Hypertrophy and Muscle Growth

A detailed look at myofibril and sarcoplasmic hypertrophy, and how to train using both to maximize muscle mass gains.

“Hypertrophy.” When that word is said everybody who works out has an opinion. General conversations go something like this:

Hypertrophy Noob Lifter

So what is the best way to achieve hypertrophy? The reality is that there is not a single kind of hypertrophy, and you must do different types of training to target the two broad types of hypertrophy. What are the two types? Hypertrophy can be broken down into two broad types:

Myofibril hypertrophy.

Myofibrils are essentially bundles of myofilaments (The contractile parts of a muscle, the parts that pull). They are found in each skeletal muscle fiber.

Each muscle cell contains many myofibrils. Myofibril hypertrophy occurs due to an overload stimulus (lifting more than your body is used to) that applies trauma to the individual muscle fibers. Your body treats this as an injury and as such overcompensates during the recovery process by increasing the volume and density of the myofibrils so that the “injury” does not occur again.

This is one of the reasons why you must maintain overload to continue making gains.

Sarcoplasmic hypertrophy.

The sarcoplasm is the fluid and energy sources that surround the myofibrils in the muscle. It includes things such as ATP, glycogen, creatine phosphate and water. Increase in size of blood vessels that provide blood to the muscles can also be included in sarcoplasmic hypertrophy and is commonly referred to as capillirisation.

This occurs much in the same way as myofibril hypertrophy, through your body overcompensating during the recovery phase after your energy sources have been depleted during a workout. It therefore increases energy stores such as ATP and glycogen to prevent depletion during training.Muscle Hypertrophy

Ok, so I know the two types. What are the best ways to achieve both?  Before I go on I want to stress that you:

Choose the weight for your reps NOT the reps for your weight.

Progressive resistance exercise or progressive overload refers to the practice of continually increasing the stress placed on the muscle as it becomes capable of producing greater force or has more endurance. (Fleck S. J. and Kraemer W.J.,1997). This means that you MUST use weights and rep ranges that you struggle with.

You should choose a weight that you can only just complete the desired reps for. Do not choose a weight and get nearly the reps that are required, or one that is too light that you could complete many more reps. So for a 12 rep exercise, choose a weight that you can only just complete those 12 reps.

Myofibril hypertrophy training:

Strength training with 80%+ of your 1RM and reps in the 3-8 range with 2-4 minutes rest produce the largest changes in myofibrillar volume and density. Therefore if you want to achieve myofibril hypertrophy you must lift heavy. The heavier the weights you lift the more muscle fibers are recruited and in turn damaged. However it is recommended to keep the reps between 3-5 as any lower and it is mainly neuro-muscular adaptations that improve the athletes strength rather than through myofibril hypertrophy (Zatsiorsky, 1995).

“In fact low reps are essential for achieving maximal growth” - Charles Poliquin 1997.

Sarcoplasmic hypertrophy training:

Sarcoplasmic hypertrophy is achieved through what is known as fatigue training. Fatigue training is training at an intensity ~75% of your 1RM with reps in the range of 10-15 and short rest periods 45-90 seconds. It is referred to as fatigue training as it rapidly and directly uses up a lot of the stored energy in your muscle cells and fatigues your muscles.

When choosing the amount of sets for your workouts you must take into account the time under tension. There is a minimum amount of time under tension required for muscle hypertrophy to occur. Due to this it is generally required to complete more total sets for your strength training routine than your higher rep fatigue training routine.

In fatigue training you want to time under tension to be greater than the immediate energy available. The most immediate energy sources for short term anaerobic exercise is your ATP and creatine phosphate stores. These however are very short term and as such will be depleted in 7-10 seconds. After this your body will break down glycogen for energy, which will produce lactic acid (the burn). Therefore you must maintain a time under tension of over 10 seconds per set in fatigue training. The inclusion of slower reps, or methods such as same muscle supersets are a great way to achieve this.

