Anatomy of a Muscle
Human skeletal muscles, often known as voluntary muscles, are composed of bundles of fibers called Myofibrils. The fibers are surrounded by a gelatinous, semi-transparent fluid called sarcoplasm. Sarcoplasm is essentially a storage depot for glycogen, a form of sugar used for short term energy. The individual fibrils are made up of sarcomeres which, when they contract, are responsible for the actual movement. A single muscle cell may contain as many as 100,000 sarcomeres. Here’s a diagram courtesy of (Fig. 12.2 from Fox, S.I. Human Physiology, 4th Ed.Wm.C. Brown, publ.):
When you perform hypertrophy training, there are two main adaptations that can happen:
1) Growth of sarcoplasm, this allows for greater temporary energy storage and is most stimulated in the higher rep ranges, say 9-13 reps or so. It will occur with any hypertrophy training to a greater or lesser degree depending on the type of training. Bodybuilders usually elicit a large portion of their growth from this form of adaptation, which is why they sometimes look “softer” than say a gymnast or Olympic lifter.
2) Growth of sarcomeres, this creates an increase in contractile strength and is most stimulated in the middle rep ranges, say 5-8 or so. Again, it will occur in any hypertrophy training to a greater or lesser degree depending on the type of training. This sort of muscle tends to look harder and more compact.
Since our goal is muscle retention during fat loss, we’re going to want to focus on those two type of muscular adaptations, as they’re the ones that most prevent breakdown of tissue during a calorie deficit.
Exercises are usually expressed in terms of sets and reps. Lets use the squat as an example, which you can see here:
http://www.exrx.net/WeightExercises/GluteusMaximus/BBSquat.html
Going up and down one time would be a repetition. A group of repetitions would be a set. So if you did eight reps, that would be a set. If you paused, then did eight more reps that would be two sets. In notation the sets always come first, then the reps, then the weight, like this:
4 x 8 x 225
That would be four sets of eight reps of 225lbs.
5 x 5 x 212
That would be five sets of five reps of 212lbs. (Which happens to be what I did on Tuesday, not a huge number but decent for about four months worth of training after being out of the gym for so long).
The combination of sets, reps, and weight determines what the training adaptation will be. If you multiply sets times reps, the hypertrophy range is normally considered to be from 25-54 or thereabouts. So 5×5, 4×8, or 3×10 will all produce hypertrophy adaptations, with the exact ratio of sarcoplasm/sarcomere growth varying somewhat with the number or reps. (and the trainees strength curve, fiber type distribution, training age, etc.)