What is hypertrophy during exercise?
According to the definition, hypertrophy is the enlargement of an organ or tissue through the increase of its cell size. This must not be confused with hyperplasia. Hyperplasia is the enlargement of an organ or tissue through the increase in the reproduction rate of its cells, thus increasing in cell number.
The regularity with which a muscle is used as well as the intensity and duration of its activity affects the properties of the muscle involved. The increased amount of contractile activity exercise, in other words, can produce an increase in the size of muscle fibers as well as changes in their capacity for ATP (bodies form of energy) production.
Hypertrophy is what happens when you do strength/resistance training where you see an increase in muscle size. Strength training is an anaerobic exercise, this means oxygen is not needed to produce energy for the muscle cells because it takes too long from breathing it in and being transported to the active muscle cells to produce energy. Instead, the muscles use already stored energy which is much faster to utilize. Hypertrophy is when your body adapts to a regular increased workload causing stress to your muscles and the only way the muscles can cope with it is by getting stronger.
The number of muscle fibers remains essentially constant throughout adult life, the changes in muscle size with hypertrophy do not result from changes in the number of muscle fibers but in the metabolic capacity and size of each fiber.
Short duration, high-intensity training or strength training such as weight-lifting and sprinting affects primarily the fast-glycolytic fibers which are activated during strong muscle contractions. These fibers undergo an increase in fiber diameter due to the increased synthesis of actin and myosin filaments which form more myofibrils.
In addition, glycolytic activity is increased by increasing the synthesis of glycolytic enzymes. The result of such high-intensity exercise is an increase in the strength of the muscle and the resulting bulging muscles of a weightlifter. Such muscles, although very powerful, have little capacity for endurance and fatigue much faster.
