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Wing Fibers
Muscle Hypertrophy and Fiber Types
Muscle Hypertrophy & Fiber Types.
What is hypertrophy?
As it relates to strength and muscle, hypertrophy is simply the enlargement of a muscle belly due to an increase in the size of muscle cells - particularly the muscle's fibers.
Human skeletal muscle undergoes hypertrophy (i.e. it gets bigger) following a resistance training program. But is this whole-muscle hypertrophy the result of fiber hypertrophy or fiber hyperplasia. In other words, do muscles get bigger due to an increase in existing fiber size or an increase in the number of fibers?
It's a subject that had stirred much debate amongst researchers. While fiber hypertrophy is well accepted and documented, very few studies have measured fiber hyperplasia in humans. Studies on animals have shown conflicting results.
Studies on cats have found that hyperplasia occurs in response to heavy resistance training - cats were trained to move a heavy weight with their paw in order to get food. In contrast, other studies on chickens, rats and mice have found that overload resulted in muscle hypertrophy only and no change in the number of muscle fibers. The differences in results between the cat and other animal studies may be a result of the overload used. The cats were exposed to high resistances and low repetitions as opposed to more endurance-type activity used in the other studies.
A further study performed on birds reported an increase in the number of muscle fibers in the wing in response to chronic stretching by attaching a weight to it. Follow up studies using a similar model have both confirmed and contradicted these results.
Chronic hypertrophy & transient hypertrophy.
The long-term increase in muscle size is referred to as chronic hypertrophy. Short-term or transient hypertrophy refers to the pump in -up of muscle that occurs during a resistance training session. This is predominantly due to fluid retention in the interstitial and intracellular spaces of the muscle and is known as edema.
Muscle Anatomy?
Each muscle or muscle group (like the biceps) is made up of bundles of muscle fibers. Traditionally, researchers believed that the number of fibers we are born with doesn't change, regardless of any exposure to resistance training. This is contested by many proponents of muscle fiber hyperplasia, who suggest that training may induce a greater number of fibers to be formed.
According to the principle of hypertrophy, muscles become larger following a strength training routine, in part, because each fiber (usually fast twitch) becomes larger or thicker. One or more of the following adaptations cause the increase in fiber size.
- Increase in the number of contractile proteins (actin and myosin)
- Increase in the number and size of myofibrils per muscle fiber
- Increase in the amount of connective tissue
- Increased enzymes and stored nutrients
How muscle size increase?
The increase in individual fiber size seems to be stimulated by an increase in muscle protein synthesis. During intense exercise, protein synthesis appears to decrease and then increase during the recovery period.
- The opposite is true for the breakdown or degradation of protein. This increases during and immediately following exercise and decreases in the recovery period.
- Taking a carbohydrate and protein supplement immediately after a resistance training sessions has been shown to reduce the rate of protein degradation.
- Interestingly, eccentric muscle action appears to induce a greater amount of muscular hypertrophy compared to concentric muscle action. Comparing training regimens of only concentric or eccentric exercises, one study found hypertrophy in fast twitch fibers was ten times greater in the eccentrically trained group.
Muscle fiber types?
Muscle fibers are designed either for aerobic metabolism or for anaerobic activity. Two muscle fiber types have been identified and classified as slow twitch (Type I) and fast twitch (Type II). Slow twitch (Type I) are more suited for long, low to medium intensity activity and fast twitch (Type II) is more suitable for short duration, high intensity activity. A Weightlifter need high percentage of type II fibers to perform explosively.
Type I and Type II was the standard classification for muscle fiber types. Fast twitch was also further divided into Type IIa and Type IIb fibers. Type IIa was called fast oxidative glycolytic because of its ability to perform both aerobic and anaerobic metabolism. Type IIb was coined fast glycolytic because it has the greatest anaerobic capability. Eventually more subtypes of each fiber were identified. Type I fibers were broken down into Type I and Type Ic. Type Ic is believed to have less oxidative ability than Type I. Type II fibers were broken down even more into Type IIc, IIac, IIa, IIab, and IIb. Each has different aerobic and anaerobic characteristics. In a study done where they randomly selected youth athletes and determined the percentage of type I fibers in their Vastus Lateralis. The long distance runners came out on top with roughly 60%-95% Type I fibers while the sprinters had roughly 15%-38% Type I fibers.
It is largely believed that genetic factors influence the percentage of each muscle fiber type in a person. However, in elite athletes depending on which sport they participate in they will have a fiber type that is more favorable for that sport. That simply means endurance athletes had more Type I and a weightlifter or sprinter had more Type II muscle fibers. However, there are conflicting views on exercise changing muscle fiber type. Some studies have shown a change in Type I fibers after endurance training while others have not. Although it seems that high intensity resistance training causes a transformation of Type IIb into Type IIa. Similarly a high intensity and endurance training program increased their Type IIa and Type IIc, IIc is the most oxidative of the Fast twitch.
Subtype transformations seem to occur within two weeks. However, with lack of training the subtype will go to their original state.
It is easy to understand that how we can recruit fast twitch fibers with properly designing a resistance training program. This program can help in hypertrophy and muscle recruitment. Fast twitch fibers are the muscles that are linked with the speed and explosive qualities. The sports like Olympic weightlifting need more and fast twitch fibers to improve the performance.
By:-
Khizer Hayat Raja
Sr. Lecturer in Physical Education & Sports
International Weightlifting Coach & Expert
E. mail: wlexpert@yahoo.com
About the Author
Affiliated with Olympic style weightlifting since 1989. First as player and from 1998 as a coach. Author of a book and keen in research work.
Presently serving as Sr. Lecturer in Physical Education and Sports at a College. Coaching and training many Juniors & Seniors in Olympic style weightlifting. Produced many National and International weightlifters within and out side the country.
Senor Liftow