So as my interest in all things health and fitness continues, it would seem that everything becomes more and more scientific… which as a mega geek, I like as I get to investigate things in detail and write my findings for Fitness 101! I was recently discussing muscle hypertrophy with a friend, and I thought it would be good to write up my understanding thus far of the two types that you will hear people talking about; myofibrillar hypertrophy and sarcoplasmic hypertrophy.

Hypertrophy (pronounced “hi-per-tre-fee”)

So first of all what is hypertrophy? Muscle hypertrophy is the increase in size or growth of a muscle and it’s component cells normally from weight training or physical exercise. Initially you can start training and notice some strength increases without an increase in muscle size; this is because you are increasing the nerve impulses that cause the muscle to contract. If you continue to train the muscle, the cells will begin to grow larger and stronger in order to adapt to this stimulus.

Myofibrillar hypertrophy

Myofibrillar hypertrophy is the enlargement of the muscle fibre due to the increase in myofibrils in the muscle, which generate tension in the muscles which increases the trainees strength. It is generally associated with the type of training that a power lifter or athlete might do. The protocols for myofibrillar hypertrophy involve using heavy weights, typically in excess of 80% of the trainees 1RM (one rep max) in a low rep range (between 1-5 repetitions). Ideally the trainee will use explosive but controlled movements, with a quick tempo i.e 1 second concentric and eccentric movements, and they will have anything between 2-3 minutes rest between sets for the muscle to recover.

Sarcoplasmic hypertrophy

Sarcoplasmic hypertrophy is different, and is the enlargement of the muscle due to an increase in non-contractile muscle cell fluid, called sarcoplasm. It is generally associated with type of training that a bodybuilder will do. The protocols for sarcoplasmic hypertrophy involve using lighter weights, typically in excess of 60% of the trainees 1RM in a higher rep range (normally between 8-12 reps). The trainee will normally contract the muscle quite quickly in the concentric part of the movement i.e. in the pushing movement of the bench press, but will use a slower eccentric movement of 3-5 seconds to increase the time under tension. The rest period will be between 30 seconds – 2 minutes per set with a focus on getting the “pump” in the muscles.

So which type of hypertrophy is best?

Below is a diagram that shows a normal muscle fibre, an enlarged muscle fibre due to sarcoplasmic hypertrophy and an enlarged muscle fibre from myofibrillar hypertrophy.

sarcoplasmic hypertrophy vs myofibrillar hypertrophy

With sarcoplasmic hypertrophy, the muscle expands due to the increase of sarcoplasmic fluid but the density of myofibrils doesn’t change. Therefore the density per unit area decreases, and although the muscle increases in size there is little or no change in overall strength. With myofibrillar hypertrophy, the number of myofibrils increases creating an increase in strength. Most people will recommend training for myofibrillar hypertrophy because it provides functional benefits, however both are effective muscle builders and you won’t be able to tell the difference with the naked eye between the two types. Training for sarcoplasmic hypertrophy can produce quicker results for muscle size than myofibrillar hypertrophy. For a rounded muscle building routine, it would be advisable to include both types of hypertrophy in your training regime.

Conclusion

Although there are 2 distinct types of hypertrophy, it is actually very difficult to train just one or the other i.e. there is always some overlap.  Additionally, if overall size is your goal it is definitely worth including both types of hypertrophy in your training.  Below is an example of how this might be done for the bench press:

  • Warm up with 2 sets on a light weight
  • For the work sets, perform a set of 6-8 reps using a weight where you can do no more than 8 reps
  • Perform a set of 4-6 reps using a weight where you can do no more than 6 reps
  • Perform a set of 2-4 reps using a weight where you can do no more than 4 reps
  • Perform a set of 1-2 reps using a weight where you can do no more than 2 reps
  • Immediately after the last set, drop the weight back down to a weight where you can perform no more than 8-12 reps
  • As soon as you finish, perform push ups to failure

The work sets will provide the stimulus necessary for myofibrillar hypertrophy that will build strength, where the final sets in the higher rep range will exhaust the muscle and create the “pump”.

Alternatively you might choose to split your routine into days of heavy weight/low reps and a lighter weight/higher reps. Other options including training for strength for i.e. 6 weeks followed by 6 weeks of high volume in cycles.

As always if anyone has any thoughts, questions or differing opinions then please join the discussion and comment below.