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Principle #1- Explaining Muscular Hypertrophy & Atrophy
The above diagram (Fig. 1) is an illustration of the basic training theory behind muscular hypertrophy and atrophy as a response to training stress. As you can see in Fig. 1, the initial response of the body after stimulus ins a decrease in performance. But after approximately 48-72 hours the body heals, recovers and actually begins to hypertrophy (grow). If another stress is placed on the body after in this period, you have a new starting point of increased performance and the body will continue to adapt positively to the training( as illustrated in Blue). If the next training period comes too soon and the body has not had enough time to recover. The new starting point is a point of less performance than the original. This is how over training occurs. The body is not allowed enough time to recover and is stressed before the body can heal (as illustrated by the redlines). If this pattern continues performance will continually decrease and the muscle will actually atrophy. An important point to note is that gains of hypertrophy and of performance usually only last for about one week per muscle group worked. If you are exercising each muscle group only once a week you may be only maintaining muscle, not promoting hypertrophy (Dr. Neil Little, KNSS 2110, lecture notes, 1997).
Factors Effecting the Curve: By Nevin Morrison
The value of using the curve as an illustration to explain muscular hypertrophy is that you can also illustrate the effects of different factors affecting the curve.
a) Amount of Stress: The amount of stress or the intensity level of the training can directly effect the curve and in effect cause the curve to have a bigger or smaller "Bounce." The higher the intensity of the workout the more muscular damage that will occur, in effect causing the healing phase of the workout to take longer and the hypertrophy phase to also be larger and longer (see Fig 1.1). The type of training can also effect the intensity. For example free weight exercises will damage more muscle fibers than machine exercises causing a higher stress level.
b) Muscle Size: The size of the muscle worked also changes the curve. Generally speaking the larger the muscle group stressed the longer the muscle takes to heal and grow. This causes a stretch in the curve (see Fig 1.2). The key training period for hypertrophy for large leg muscles may be well after 72 hours, while smaller muscle groups like the triceps may be ready to be trained again by the 48 hours.
c) Experience of the Weight Trainer: The law of diminishing returns is very applicable to this training curve. As the body adapts to weight training it becomes harder to stress the muscle as much even with a high intensity level. This in effect causes a flattening of the curve over time.(see Fig 1.3). This helps explain the need to periodically change your program in attempt to expose the body to new stressors.
d) Nutrition: Nutrition can have a major effect on the curve. Poor nutrition can lengthen the recovery phase of the curve and flatten the hypertrophy phase of the curve (see Fig 1.4).If your body does not have proper nutrition and a surplus of available calories the hypertrophy phase can become non-existent.
e) Rest: Lack of proper rest can have a similar affect to poor nutrition. Lack of rest can lengthen the healing phase and flatten the hypertrophy phase of the curve as illustrated in Fig 1.4.
f) Steroids: The use of anabolic steroids can directly effect the curve. The introduction of excess testosterone into the blood stream can shorten the healing phase and increase or maximize the hypertrophy phase (see Fig 1.5). Still the negative side effects caused by steroid use weight much heavier than any potential benefits in my opinion.
g) Creatine: The use of creatine can cause a larger bounce in the curve. Creatine if used properly can cause muscle fibers to fire repeatedly for a longer period than normal. This in effect will increase the stress put on the muscle causing more damage and increasing the bounce of the curve as seen earlier in Fig 1.1.
* There are many factors that can effect the training curve. Above are listed a few of these factors. This list will continue to grow as the field of kinesiology advances.