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Fast-twitch for a fast-pitch!

Baseball pitching is a skill requiring varying degrees of velocity, depending on the type of pitch thrown.  The trunk and lower body contractile forces provide more than 50% of the power needed by the upper body to produce the pitch.  The requirement on a contractile level for the upper and lower body musculature is that the force be great with a fast rate of force production.  The fiber has to be able to handle quick ATP-PC resynthesis. Fast-twitch fibers are the fiber of choice.

Specificity of training for a baseball pitcher means exercising in a highly specific way for the physiological components that are expressed through:

  • characteristics of fiber-types
  • fiber recruitment patterns
  • velocity and rate of force production

The information presented can give you a scientific basis for making decisions about a strength, power, and cardiovascular program appropriate for a pitcher.

To stimulate further thought on your part, the following two issues have been included:

fiber composition of power athletes the problem with inappropriate non-specific training

All information is referenced by statement for your further investigation.

Baseball pitching is an overhead throwing motion that is performed in less than a second in an explosive and ballistic manner.

Training a baseball pitcher for improvement of performance involves the process of systematic and progressive exercises that challenge his current state of adaptation with regard to power.

It is important to keep in mind this pertinent and important scientific formula: power = strength + speed.

Characteristics of fiber-types

The brain outputs information to the skeletal muscles, with the result being a contractile force.  The metabolic demand of the movement and the required intensity of the movement dictate the recruitment of the motor units that will produce the contraction; the force production capability and rate of recruitment are characteristic of the different fiber-types.

A motor unit is the functional unit of neural control for muscular activity.  Motor units consist of a cell, an alpha motoneuron, and all the muscle fibers innervated by the alpha motoneuron.  Within a motor unit, all the muscle fibers have nearly identical biochemical and physiological properties (Brooks, 2000).  However, there are differences between motor units which result in functional differences in their contractile properties; namely, force capabilities and speed of contraction.

Histochemical and Physiological Fiber Differences

From a histochemical perspective,  the fibers are distinguishable on the basis of differences in myofibrillar-ATPase activity.  The ATPase activity reaction correlates with speed of contraction; fibers with low ATPase activity are ST (slow-twitch or type 1) and those with high ATPase activity are FT (fast-twitch or type 2a and 2b) (Gollnick, l972).  The FT demonstrate a high maximum velocity of shortening and under isometric conditions, require a short time to reach peak tension. Conversely, the ST fibers possess a slow velocity of shortening and long time to reach peak tension.  Slow twitch are fatigue-resistant, fast-twitch are fast-fatigable (2a are fast-fatigue resistant, i.e., properties of both 1 and 2a) (Gollnick, l972).

Histochemical studies also reveal differences in a fiber’s metabolic characteristics by identifying its reaction for succinic dehydrogenase (SDHase).  A fiber with a strong reaction is interpreted to be an oxidative fiber, and a weak reaction is associated with a nonoxidative or glycolytic metabolism. SDHase activity studies reveal a correlation with ATPase studies in terms of fiber-type characteristics; ST are oxidative and FT are nonaerobic and glycolytic (Brooks, 2000).

Physiological studies of the myosin component of the muscle indicate that it plays a special role in the contractile characteristics of the muscle.  The myosin heavy chain (MHC) appears in three different varieties or isoforms, type 1, 2a, and 2b, as are named the muscle fibers that contain them.  These myosin molecules make a difference in the force generation capacity of the cross-bridges of the three fibers.  Type 2b fibers contract approximately 10 times faster than type 1 fibers, with the contraction velocity of 2a fibers lying intermediate to 1 and 2b’s. Fast motor units also produce 100 times more force than slow motor units.  The difference is velocity of contraction is due to the size of the axon (Henneman, 1964) and the difference in force-production capabilities is due to the cross-sectional area of the muscle fiber.  The FT possess a greater cross-sectional area than the ST.
Recruitment Patterns

Through the examination of glycogen depletion patterns of exercising muscle, different patterns of use and metabolic modes for the fiber-types were demonstrated.  During bicycle exercise at various loads requiring 60 to 80 % of maximal oxygen uptake, Gollnick, et al., l973, found that type 2 fibers depleted sooner and more completely during the sprint bouts, and the type 1 fiber depleted sooner and to a greater extent during the endurance exercise. Gollnick, l974 also found a preferential recruitment pattern with type 1 fibers being recruited regardless of exercise intensity, and the type 2 fibers being recruited during higher intensity powerful efforts or during prolonged activity to fatigue.  This suggests that type 2 fibers are preferentially recruited for the performance of short, high-intensity work bouts.  Vollestad, l984 confirmed these findings in a similar study.

The principle of an orderly recruitment of single motor units (Henneman, l964) was derived from an investigation using slow increasing voluntary muscle contractions.  The theory states that ST fibers are always recruited first, regardless of force.  Desmedt, l978, investigated the behavior of motor units during ballistic contractions.  They found no difference in the discharge pattern of motor units during self-paced ballistic contractions; nor was there a difference in firing patterns between fast and slow-twitch dominant muscles.  The principle of an orderly recruitment pattern holds true, regardless of force or time to peak force.

