In my opinion definitely not.With good nutrition and not leaving a weight training or kind of (like a functional training) you can maintain the muscle mass

As a triathlete do you want much muscle mass????? You need the power and endurance to do a long distance race but not the mass.

I think the best way to field that question or statement from a client is to avoid getting all “sciency” with your answer. That can be a turn off to someone who has hired you to help them get healthy. (The subject of cardio vs. strength training is not their passion. It’s yours.) Most of my clients need a wake up call when it comes to their fat to muscle ratio, so a simple, “Cardio is going to reduce your overall mass. Period. And it is going to benefit your health and longevity. That’s why we’re here.” I say this to the clients who have hired me to drop weight.

For those who don’t have high body fat percentage and have hired you to change their bodies, another approach would be to design workouts that utilize big general movement, recruiting many muscle groups together. The increased need for blood flow will increase the cardio. I call it “sneaking” cardio into the workouts of my clients who are all about the weights or convinced they will get small if they do cardio.

Another approach would be to say, “Trust me. I know what I’m doing. That’s why you hired me.” And then talk about how you are going to TRACK RESULTS. Body Fat analysis, Circumference measurements, etc. can all demonstrate to a client that they are gaining muscle and assessment is always important to be sure you are both on the right track. This is probably way more than you were looking for when you started this discussion. Oh Well!

As with everything else, moderation and balance is key. Doing a lot of cardio (5-7 times per week for at least 45 minutes each workout) will cause you to become more lean; however, if you pair that cardio with your standard cross training (ie functional strength exercises, weight lifting, etc) as well as other activities you enjoy that require more strength than endurance, you will not “lose” muscle per say. It’s about what you want to focus on and what your primary goal is. If you want to run a marathon, for instance, you will have to primarily focus on distance running; as a result, you lose some weight and become more lean. You may not be able to lift as heavy, but you’ll be able to run much farther and faster. And to compliment your marathon training, you will want to decrease weight and increase repetitions of your resistance exercises. If your goal is to maintain or increase muscle mass, cardio will come second, but still should be an extremely important part of your overall fitness plan. It also comes down to how much time you have to work out and as I stated before, your primary goal will take priority and leave you with less time for other things. So in the end, it really depends on your fitness goals. Achieving that ideal balance between strength and endurance is something many of us seek to achieve, but like anything else, there’s a compromise.

If you can give me more details on what you consider to be “a lot of cardio,” I can probably give you a more specific answer.

Hi Fran,
As you know, the body burns carbs and fat before muscle, so adding protein to the diet is more important with intense cardio exercises (longer than an hour), and the risk of losing muscle mass could only occur if a long list of other factors were combined (for example, too thin, poor food choices, no strengthening routines and so on.)

You could also incorporate weight/resistance training to help prevent muscle loss.

I also think that your long term goals come into play. Are your goals to be a body builder or a distance runner with aspirations for low times for example? They may not be completely compatible.

If you took the offensive line of the Chicago Bears and put them on a marathon training program, would they lose muscle mass? They certainly would, and they may quickly find themselves in wheelchairs.

High levels of muscle mass and high levels of cardio/endurance training are not compatible. This may be partly due to the body’s inability to train intensely for both at the same time. Nevertheless, muscle mass carries with it a metabolic cost. That’s not to say that some athletes cannot be heavily muscled and also do endurance training. However, such athletes would probably be able to maintain greater muscle mass if they did less endurance training.

Beyond the question of muscle mass is that of speed and power. Most sports require speed, agility, power– attributes that are not enhanced through endurance training. Take an athlete who is highly trained, say a world level competitor in the 100m dash, and have him include daily fifteen mile runs in his training. Will he become faster? No. Slower? You bet. Lose muscle mass? Quite certainly.

When Michael Johnson came to the Atlanta Olympic Games in 1996, he carried about twelve pounds more muscle than in 92. Years of intense, explosive, power training built that muscle and increased his sprint speed. He blew away the best sprinters in the world. Had he done a lot of serious endurance training in the four years between Olympic games, he would have not only failed to build that muscle, he probably could not have even qualified for the U.S. team.

