Q: I've heard that doing cardio will keep me from gaining muscle. True?
—Chris G., Effingham, IL

A: It depends.

(By the way, you’ll find that most of my responses will begin with "it depends", since there are few training issues that are cut ‘n’ dry absolutes.)

Performing “cardio” too frequently, too intensely, or for too long can certainly prevent you from gaining muscle from your strength training workouts.

Consider all the necessary resources required by your body to build muscle. You need good nutrition to provide protein for muscle growth, and carbohydrates and fats to fuel and enhance recovery from your intense workouts. You also need rest and recovery time between workouts to allow your body to rebuild and increase your muscle mass. Read: You don’t grow muscle during your workout, but rather between workouts.

Now imagine all of these resources as a bucket of water: the more often the bucket is full, the faster your ability to make gains in muscle mass. The emptier the bucket becomes, the harder it is to build more muscle.

Of course, for every gut-busting strength training workout you perform, you take a scoop of water out of the bucket. And the harder you train, the bigger the scoop of water you take from the bucket. As you replenish your muscle-building and energy supplies by resting and eating effectively, you assure that you have all the necessary resources necessary to build muscle. In other words, you refill the bucket.

The problem with doing any random form of cardio is that you draw on the same resources that you have available to build muscle. In other words, you take more scoops out of your bucket. That not only means fewer resources that are available for building muscle, but because your recovery is also compromised, it becomes even HARDER to refill the bucket.

That doesn’t mean you can’t do any cardio during a muscle building phase. It just means that you need to perform cardio that minimally impacts the resources necessary to build muscle. Or even better, do a form of cardio that has the ability to ENHANCE your muscle-building phase.

Let’s take a quick look at the most common types of cardio. This will help you understand what to include and what to avoid.

1. Recuperation/Recovery

Adding this form of cardio enhances blood flow to your working muscles and can actually improve your recovery from other forms of exercise like strength training. You need to be specific to the muscles involved. So if you work your lower body hard on Monday, you could do a lower body recovery workout on Tuesday. This consists of continuous activity like cycling, stair climbing, walking, or jogging.

Your objective: Keep your heart rate between 100 and 120 beats per minute (bpm) to avoid taking a big scoop out of your recovery bucket. Perform this workout one or two times per week for 15 to 20 minutes. You can do it on off days or after your strength training workouts.

Intensity and volume are both pretty low, so this type of interval won’t impact your muscle growth or strength at all.

2. Cardiac Output Development (COD)

This form of cardio is one step up the intensity ladder from Recuperation/Recovery Cardio. The goal here is to actually increase the size of your left ventricle—the chamber of  your heart that pumps blood to the rest of the body. The cool thing about COD is that by making the left ventricle bigger, your overall resting heart rate decreases. This means that you'll return to your resting heart rate levels faster after you workout. The faster your heart rate slows back to resting levels, the calmer your nervous system and the faster you recover for your next workout.

Keep you heart rate between 120 and 140 beats per minute (bpm) to avoid taking a big scoop out of your recovery bucket. Perform this one or two times per week for 30 minutes. If you’re an athlete with a resting heart rate that's over 65 bpm, you may need to increase this to 60 minutes if your resting heart rate is over 65 bpm.

Intensity is still very low. So if you stay on the low end of the duration recommendation a couple times a week, it won’t impact your ability to build muscle. If you’re an athlete and need to hit the high end of the duration recommendation, it may slow muscle growth to a slight degree, but the trade off in endurance potential is worth it. Once your resting heart rate reaches the desired level, perform maintenance once or twice a week at 30 minutes. If your schedule allows, perform COD on off days from strength training. (However, if you can't spare an extra day, you do this cardio workout immediately after you strength train.) ALSO: If you’re performing COD at the higher end of the duration zone, then don't worry about doing recovery/recuperation cardio. If you’re only performing short COD workouts a couple times per week, one or two recovery/recuperation workouts may also be beneficial.

3. Alactic Intervals

This form of interval training targets fast-twitch muscle fibers. For this, you'll do exercises that are hard and fast, like repetitive jumping exercises, medicine ball throws, and short sprints. Sets last about 10 to 15 seconds, much like a maximal set of bench presses or squats. So these are a very solid complement to heavy strength work—as long as you keep the total sets in check.

Simply perform sets of 10 to 15 seconds as hard as possible, and then rest five times longer than the set took. So you’re on a 1:5 work to rest ratio.

Here’s a common routine we use at my gym, Indianapolis Fitness and Sports Training (IFAST). Because of the explosive nature of these intervals, you’ll usually want to place them early in your workout—before your regular strength training.

Do 10 seconds of kettlebell jumps, followed by 50 seconds of rest. That's one set. Do a total of 8 to 10 sets. To perform a kettlebell jump, hold a 16 to 24 kg kettlebell at arms' length down by your waist. Squat down and jump as high as possible (don't swing the dumbbell), land softly, and then repeat.

That’s only 80 to 100 seconds of work. So the impact on your muscle growth is practically nil, but the benefit is an improved capacity to perform more heavy training.

After your alactic intervals, perform some active recovery like the recuperation/recovery method above for 8to 10 minutes before starting any other form of training (such as your strength workout). This gives your fast-twitch fibers a brief and effective recovery period to assure you’re functioning at full force.

Now if you’d really like to kick it up a notch, perform this 40 to 50 minute cardio “series” on an off day from strength training.

*Do 10 seconds of kettlebell jumps followed by 50 seconds of rest for 8 to 10 sets.
*Do 8 to 10 minutes of active recovery
*Do 10 seconds of kettlebell jumps followed by 50 seconds of rest for 8 to 10 sets.
*Do 8 to 10 minutes of active recovery
*Do 10 seconds of kettlebell jumps followed by 50 seconds of rest for 8 to 10 sets.

One caveat: Keep your heart rate under 165 to 170 bpm to avoid too much stress, which will impact your ability to build muscle.  If you find that you can’t get your heart rate down to about 130 bpm by the end of your rest period and/or your heart rate shoots well over 170 bpm, you’re done for the day.

4. Aerobic or Anaerobic Interval Training (a.k.a. High Intensity Interval Training)

This type of  cardio represents your most intense variations of conditioning exercises. These are longer, harder sprints—that you do by running or cycling on an exercise bike—followed by a rest period equal to two or three times the work interval. They typically look something like this:

*Sprint as hard as you can for 30 seconds
*Rest for 90 seconds
*Sprint as hard as you can for 30 seconds
*Rest for 90 seconds
*Sprint as hard as you can for 30 seconds
*Rest until your heart rate returns to normal.

That's one set of 3 reps. Try working your way up to 3 sets of 5 reps.

You’ll typically experience that all too familiar “burn” in the muscles that you’re using. That means you're doing it right.

These intervals are GREAT FOR FAT LOSS, but LOUSY FOR MUSCLE BUILDING. This type of training will take the biggest scoops of water out of your “energy bucket” and in doing so, steals resources like energy and protein that you need to build muscle. It also prevents you from recovering effectively before your next workout. Therefore, if you're really focused on packing on muscle, this type of cardio should be used sparingly (once every couple weeks) or not at all. Save it for when you’re trying to get lean for summer or a beach vacation.