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Reps For Muscle Hypertrophy

There has been much discussion and debate on the best training methods for muscle hypertrophy, with many views based on personal experience. I thought it would be interesting at looking at the different aspects involved in inducing muscle hypertrophy, and if there are any training methods we can use to cause optimal results in this regard.

Before we start looking at the various aspects involved in inducing muscle hypertrophy it would be best if we first declare what muscle hypertrophy actually is. In simple terms, muscle hypertrophy is the growth and increase in size of muscle tissue. We must note that this is the increase in size of existing muscle fibres, and not the creation of new muscle cells, which is a different process called muscle hyperplasia. Muscle hypertrophy can be categorised into two types; sarcoplasmic hypertrophy - the increase of sarcomplasmic fluid resulting in the increase in muscle size with less gains in strength, and myofibrillar hypertrophy - the increase in size of muscle myofibrils, resulting in some muscle size increase, and also strength gains.

As we can see, muscle hypertrophy is usually the aim of the bodybuilder, and those looking to increase muscular size. Now lets look at the various aspects of inducing muscle hypertrophy:

Anabolic hormones and lactic acids role in muscle hypertrophy

I am sure you have felt lactic acid build up before, a process often interpreted by many lifters as a barrier to completing a set to its full potential, a negative and useless bi-product of exercise. During the early stages of carbohydrate catabolism to fuel the energy needs of muscle contraction during moderate repetition weight training, the bi-product lactic acid is produced which can in turn lead to the excretion of powerful anabolic hormones¹. Lactate has been shown to lead to a higher level of both Testosterone and growth hormone, a process that can also lead to the heightened levels of the very powerful hormone IFG-1.

Although this process has been shown to decrease with age somewhat², it is a strong argument for the use of moderate repetition weight training for inducing muscle hypertrophy, compared to lower repetition work. Lower repetition training has a more reduced surge of anabolic hormones due to the shift in energy source (phosphocreatine), resulting in less lactic acid build up.

Fast twitch fibres and muscle fibre recruitment in muscle hypertrophy

It is commonly accepted that fast twitch fibres (particularly the red type IIA) possess more potential for growth, and therefore performing exercises that recruit these muscle fibres primarily will result in muscle hypertrophy to a greater degree. The faster twitch fibres contract quicker, have greater mitochondrial and capillary density, and have lower resistance to fatigue. Low to moderate repetition work with a challenging resistance will recruit these fibre types to the greatest degree.

The difference usually between low repetition training and moderate repetition weight training is that the moderate repetition training has a greater time under tension (TUT) which prolongs the cross bridge formation, this usually leads to greater muscle fibre damage to maximise the potential for muscle hypertrophy.

The pump and its role in muscle hypertrophy

The pump, a term used to describe the increase in blood flow (and fluid build-up) to an exercised area causing the muscle to become full and tight. The pump is often believed to be a short lived egotistic aspect to training, resulting a short period of time where a trained muscle feels and looks great, purely aesthetical. When we start to truly understand the process that is happening within the muscle during this time, we may come to appreciate the pump a little more, and start to understand why the greats such as Arnold Schwarzenegger used to speak of the phenomenon so highly.

The pump feeling is caused due to myofibril hydration, a process that can greatly aid in protein synthesis to occur, creating the ideal conditions for muscle growth. With arteries pumping blood into the working muscles, and the veins that take the blood out of the muscles collapsing, the result is blood plasma build up in the spaces between the muscle cells and blood vessels. This can surge to a level where the plasma seeps back into the muscle, resulting in the pump. This process happens with moderate repetition training, and is a process that many trainers will have felt. This process if much less pronounced in low repetition resistance training.

Summary

Above are a few aspect to muscle hypertrophy which go beyond the normal mechanical stress to muscle fibres which is often the only aspect many trainers think and talk about when it comes to muscle hypertrophy. Of course, there will still be many that disagree with the concept that moderate repetition training is optimal for muscle hypertrophy, with many stating that training programs such as the 5 x 5 is much better then high repetition work for "gains" (I used that term because many people mistake strength gains as muscle size gains). We must consider that every body that trains will react differently to different stimuli, so it would be impossible to give a universal answer to the question of the ideal rep range for muscle growth. What we can do however is look at studies, look at the aspects that are involved in the process of muscle hypertrophy, look at personal experiences, and try to draw a conclusion on what sort of rep range will likely be optimal for the majority of bodybuilders. From looking at such aspects I believe that moderate repetition work, the programs that many bodybuilder have used in the past, and continue to use to this day, is optimal for muscle hypertrophy. Not everybody agrees and have counter-arguments for that claim, that’s what makes this topic much debated and much interesting!

1. Hormonal and growth factor responses to heavy resistance exercise protocols. Exercise Physiology Division, US Army Research Institute of Environmental, Natick, Massachusetts 01760-5007.
2. Acute hormone responses to heavy resistance lower and upper extremity exercise in young versus old men. Department of Biology of Physical Activity, University of Jyväskylä, Finland.

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