Why cant I train both in a single rep range?

There is a spectrum through which myofibril and sarcoplasmic hypertrophy occur:

  • 1-5 Reps - Lead to a maximum increase in relative strength and myofibril recruitment.
  • 6-8 Reps - Produce the best medium between myofibril and sarcoplasmic hypertrophy.
  • 9-12 Reps - Increase sarcoplasmic hypertrophy at the maximum rate.
  • >15 Reps - You move into the range of muscular endurance where hypertrophy gains slow.

Myofibril damage will not just cease to happen at >12 reps, but it will be to a lesser degree and with less muscle fiber recruited than at lower reps.

Put it this way, why would you want to train at a rep range in which you are not getting maximum gains in either sarcoplasmic or myofibril hypertrophy? When you can train both maximally without deceasing gains in the other. I will explain how this can be achieved further down.

Ok so myofibril hypertrophy is best achieved through strength training and sarcoplasmic hypertrophy through fatigue training. What is the best way to achieve both?

Bodybuilder performing lat pulldowns for hypertrophy.

I’m sure you are aware of the dominance of the Eastern Bloc countries during the 50’s, 60’s, 70’s and 80’s. This can attributed to many things, notably the use of periodization.

Periodization in the West was very basic and often unused in many cases until the release of information from the Eastern bloc coaches. Periodization is the method of training specific goals in a cycle. Periodization can be broken down into 3 main categories:

  • Microcycle: Is very short term, usually around a week.
  • Mesocycle: Longer term cycles usually several weeks.
  • Macrocycle: Long term cycles for several months, even years.

Now conventionally people use mesocycles for their training, they do a set program for 8-12 weeks, say a strength program. They then swap and do for example a cutting program for another 8-12 weeks. While this type of training can produce results in a single area, it is very linear and as such you will regress in certain areas. It is also difficult to maintain overload on a program done for many weeks/months.

This is where the Eastern Bloc training comes in. Many Eastern Bloc coaches used very short term microcycles for their training, they would train towards many different goals in a few weeks. For example:

  • Week 1: Relative strength training.
  • Week 2: Power and speed development.

These can be repeated for many months with only slight changes and overload can be achieved more easily as the body finds it more difficult to adapt to rapid changes in training style.

So to achieve maximal hypertrophy I recommend you use 2-3 week long microcycles e.g.

  • Week 1: Strength training, 4 day split.
  • Week 2: Fatigue training, 5 day split.
  • Week 3: Recovery, 2 day full body split.

It is also possible to use even shorter intra-workout cycles for example starting a routine with an upper body strength exercise with reps in the range of 2-6 for 5-6 sets then moving on to higher rep (8-15), lower rest training for another 3-4 exercises.

A good example of a routine like this is Westside for Skinny Bastards which trains both low rep max effort training alongside higher rep fatigue training. It is important to note that if you do decide to undertake or create such a program that you make sure you perform the heavier max effort lifts first. This is due to the advantage in exciting your nervous system before continuing for more exercises. To put it another way your nervous system is warmed up and working to maximum efficiency after completing some heavy sets.

A study comparing the effects of linear vs. periodization changes in college athletes showed that the linear trained athlete’s strength increased 14.15% over 12 weeks compared to 23.53% for the athletes using periodized training programs. (Prestes J, Frollini AB, 2009)

So there we have it, a different approach to achieving muscle hypertrophy. If you like the sound of this my recommendation is to try it. I have tried many different routines in the past and without a doubt short term strength/higher rep cycles have worked best for me. Many other professionals also use this type of training including pro natural bodybuilder Joe Ohrablo who frequents these forums.

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  • Prestes J, Frollini AB, de Lima C, Donatto FF, Foschini D, de Cássia Marqueti R, Figueira A Jr, Fleck SJ. Physiological Sciences Department, Exercise Physiology Laboratory, Federal University of São Carlos, 2009