In a series focused on muscle growth and fat loss, we'd be remiss to gloss over the concept of muscle growth itself, or in more formal terminology, muscular hypertrophy. Muscular hypertrophy is simply the increase in size of skeletal muscle. In other words, muscular hypertrophy is the process of making your muscles grow larger! 1
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So how do you facilitate muscular growth?
Mechanical tension, muscle damage, and metabolic stress all can play a role in exercise-induced muscle growth.
There are three primary factors that are theorized to induce muscular hypertrophy. 2-4 They are:
- Mechanical tension
- Metabolic stress
- Muscle damage
What is mechanical tension?
Mechanical tension is the type of force that is used to try to stretch a material.Chris Beardsley
In layman's terms, mechanical tension in resistance training is the force that is used to move weight in an exercise. For example, you create mechanical tension during a bench press in order to push the weight off of your chest.
There are various ways to increase mechanical tension, but the most popular methods are increasing the weight lifted (intensity) and increasing the time under tension.
By increasing the amount of weight lifted, or intensity, you are forcing your muscles to create more force to lift the weight, leading to increased mechanical tension. You can increase the time under tension by going through your reps more slowly. By slowing down your reps, you are creating more muscle tension over a longer period of time, increasing the workload of your muscles, and adding to mechanical tension.
What is metabolic stress?
Metabolic stress is a physiological process that occurs during exercise in response to low energy that leads to metabolite accumulation in muscle cells.World Journal of Methodology
In laymen's terms, metabolic stress training is training that maximizes blood flow in the muscle. This increased blood flow drives metabolites into the muscle, such as lactate and hydrogen, that facilitate muscle growth. In gym culture this increase in blood flow is called "the pump", a term popularized by Arnold Schwarzenegger.
Chris Beardsley's article on metabolic stress describes how to achieve metabolic stress from a bodybuilder's perspective (someone whose sole focus is to build muscle size). Bodybuilders will lift weights in a controlled manner and aim to lift a moderate amount of weight for a higher number of repetitions. This causes greater metabolic stress than faster reps at a lower rep range.
What is muscle damage?
Muscle damage occurs when the internal structures of a muscle fiber, or its outer wrapping layers, are damaged.Chris Beardsley
While it may sound harmful, muscle damage is not necessarily a bad thing when it comes to muscle growth! During resistance training, you create small tears in the muscles you exercise. With proper rest and nutrition post-workout, your body then repairs these micro-tears and builds the muscle back, oftentimes bigger and stronger. In this sense, muscle damage is crucial to muscle growth!
Resistance training resulted in hypertrophy of the total muscle cross-sectional area (CSA).
Mechanical tension, metabolic stress, and muscle damage are the three primary factors that are theorized to induce muscular hypertrophy.
Though this may sound complicated, a simple way to introduce all three of these factors is resistance training (most commonly in the form of lifting weights). 2-4 Of course, this leads to various other questions such as "What kind of resistance training is best for optimal muscle growth?"
Fear not! There are many factors that contribute to muscle growth in a training program, and we'll be covering all of them in this series. Stay tuned!
- Baechle, Thomas R.; Earle, Roger W., eds. (2008). Essentials of strength training and conditioning (3rd ed.). Champaign, IL: Human Kinetics. ISBN 978-0-7360-5803-2. Link
- Schoenfeld BJ. The mechanisms of muscle hypertrophy and their application to resistance training. J. Strength Cond. Res. Oct 2010;24(10):2857–2872. Link
- Mccall GE, Byrnes WC, Dickinson A, Pattany PM, Fleck SJ. Muscle fiber hypertrophy, hyperplasia, and capillary density in college men after resistance training. J Appl Physiol. 1996;81(5):2004-12. Link
- Staron RS, Karapondo DL, Kraemer WJ, et al. Skeletal muscle adaptations during early phase of heavy-resistance training in men and women. J Appl Physiol. 1994;76(3):1247-55. Link