Pete McCall, author of Smarter Workouts, discusses metabolic conditioning and how to design your workouts efficiently.
Metabolic Conditioning = Muscle Growth:
Excerpted from Smarter Workouts by Pete McCall.
Exercise alone does not induce muscle growth. For muscle growth to occur, your body needs to experience at least one of three different conditions: metabolic or mechanical stress, more efficient glycogen storage, and stimulation of type II muscle fibers.
First, if you want to increase your lean muscle mass, the exercise you do must be challenging enough to create metabolic or mechanical fatigue in order to increase the amount of lean muscle. So, if your training doesn’t fatigue the muscles, you won’t help those muscles grow. Let’s explore how to apply the training stress in the right way to get the most out of your workout program.
When you exercise at the level where your body is using anaerobic glycolysis, you produce lactate and hydrogen ions (H++) as by-products of metabolic stress. The buildup of H++ is what makes you feel the burn, which is an indication that you are reaching a lactate threshold—i.e., that your blood contains more acidity and you’re not going to be able to generate as much energy until your body systems get rid of those by-products of high-intensity movement. This is your
sign that it’s time for a lower-intensity, active-recovery interval. HIIT, in the form of circuit training, can train your body on how to tolerate working at that threshold, as well as improve your body’s ability to quickly remove lactate and other metabolic waste. Metabolic stress induced by HIIT is an effective component of developing lean muscle; an exhaustive review of the research literature on training for muscle growth observed that high levels of metabolic stress can indeed lead to muscle growth (Schoenfeld 2010).
Mechanical stress, on the other hand, refers to the physical forces applied to muscle fibers. HIIT and resistance training damage the individual actin and myosin protein strands of muscle tissue, which, in turn, signal the biochemical reaction to produce new satellite cells responsible for repairing the mechanical structures via new proteins. This is one way in which exercise to the point of momentary muscle fatigue initiates muscle growth.
Like metabolic stress, mechanical stress is an important and essential stimulus for creating exercise-induced muscle growth. Similar to the age-old quandary of which came first, the chicken or the egg, we’re not sure which plays a greater role in muscle growth. Both occur simultaneously, making it difficult for researchers to identify which has more influence on muscle growth. However, we do know that exercising to the point of momentary fatigue combined with short rest intervals can create both the mechanical and metabolic stimulus that could lead to muscle growth.
Determining the right type and amount of metabolic or mechanical stimulus for your needs will take some trial and error. While both result in muscle growth, the fact is that metabolic and mechanical stress can also cause muscle soreness. A moderate-to high-intensity workout should leave you slightly fatigued by the end; you don’t want to be completely wasted, but you definitely want to feel like it would be tough to continue exercising at the same level of intensity. The day after a properly challenging workout should leave you feeling like you exercised the day before; you don’t want to feel any extreme soreness or pain—that is an indication that you did too much work or damaged some tissue—but you definitely want to feel the muscles that you used during the workout. If you do feel any pain, it will be important to rest for a couple of days, and if it continues, it may be necessary to check with a medical professional to make sure that nothing is injured.
Besides stimulating the production of the hormones responsible for muscle repair, a second way that high-intensity, physically challenging exercise creates muscle growth is due to the amount of muscle glycogen used for ATP production. Exercise to the point of fatigue will deplete the amount of glycogen in muscle cells. As a result, the muscle cells will become more efficient at storing glycogen for future use. Glycogen storage provides necessary energy, which can help you sustain longer bouts of exercise: You improve your endurance. It’s important to note that when it’s stored in muscle tissue, one gram of glycogen holds approximately three to four grams of water. As your muscle cells adapt to store more glycogen, they will also store more water, leading to an increase in size (Schoenfeld 2013).
The third way that metabolic conditioning produces muscle growth is by stimulating the type II motor units and muscle fibers responsible for fast, high-velocity movements. Dynamic, power-based movements use primarily type II muscle fibers because of the requirement for immediate energy from anaerobic sources. Exercises such as jumps, medicine ball throws, and kettlebell lifts like the swing, clean, or push press maximize the power output of your muscles. The end result of a metabolic conditioning workout featuring power exercises is that you get results you can see. For example, consider sprinters who train to be as fast as possible when running 100- or 200-meter races. Sprinting requires fast, power-based muscle actions, leading to activating more type II fibers, ultimately resulting in sprinters having lean, muscular physiques.
To optimize your aerobic efficiency during exercise, you should try to work at an intensity where your breathing is quick but under control, and you can talk without too much difficulty. On a scale of 1 to 10, where 10 is the hardest, this would be about 5 or 6. Staying at this intensity means that you will optimize your aerobic efficiency instead of simply trying to work as hard as possible.