually any stimulus will stimulate growth. And the total amount of training they did was relatively low.
But, at the very least, the findings do suggest that concerns about concurrent training interfering with muscle growth, provided your training program is set up properly, are overblown.
Concurrent Training, Age and Stress
Your ability to recover from and adapt to a concurrent training program is also going to be heavily influenced by your age.
As you get older, you’ll notice that your ability to recover from one training session to the next is not what it once was. A concurrent training program you thrived on in your twenties may well prove to be too much for your body to handle at the age of 40 or 50.
In one study, a group of triathletes in their fifties recovered more slowly than triathletes in their twenties in the days following a 30-minute downhill run [6].
The synthesis of new muscle protein was reduced, contributing to a slower rate of muscle repair. There was also a trend for masters triathletes to turn in a slower time trial performance than their younger counterparts ten hours after the run.
Something else to consider is anything you might have going on that’s causing you an undue amount of anxiety, worry or some other form of psychological stress you don’t want to feel.
Physical and psychological stress make withdrawals from the same account, and too much of one can make it harder to recover from the other.
As a result, you’re not going to recover as well from workout to workout, and the adaptive response to your training program won’t be all that it might have been.
There are no set rules dictating exactly how much training you can and can’t handle at a given age. Instead, I think you’re much better off relying on your performance in the gym to tell you if what you’re doing is too much, too little or about right.
One method I use to gauge how well I’m recovering from one workout to the next is to track my performance in the gym.
And by performance, I’m talking about the number of reps I’m able to do with a given amount of weight, which I’m defining here as repetition strength.
If my repetition strength is declining from one workout to the next, that’s a sign I’m doing too much and need to cut back.
Don’t pay too much attention to what happens in a single workout. Sometimes your performance can take a dip for reasons that have nothing to do with your training program.
You may have been having a bad day caused by lack of sleep, poor diet, psychological stress, or some combination of the three.
But a bad couple of weeks, or even just one very bad week, is a sign you may be overdoing it, and need to cut back.
Something else to consider is how you’re feeling. Do you actually want to go to the gym? Or is your energy and enthusiasm for training lower than normal?
If your desire and motivation to train is low, and your performance in the gym is getting worse rather than better, then some aspect of your concurrent training program needs to change.