Generally speaking, heavily muscled power athletes have a lot of fast twitch muscle fibers, and these fibers do not respond well to endurance training. Is it possible for a sprinter like Johnson to maintain his speed training program while also training for a marathon? Not likely. Such endurance training would cause his sprinting performance to suffer, he would lose muscle mass, he would be a lousy marathoner, and he’d suffer chronic injury.

The average person may well benefit by adding endurance training to his fitness program, and may even increase muscle mass in the process. However, we’re not talking Olympic marathoners, and we’re not talking championship bodybuilding or NFL football. The training needs and results of the average person are vastly different from those of elite athletes. The answer to the question, “If I do a lot of cardio work, will I lose muscle”, depends a whole lot on who the “I” is.

I would agree with most posters. I think it depends on a number o things including how much strength training your doing and what type of cardio you are doing. CrossFit workouts task you both physically and cardiovascularly. I still run as part of my training, but I am a big believer in interval training whether that be sprints with jogging, or running hills, or biking hills. I compete in both adventure races and CrossFit competitions and am focused on both maintaining my muscle mass as well as improving my cardio performance.

Right on Kevin. If muscle retention is important then high intensity intervals aesthetically way to go. Steady Cardio does use more muscle as fuel.

The question is: how much muscle mass do you have now? As an exercise physiologist, I can tell you that research shows endurance-only training does not build or maintain muscle like strength or sprint training do. Triathlon training will certainly prevent the kind of muscle loss (atrophy) that most sedentary people experience as they age. However, it’s a good idea to engage in some strength training — more during the off-season — to build and maintain your strength. For longer-distance triathlon, you don’t want excessive bulk, so strength train with moderate weights (10-15 reps max) and only 1-2 sets per exercise, unless you are trying to build strength in a weak muscle (then do 3 sets).

You won’t lose muscle if you eat and train correctly. People are amazed at how I was able to lose over 100 lbs without excessive skin. I did it gradually over three years doing Formula 55 high intensity interval training app. I prefer using the treadmill and stair mill with a 20 lbs weighted vest. Please note that nutrition is very important

@Mike P, could you elaborate more on your research?

@ the group, two questions, how to lose fat, not too much muscle and find ideal weight for sprint TRIs?
AND book/study recommendations on the SCIENCE of diet and endurance training?

side note
I have found that I have a great structural frame and bone/muscle density and it is easy to strength train all year round. My ligaments create a difficult challenge.
I am 5′ 9″, size 10, I guess I could leave the poundage out of this one for now. I have high muscle weight but too much fat. I find the muscle is helping me burn the fat, however, I find that the weight in general slows me down in my training. (I run 2-3 5k each week, w/circuit training, swimming)

My overall goal is to lose the fat altogether and be strong and fit enough for sprint tri’s without being too heavy in muscle. I have to admit, I am an exercise, boxing, weight/circuit training addict. I want to get back into Yoga for many reasons but hate aerobics, group/cardio classes. Still looking for a solo Yoga program that i really like. Broken tailbone so Pilates is out.

I don’t know how to find balance and HAVE NOT figured out the SCIENCE of eating which is SO important. I still have yet to find a book or recommendation for the very book that would educate me on the science of how to fuel my body properly.

It can happen with excessive amounts of cardio, but like Avaneil says, cardio can help maintain muscle, increase your fitness to be able to push harder in your resistance sessions, and the main way you’ll lose muscle is if you’re in a severe calorie deficit for too long.
In my experience, you need to be doing a lot of cardio and running on empty to lose muscle. Ideally keep your weights and cardio sessions separate if you can, eat protein before and after your workouts and make sure you are eating the right macro-nutrients (protein, carbs, fats).

Sounds like we have hit this one on the head taking everyone’s opinion into account however – I would like to throw this one into the mix….body type! Your typical Ecto that has majority slow twitch fibres will certainly lose muscle tissue quicky when doing long bouts of cardio despite calorie intake as opposed to meso & endo’s that will lose very little with cardio so long as they keep up good nutritional consumption.

When working on strength or hypertrophy I keep the heart rate below 70% of maximum according to the Karvonen formula. So aerobic exercise is still a part of the program and you can do as much as you want but don’t exceed the 70% heart rate.