If you’re on the journey to build muscle and transform your physique you’ll no doubt be following Brad Schoenfeld’s M.A.X Muscle Plan.

The plan takes you through everything you need to build muscle, with a variety of strength training exercises for each part of the body, plus nutrition advice.

But, can you add cardio to your muscle-building regime? Or will it hinder your progress? We explore in this adapted excerpt from Brad Schoenfeld’s The M.A.X Muscle Plan 2.0.

Pros of cardio for optimising body composition

Fat loss

When evaluating the relevance of cardiovascular exercise from a hypertrophy standpoint, we must consider the principle of specificity. The principle of specificity states that adaptations are specific to the type of training you perform. With respect to cardio, several associated adaptations can have a beneficial effect on body composition. For one, cardio helps expand your network of capillaries (1) —the tiny blood vessels that allow nutrient exchange between body tissues. Although resistance training alone does promote capillarization, the extent of these increases is limited; only by adding cardio to the mix can you optimally enhance angiogenic adaptations (2).

Capillary increases have particular relevance to fat loss. You see, before body fat can be metabolized, it must first enter the bloodstream and then be transported to the active tissues for use as fuel. Unfortunately, blood flow tends to be poor in fatty areas, which inhibits your body’s ability to harness fat from these regions. The more capillaries you have, the more efficient your body becomes at liberating and using fat, particularly from stubborn areas. To this point, fat loss from cardio exercise seems to preferentially come from the midsection, irrespective of dietary factors.

Active recovery

Cardio serves as a form of active recovery. During aerobic training, blood is shunted to the working muscles. This further enhances nutrient delivery and facilitates the removal of metabolic by-products; it’s why muscle soreness tends to dissipate more quickly after performing a bout of light cardio. The catch is that responses are muscle specific. If you perform only lower-body cardio, you’ll see the majority of recovery-related benefits in your legs. To realize results in the upper body, you need to perform upper-body cardio exercises.

Cons of cardio for optimising body composition

The interference phenomenon

The problem with concurrent training is that adaptations associated with resistance training aren’t necessarily compatible with those of aerobic exercise. Each type of training regimen activates and suppresses specific genes and signaling pathways, and these pathways tend to interfere with one another. The net result is an impaired adaptive response, particularly from a muscle hypertrophy standpoint; cardio seems to impair resistance training adaptations more than vice versa.

AMPK is generally considered a primary culprit in the interference phenomenon. AMPK is associated with an energy-conserving pathway that regulates adenosine triphosphate (ATP), the high-energy compound that fuels all human work. When energy levels become depleted during aerobic exercise, AMPK turns on enzymes involved in carbohydrate and fatty acid metabolism to restore ATP levels. Among other things, this increases the use of fat as a fuel source.

That’s the good news.

The bad news is that AMPK activation also blocks an anabolic signaling enzyme called mammalian target of rapamycin (mTOR), which is critical for carrying out muscle protein synthesis. This makes biological sense because the body uses a lot of energy to make muscle proteins, and conserving energy becomes essential to survival during times when ATP levels are low. The interference effects of AMPK on anabolic processes were demonstrated in an elegant study whereby researchers electrically stimulated the hind limb muscles of rats with either long-duration, low frequencies (to simulate aerobic exercise) or short-duration, high frequencies (to simulate resistance training) (1). Results showed that low-frequency stimulation ramped up AMPK whereas high-frequency stimulation activated PKB, an anabolic signaling enzyme. The researchers thus termed the phenomenon the AMPK-PKB switch, which proposes that aerobic and anaerobic exercise produce opposing signaling responses that are incompatible for optimizing muscular adaptations.

Overtraining

Remember that everyone has an upper limit to how much exercise they can tolerate before overtraining sets in. Performing cardio adds to the total amount of exercise-related stress placed on your body. These stresses can overwhelm your capacity to recover, ultimately leading to an overtrained state. Overtraining is associated with heightened fatigue, reduced testosterone levels, increased cortisol levels (a catabolic stress hormone), and an impaired immune response. To say the least, these factors are not conducive to gaining muscle.

