Exercise for Muscle Growth

Hypertrophy is the term used to define muscle growth due to overuse. It happens when the muscles overcompensate in order to better cope with the stresses that are placed on them. The stresses are often in the form of resistance exercise (weight lifting) and they stimulate the 2 main types of hypertrophy, which are:

1. Myofibrillar Hypertrophy: An increase in the size of the contractile tissue. This type of hypertrophy is accompanied by an increase in the tensile strength and the force generating capability of the muscle.

2. Sarcoplasmic Hypertrophy: An increase in the volume of the sarcoplasm along with an increase in the amount of ATP molecules, glycogen, myoglobin, and other molecules related to energy conversion. It can also include an increase in the number of mitochondria. This type of hypertrophy is accompanied not by an increase in strength, but by an increase in the resistance to fatigue.

Although many training programs favor one over the other, each type of hypertrophy almost never occurs in complete isolation. A proper training program will stimulate both types of hypertrophy while accounting for the different muscle fiber types.


Stimulating Hypertrophy
Lifting heavy weights is best for stimulating myofibrillar hypertrophy because it places a great deal of tensile stress on the myofibrils (contractile tissue). You can do this by selecting weights that cause exhaustion after about 6 to 8 repetitions. Using much heavier weights than these will do more to stimulate neuromuscular strength than muscle growth. In addition, because ATP/CP is the primary fuel used during this type of training (see related article), using a reasonably long rest period such as 3 to 4 minutes is best for this type of training. On the other hand, training for sarcoplasmic hypertrophy is best done by using a moderately heavy weight that causes exhaustion at approximately 10 to 15 repetitions. The fatigue is caused by the exhaustion of ATP/CP, shortage of glycogen, and buildup of metabolic end products. When stimulating sarcoplasmic hypertrophy, a rest interval of about 1 to 2 minutes is often sufficient. Although either type of hypertrophy can be favored in a workout, neither type occurs at the complete exclusion of the other. It is also important to know that as the muscles adapt, the exercise must become more demanding in order to continue muscle growth. This is often referred to as progressive overload.

Training for Different Muscle Fiber Types
It is also important to know that different muscle fiber types respond differently to exercise. Fast twitch muscle fibers have a high force generating capability and they exhaust quickly. In addition, they respond very well to the types of training that are previously mentioned. Slow twitch muscle fibers do not fatigue as quickly as the fast twitch fibers. However, they have less force generating capability and they respond slowly. They are best trained by using very high repetitions (greater than 15) to complete exhaustion and with rest intervals of less than 1 minute. Because the various muscle groups have both types of fibers, a proper training program will stimulate both types based on their respective proportions within the muscle groups. For this reason, predominantly slow twitch muscle groups such as calves and abdominals demand higher repetitions. In addition, the genetics of the individual play an important role and must be considered.

Training for Optimum Results
There are many ways to stimulate both types of hypertrophy. One of the many ways is to adjust the training after every 4 to 6 weeks. Training for neuromuscular strength in some cycles and training for endurance in others can enhance this. This technique is one form of periodization, and is useful for enhancing both types of hypertrophy. In addition, there are many techniques that can be used to increase the intensity and/or volume of the exercises for optimum results. These techniques, often called supersets, include but are not limited to the following:

Rest Pause: This involves completing a set to exhaustion, resting for about 5 to 10 seconds for partial recovery, and then completing a shorter set to a second exhaustion.

Forced Reps: This involves completing a set to exhaustion, immediately followed by having a spotter assist you with additional repetitions.

Drop Sets (Stripping Sets) : This involves executing multiple sets in rapid succession while progressively reducing the weight between each set.

All of these are useful for providing acute stimulus for muscle growth. However, it is equally important that the stimulus is provided often enough so that the body can adapt without becoming deconditioned between each workout. This means training each muscle group at least once (preferably twice) per week. However, training too often can prevent proper recovery and quickly lead to over training. The best programs use a strategic mix of training days and rest days.