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http://www.coachr.org/fiber.htm
Dit is een interressant artikel dat ik jullie niet wilde onthouden
, een paar stukjes uit het artikeltje:
RECRUITMENT OF MUSCLE FIBERS
Muscles produce force by recruiting motor units (a group of muscle fibers innervated by a motor neuron) along a gradient. During voluntary isometric and concentric contractions, the orderly pattern of recruitment is controlled by the size of the motor unit, a condition known as the size principle (Henneman, et al., 1974). Small motor units, which contain slow-twitch muscle fibers, have the lowest firing threshold and are recruited first. Demands for larger forces are met by the recruitment of increasingly larger motor units. The largest motor units that contain the fast-twitch B fibers have the highest threshold and are recruited last.
No matter what the workout intensity, slow-twitch motor units are recruited first. If the workout intensity is low, these motor units may be the only ones that are recruited. If the workout intensity is high, such as when lifting heavy weights or per- forming intervals on the track, slow- twitch motor units are recruited first, followed by fast-twitch A and fast- twitch B, if needed.
There is some evidence to suggest that the size principle could be altered or even reversed during certain types of movements-specifically those that contain an eccentric (muscle lengthening) component-such that fast-twitch motor units are recruited before slow- twitch motor units (Denier van der Gon, et al., 1985; Grimby & Hannerz, 1977; Nardone, et al., 1989; Smith, et al., 1980; Ter Haar Romeny, et al., 1982). It is possible that a preferential recruitment of fast-twitch motor units, if it exists, is influenced by the speed of the eccentric contraction, and can only occur using moderate to fast speeds (Karp, 1997; Nardone, et al., 1989).
IMPLICATIONS FOR TRAINING
Training a FT -fibered muscle for endurance will not increase the number of ST fibers, nor will training a ST-fibered muscle for strength and power increase the number of FT fibers. With the proper training, FT -B fibers can take on some of the endurance characteristics of FT -A fibers and FT -A fibers can take on some of the strength and power qualities of FT-B fibers. However, there is no inter-conversion of fibers. FT fibers cannot become ST fibers, or vice versa. What an athlete is born with is what he or she must live with.
Although the type of fiber cannot be changed from one to another , training can change the amount of area taken up by the fiber type in the muscle. In other words, there can be a selective hypertrophy of fibers based on the type of training.
For example, an athlete may have a 50/50 mix of FT/ST fibers in a muscle, but since FT fibers normally have a larger cross-sectional area than ST fibers, 65% of that muscle's area may be FT and 35% may be ST. Following a strength training program for improvement in muscular strength, the number of FT and ST fibers will remain the same (still 50/50), however the cross-sectional area will change. This happens because the ST fibers will atrophy (get smaller) while the FT fibers will hypertrophy (get larger).
Depending on the specific intensity used in training, the muscle may change to a 75% FT area and a 25% ST area. The change in area will lead to greater strength but decreased en- durance capabilities. In addition, since the mass of FT fibers are greater than that of ST fibers, the athlete will gain mass, as measured by the circumference of the muscle.
Conversely, if the athlete trains for muscular endurance, the FT fibers will atrophy while the ST fibers hypertrophy, causing a greater area of ST fibers. The area of the muscle, which began at 65% FT and 35% ST before training, may change to 50% FT and 50% ST following training, The endurance capabilities of the muscle will increase while its strength will decrease, and the athlete will lose some muscle mass, again be- cause ST fibers are lower in mass than FT fibers. The decrease in mass may be observed by a smaller circumference of the muscle.
Many coaches know that, for gains in muscular strength, one should train with heavy weights and few repetitions. This training regimen works because using heavy weights recruits the FT -B fibers, which are capable of producing a greater force than the ST or FT -A fibers. Hypertrophy will only occur in those muscle fibers that are overloaded, so the FT - B fibers must be recruited during training in order to be hypertrophied (Morehouse & Miller, 1976).
Training with a low or moderate intensity will not necessitate the recruitment of the FT -B muscle fibers. Therefore, the training intensity must, be high. But how heavy a weight and how many repetitions should you use?
Muscular strength is primarily developed when an 8-repetition maximum (8RM, the maximum amount of weight that can be lifted eight times ) or less is used in a set. When the aim of training is to increase the neuro- muscular component of maximum strength, at least 95% of the athlete's 1RM and 1 to 3 repetitions should be used. When the aim is to increase maximum strength by stimulating muscle hypertrophy, at least 80% of 1RM should be lifted 5 to 8 times or until failure (Zatsiorsky, 1995).
This latter recommendation assumes that the focus of training is hypertrophy for strength, rather than hypertrophy simply for muscle size. If the aim of training is to increase muscle size (hypertrophy) with moderate gains in strength, then 6 to 12 repetitions should be used (Fleck & Kraemer, 1996). Remember, in order to improve muscular strength, FT -B fibers must be recruited.
For maximum results, train your athletes according to their genetic predisposition. For example, an athlete with a greater proportion of slow- twitch fibers would adapt better to running more weekly mileage and a muscular endurance program, using more repetitions of a lighter weight. Likewise, an athlete with a greater proportion of fast-twitch fibers would benefit more from sprint training and a muscular strength program, using fewer repetitions of a heavier weight.
