Building muscle is the end-all-be-all for many trainees — and why shouldn’t it be? After all, there’s been a proven link between lean muscle development and strength.
Working towards a lean, muscular, and athletic physique — even with a personal trainer — isn’t easy for everybody — especially without drugs or fortunate genetics. It costs time and calories. This is why it isn’t uncommon to hear the age-old consensus of conditioning being at odds with hypertrophy.
Does cardio burn muscle, as thought by many? The answer is that it depends on your circumstances.
For starters, cardio can mean a lot of things. Cardiovascular conditioning modalities (i.e., “cardio exercises”) aren’t all the same. Some are conducive to gaining size while others do indeed destroy some of that hard-earned muscle built under the iron.
In this post, we weigh in on this question. Read on to the very end to see how cardio can kill gains and how it might also be useful when you’re trying to get swole.
AMPK, mTOR, and a Metabolic Game of Tug-of-war
Whenever people talk about metabolism, the conversation usually begins and ends with “burning” or “using” energy. While this isn’t inaccurate, it’s incomplete. The truth is that metabolism involves two processes.
One metabolic process uses nutrients, oxygen, and even tissues (like fat and muscle) for energy. This is catabolism.
The other side of metabolism uses energy and shuttles them to new tissues like muscles. This is anabolism.
Metabolism encompasses these two processes. Why is this important? The presence of two metabolic processes allows the body to use energy from food in different ways. Unfortunately, these processes don’t occur at the same time. In fact, for one to take place, the other needs to take a back seat.
It all has to do with the chemicals needed for the processes to occur. For one, there’s catabolism-inducing AMPK (or AMP-activated protein kinase). On the other end of the metabolic tug-of-war rope is muscle-building mTOR, meaning mammalian target of rapamycin. Let’s get into what these enzymes are:
AMPK — Necessary To “Go”
When it’s go-time, the body takes energy from wherever it can. To do this, the body needs to secrete AMPK to call the body’s energy systems to replenish lost energy.
AMPK floods the system in the presence of a stressor. Whatever the stressor is, it has to be stressful enough to deplete the body’s energy stores. AMPK helps the body regulate energy by helping it stay balanced. It does this by telling the body to burn energy and nutrients. In the absence of energy and nutrients, AMPK will signal the burning of something else — tissues.
Is this a bad thing? Well, it depends on the trainee’s goals. One of the tissues that can end up in the metabolic furnace is adipose tissue, best known as fat. Nobody will disagree that fat-burning is a bad thing.
However, when a stressful activity or exercise goes on for too long, the body will draw energy from muscle. This is the last resort, but when there aren’t enough fat stores and calories, muscle degradation can occur. This is what nobody who’s serious about gains wants.
Certain activities can trigger a release of AMPK. When it comes to physical activity, no other form of exercise causes an AMPK spike more than long-duration cardio. For anyone who needs proof, all that’s necessary is to compare the physique of a long-distance marathon runner and a powerlifter.
The marathon runner maintains movements at a low intensity to sustain a 20-kilometer run. The powerlifter needs energy for just one maximum-effort rep and to maintain the musculature to do so.
AMPK is necessary for the body to pool energy stores for long-duration runs or “cardio.” Because burning energy and using energy to build tissue isn’t possible at the same time, cardio exercises done at high intensity for a long time will inhibit muscle-building.
mTOR — What Tells Muscles to Grow
If AMPK uses tissues and calories for long-duration cardio activities, mTOR tells the body to rebuild tissue. mTOR is also an enzyme that circulates the body to signal anabolic pathways. Anabolic pathways create a cascade of chemical responses that lead to gains in muscle size.
mTOR makes growth possible in mammals — including humans. A surplus of it leads to growth in certain parts of the body, namely the skeleton and muscles.
mTOR activation takes place shortly after a workout. But for it to work its magic, one hormone needs to spike — insulin. Insulin shuttles glucose to muscle cells for them to regenerate. The regeneration of muscle cells leads to larger muscle tissues — hence, gains.
mTOR signals the body to use energy to rebuild muscles, but this is only possible with a surplus of calories and energy. As mentioned earlier, AMPK tells the body to take energy and use it immediately for an energy-sapping activity like long-duration cardio.
This is why intense long-duration cardio isn’t advisable for trainees looking to fill out shirts or their weight class nicely.
Should a Muscle-Building Program Have Zero Cardio in It?
When we talk about cardio in its extreme form — which is long-duration steady-state exercise — then the answer might just be yes. However, there’s a caveat to this.
Not all cardiovascular exercises need to be lengthy and low in intensity. Muscle-building is achievable even in the presence of cardio, but cardio needs to be the focal point of careful programming on the part of the personal trainer.
By doing cardio workouts that are moderate in intensity and short, trainees can retain (and even build) muscles. On top of that, there’s always a place for elevating one’s heart rate for health benefits.
Cardio at the right dose can also help trainees cut body fat leading up to a competition. Also, because cardio workouts like HIIT or long walks improve circulation, muscles can recover faster due to a higher blood supply.
So- Does cardio kill gains? In short, cardio can hinder your gains, but it doesn’t need to. All trainees need to do is fine-tune cardio and make it fit into a program.
How? We talk about this in the next section.
Cardio Without Muscle Loss: Practical Recommendations
Genetics can play a factor in the kind of cardio protocol performed. Also, the presence of performance-enhancing drugs can help trainees tolerate additional cardio work.
For the natural, drug-free trainee, here are some ways to work cardio into a muscle-building program.
Keep Cardio Workouts Short But Intense
Keep in mind that an element of AMPK secretion is prolonged stress in the form of cardiovascular exercise. By making workouts shorter but intense, trainees can reap the heart-pumping benefits of cardiovascular exercise in half the time or less without sacrificing the release of mTOR.
This is why high-intensity interval training (HIIT) is best for trainees looking to retain their buns and guns. HIIT workouts result in nearly the same workload as a long-distance run. Taking no more than 15 minutes, the workload and benefits stay the same without the catabolic effects.
Go Long But Extremely Low-intensity
It’s still possible to do long-duration cardio on a muscle-building program. Of course, when time increases, intensity needs to drop — significantly, at that. Long-duration leisurely cardio doesn’t need to be complicated. The perfect example is an exercise that requires no coaching but requires a lot of patience — walking.
Eat at a Surplus
The muscle-building effects of mTOR occur when there are enough calories to burn. As training volume increases to accommodate both cardio and muscle-building, a trainee needs to consume more calories.
Do Weight Training and Cardio on Separate Days
Above-average genetics and a high level of conditioning can allow a trainee to train muscles and the cardiovascular system on the same day. For everyone else, it’s better to have weight training and cardio on separate days. Most studies confirm that 24 hours between strength and cardio workouts are sufficient.
Of course, as mentioned earlier, the cardiovascular work needs to be either short but intense or long but easy.
Cardio Doesn’t Need to Get in the Way of Getting Bigger
When it comes to planning training, the goal is to add the least possible volume to get the most results. This is especially true for adding cardio to your program.
DIY-ing your programming is fine, but mistakes will happen, and they’ll stall your progress. If you’re serious about gaining muscle and maintaining a lean physique, you need a personal trainer to optimize your training.
Try a free week with us and experience cardio and muscle-building programming backed by science and experience.