Integrating cardio into the M.A.X Muscle Plan

If you want to incorporate cardio, the routine must be carefully structured to complement the resistance-training element of the M.A.X. Muscle Plan. Cardio has three distinct variables: intensity, volume (combination of duration and frequency), and mode.

Intensity

Intensity refers to how hard you train. You can estimate aerobic training intensity in several ways. The most popular method involves taking a percentage of maximal heart rate (MHR), which is calculated by subtracting your age from 220. For example, if you are 30 years old, your maximal heart rate is 190 (220 – 30 = 190). To determine training intensity, simply multiply this number by a given percentage based on how hard you want to exercise. So let’s say you want to perform steady-state cardio at 60 percent max heart rate (a relatively low intensity). Using the previously calculated max heart rate of 190 as an example, your target heart rate would be 114 beats per minute. It’s that easy. I’ll note that the formula is a bit of an oversimplification because the relationship between max heart rate and age is not necessarily linear and appears to be influenced by fitness level. More detail is beyond the scope of this book, and the stated max heart rate formula is sufficient for our purposes.

Aerobic intensity exists on a continuum, with slow walking at one end of the spectrum and an all-out sprint at the opposite end. A strategy called high-intensity interval training (HIIT) incorporates a combination of intensities whereby relatively short bursts of high-intensity aerobic activity are interspersed with periods of low-intensity activity. Examples include alternating periods of running and walking or sprint cycling and easy pedaling; however, any cardio modality can be employed provided it allows the ability to train at varying aerobic intensities.

If you’re new to resistance training, adding a cardio component can actually enhance muscle growth; the caveat is that aerobic intensity must be relatively high to achieve results.

Volume

Volume of aerobic exercise should be considered on a weekly basis. In this regard, volume represents a combination of aerobic duration and frequency. Duration refers to how long you train. As a general rule, duration is inversely related to intensity; you can go longer if you don’t train as hard. Frequency refers to how often you train. Frequency is generally expressed in terms of the number of weekly aerobic sessions (although technically you could perform multiple sessions in the same day). Thus, volume is calculated as the product of duration and frequency.

Volume may have the greatest influence on the hypertrophic interference associated with concurrent training. When combined with intense lifting sessions, long, frequent aerobic bouts can give rise to a catabolic hormonal environment and chronic muscle glycogen depletion, hastening the onset of overtraining (3).

Mode

Generally speaking, you should choose a modality based on preference. The most important factor in getting results is adherence, and if you like the cardio modality, you’ll be more inclined to stick with it over time. That said, there are considerations that should be taken into account from a cost–benefit perspective. Most specifically, some research indicates that running may be especially detrimental to muscle growth when performed in combination with resistance exercise (4). It is speculated that running-related impairments to hypertrophy may be related to excessive muscle damage caused by higher associated eccentric forces compared to other modes. Conceivably, high levels of damage could interfere with post-exercise recovery and thus blunt muscular adaptations. 

You can learn more about the M.A.X Muscle Plan in Brad Schoenfeld’s The M.A.X Muscle Plan 2.0.

References

1. Bloor, CM. Angiogenesis during exercise and training. Angiogenesis 8: 263-271, 2005.
2. Tsitkanou, S, Spengos, K, Stasinaki, AN, Zaras, N, Bogdanis, G, Papadimas, G, and Terzis, G. Effects of high-intensity interval cycling performed after resistance training on muscle strength and hypertrophy. Scand J Med Sci Sports 27: 1317-1327, 2017.
3. Mikkola, J, Rusko, H, Izquierdo, M, Gorostiaga, EM, and Hakkinen, K. Neuromuscular and cardiovascular adaptations during concurrent strength and endurance training in untrained men. Int J Sports Med 33: 702-710, 2012.
4. Schoenfeld, BJ, Ogborn, DI, and Krieger, JW. Effect of repetition duration during resistance training on muscle hypertrophy: A systematic review and meta-analysis. Sports Med 45: 577-585, 2015.

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