Dit is een interressant artikel dat ik jullie niet wilde onthouden
, een paar stukjes uit het artikeltje:RECRUITMENT OF MUSCLE FIBERS
Muscles produce force by recruiting motor units (a group of muscle fibers innervated by a motor neuron) along a gradient. During voluntary isometric and concentric contractions, the orderly pattern of recruitment is controlled by the size of the motor unit, a condition known as the size principle (Henneman, et al., 1974). Small motor units, which contain slow-twitch muscle fibers, have the lowest firing threshold and are recruited first. Demands for larger forces are met by the recruitment of increasingly larger motor units. The largest motor units that contain the fast-twitch B fibers have the highest threshold and are recruited last.
No matter what the workout intensity, slow-twitch motor units are recruited first. If the workout intensity is low, these motor units may be the only ones that are recruited. If the workout intensity is high, such as when lifting heavy weights or per- forming intervals on the track, slow- twitch motor units are recruited first, followed by fast-twitch A and fast- twitch B, if needed.
There is some evidence to suggest that the size principle could be altered or even reversed during certain types of movements-specifically those that contain an eccentric (muscle lengthening) component-such that fast-twitch motor units are recruited before slow- twitch motor units (Denier van der Gon, et al., 1985; Grimby & Hannerz, 1977; Nardone, et al., 1989; Smith, et al., 1980; Ter Haar Romeny, et al., 1982). It is possible that a preferential recruitment of fast-twitch motor units, if it exists, is influenced by the speed of the eccentric contraction, and can only occur using moderate to fast speeds (Karp, 1997; Nardone, et al., 1989).
IMPLICATIONS FOR TRAINING
Training a FT -fibered muscle for endurance will not increase the number of ST fibers, nor will training a ST-fibered muscle for strength and power increase the number of FT fibers. With the proper training, FT -B fibers can take on some of the endurance characteristics of FT -A fibers and FT -A fibers can take on some of the strength and power qualities of FT-B fibers. However, there is no inter-conversion of fibers. FT fibers cannot become ST fibers, or vice versa. What an athlete is born with is what he or she must live with.
Although the type of fiber cannot be changed from one to another , training can change the amount of area taken up by the fiber type in the muscle. In other words, there can be a selective hypertrophy of fibers based on the type of training.
For example, an athlete may have a 50/50 mix of FT/ST fibers in a muscle, but since FT fibers normally have a larger cross-sectional area than ST fibers, 65% of that muscle's area may be FT and 35% may be ST. Following a strength training program for improvement in muscular strength, the number of FT and ST fibers will remain the same (still 50/50), however the cross-sectional area will change. This happens because the ST fibers will atrophy (get smaller) while the FT fibers will hypertrophy (get larger).
Depending on the specific intensity used in training, the muscle may change to a 75% FT area and a 25% ST area. The change in area will lead to greater strength but decreased en- durance capabilities. In addition, since the mass of FT fibers are greater than that of ST fibers, the athlete will gain mass, as measured by the circumference of the muscle.
Conversely, if the athlete trains for muscular endurance, the FT fibers will atrophy while the ST fibers hypertrophy, causing a greater area of ST fibers. The area of the muscle, which began at 65% FT and 35% ST before training, may change to 50% FT and 50% ST following training, The endurance capabilities of the muscle will increase while its strength will decrease, and the athlete will lose some muscle mass, again be- cause ST fibers are lower in mass than FT fibers. The decrease in mass may be observed by a smaller circumference of the muscle.
Many coaches know that, for gains in muscular strength, one should train with heavy weights and few repetitions. This training regimen works because using heavy weights recruits the FT -B fibers, which are capable of producing a greater force than the ST or FT -A fibers. Hypertrophy will only occur in those muscle fibers that are overloaded, so the FT - B fibers must be recruited during training in order to be hypertrophied (Morehouse & Miller, 1976).
Training with a low or moderate intensity will not necessitate the recruitment of the FT -B muscle fibers. Therefore, the training intensity must, be high. But how heavy a weight and how many repetitions should you use?
Muscular strength is primarily developed when an 8-repetition maximum (8RM, the maximum amount of weight that can be lifted eight times ) or less is used in a set. When the aim of training is to increase the neuro- muscular component of maximum strength, at least 95% of the athlete's 1RM and 1 to 3 repetitions should be used. When the aim is to increase maximum strength by stimulating muscle hypertrophy, at least 80% of 1RM should be lifted 5 to 8 times or until failure (Zatsiorsky, 1995).
This latter recommendation assumes that the focus of training is hypertrophy for strength, rather than hypertrophy simply for muscle size. If the aim of training is to increase muscle size (hypertrophy) with moderate gains in strength, then 6 to 12 repetitions should be used (Fleck & Kraemer, 1996). Remember, in order to improve muscular strength, FT -B fibers must be recruited.
For maximum results, train your athletes according to their genetic predisposition. For example, an athlete with a greater proportion of slow- twitch fibers would adapt better to running more weekly mileage and a muscular endurance program, using more repetitions of a lighter weight. Likewise, an athlete with a greater proportion of fast-twitch fibers would benefit more from sprint training and a muscular strength program, using fewer repetitions of a heavier weight.
