Within the context of our individual athletic endeavors, we have our goals we would like to reach or attributes we would like to enhance. For example, some of us would like to complete a marathon or tough mudder, or maybe you want to deadlift 500lbs or have a 30 inch vertical or run 400 meters in under 60 seconds (this one is especially unfun…..if that’s a word). For each one of these goals, their comes a certain training style that will get you there quicker, which can be found in some form or another in the repetition continuum (the RC from now on). True understanding of the RC starts with a basic understanding of physiology and what certain exercise does to the body. That is where we will start today.
Before we get started, their are 3 basic things you need to keep in mind about the RC as we move forward:
1) Strength & Endurance CANNOT be optimally developed at the same time since they are at opposite ends of the continuum
2) Developing maximal strength increases the potential for maximal endurance
3) Strength takes longer to develop than endurance
Our bodies are composed of 3 distinct muscle fiber types: type I, type IIa and type IIb. Type I is red in color because of the number of mitochondria and is known as the slow-twitch muscle fiber. Type I fibers have primarily used for endurance purposes and have the least potential for hypertrophy (more on this later). Type IIa are pink in color and are adaptable fibers, meaning depending on how you train, they will adapt to be more endurance based or more strength/power based. Finally, type IIb fibers are known as fast twitch muscle fibers, which are white in color. Fast twitch fibers fatigue quickly because they only use anaerobic metabolism, but they contract rapidly and have the most potential for hypertrophy. These are primarily used for strength/power movements.
Muscle fibers are controlled by motor neurons, which collectively are known as motor units. How many muscle fibers that correspond to a single motor neuron depends on how much control the motor unit needs. For instance, a motor unit that controls your eye may only have a small bunch have muscle fibers related to it, because your eye requires very precise movements. On the other hand, a motor unit for a quadriceps muscle may have thousands of fibers because your quads are used for more gross movements. Motor units are categorized similar to muscle fibers. Low threshold motor units (LTMUs) generally correspond to type I fibers, so are more endurance based, while high threshold motor units (HTMUs) correspond to type IIb fibers and are more strength/power based.
As noted before, type IIb fibers have a greater propensity for hypertrophy than type I fibers, which also means that HTMUs are better utilized for hypertrophy than LTMUs. But hypertrophy can happen at a couple of different levels.
So what is hypertrophy anyway? Hypertrophy is defined as the enlargement of an organ or tissue due to increase in size of its constituent cells……in our case muscles and their cells. Myofibrillar and sarcoplasmic hypertrophy are 2 types of hypertrophy that occur primarily in HTMUs and LTMUs respectively. With HTMUs, actin and myosin proteins, or proteins which help your muscles contract, are broken down. In response, your body start adding more of these contractile proteins – AKA myofibrils – to help with muscular contraction (getting stronger), creating myofibrillar hypertrophy. On the other hand, LTMUs add additional proteins and metabolites which draw more water into the cell (getting bigger) creating sarcoplasmic hypertrophy. Have you ever heard the saying “look like Tarzan, play like Jane”? This is where that saying can be explained, and is also why you can put a 200lb bodybuilder next to a 200lb powerlifter and the powerlifter will out lift the bodybuilder by atleast 25%.
This basic physiology understanding will help us as we dive into the repetition continuum. Next we’ll take a look at the basics of the RC itself and how we can start to apply it to our own training.