Fast-twitch fibers and power

Fiber-type composition and the proportion of fast twitch fibers play an important role in power-speed related sports.  The higher the proportion of fast-twitch fibers, the quicker and more powerful the contraction. The ability to change a type of muscle fiber to another as a result of training is critical for gains in strength, and still a topic of much controversy.  Recent studies suggest that a shift in fiber type may be possible as a result of prolonged, high-intensity training.  The long-term adaptation seems to result in some conversion of slow twitch to fast twitch and there is a proportional increase in fast twitch as the expense of slow twitch (Jacobs, et al., l987 and Abernethy et al., l990).  Dynamic strength increases relative to muscle cross-section have been positively correlated to the relative content of type 2 fibers (Dons, l979).

A high percentage of type 2 fibers would be advantageous for power-type athletes.  At any given velocity, the torque produced is greater the higher percentage of distribution of type 2 fibers (Foss, l998).  This is due to their ability for a faster rate of tension development related to the contractile dynamics of ATPase activity and calcium release and uptake from the sarcoplasmic reticulum.

Fiber-composition and power athletes

Examination of differences in muscle fiber-type distribution  among  athletes involved in various sports found  jumpers and sprinters to have the highest percentage (61%) of fast-twitch fiber distribution.  Olympic lifters and power lifters were also found to possess FT fibers which are two times larger in diameter than the ST fibers of the same muscle (Prince, 1976).

When measured, the untrained group displayed 56% of fast-twitch fiber distribution as compared to the trained group of 61%. This is not to imply that their power or maximum strength would be equal.  If the two groups were tested in both power or maximum strength, the difference in their capacity would be very large.   It is to imply, however, the possibility that training can significantly increase the ability to display power and maximum strength (Golnick, et. al., l972, Costill, et. al., l976, Komi, et al, l977.

Training the power fibers

Power refers to the ability of the neuro-muscular system to produce the greatest possible force in the shortest period of time. Power is the product of force (F) and velocity (V) of movement (P=F x V).  For athletic purposes, any increase in power must be the result of improvements in either strength or speed, or both. The goals of training for power must be to: (Hakkinen and Komi, l983)

  • improve the amount of force at a given rate
  • improve the rate of that force production
  • improve intramuscular coordination between excitatory and inhibitor reaction
  • Improve the speed of contractio

Although it has been suggested that power athletes possess a greater percentage of FT fibers, the available data does not confirm this.  However, there is a potential for growth of FT fibers allowing the area of muscle occupied by FT fibers to increase to 90%, regardless of a starting fiber-type composition within the normal range. This is valuable information in that there is evidence that a high percentage of FT fibers is advantageous in power-oriented events ( Tesch, l988) due to their increased capacity for quick and forceful contractions.

In l987, Jacobs et al., conducted a study to determine the effects of sprint training on histochemical and enzymatic adaptations of the muscle fiber-type.  In a six-week study, subjects exercised 2 to 3 times weekly with 15s and 30s “all-out” sprints on a cycle ergometer. The number of sprints was increased from two each during weeks 1 through five to six each during week six.  The results of the study showed a % increase in FT fibers from 31.9% +/- 8% to 39.1% = +/-8% (P=0.008).  There was an associated decrease in ST fibers from 57.7% +/- 16.6% to 48.3% +/- 9.3 (P=.087).

Hakkinen, Komi, and Tesch (l981) conducted a 16-week study of combined concentric and eccentric strength training.  Loads of 80 to 100% 1 RM for concentric, and l00 to 120% 1 RM for eccentric were utilized.  The training caused significant improvements in maximal force and various force-time parameters.  These findings were accompanied by internal adaptation in the trained muscle due to increases in the areas of the fast-twitch muscle fibers.  These findings were in agreement with previous findings of increases in performance (Sale, l986) through strength training.  Neural changes occur through training which help the individual muscle to achieved greater performance capability.  This was achieved by shortening the time of motor unit recruitment, especially FT fibers, and by increasing the tolerance off the motor neurons to increased innervation frequencies (Hakkinen and Komi, l983).

The problem with inappropriate training

In l982, Bosco found that indiscriminate use of training methods that hypertrophy both slow and fast twitch fibers can impair the invaluable role played by FT development.  Development of ST fibers appear to provoke a damping effect on FT contraction during fast movement.  This is due to the fact that during high speed shortening of muscle, the sliding velocity of ST fibers can be too slow and may exert a damping effect on the overall muscle contraction.  He concluded that the central role played by the storage and release of elastic energy by the connective tissues of the muscle complex should never be ignored in sport specific training programs.*
* This comment makes reference to the SEC which exerts force when an actively contracted muscle is stretched.  There is a considerable storage of energy in the SEC since an actively contracted muscle resists stretching with great force, particularly if the stretching is imposed rapidly.  This resistive force, exerted at the extremities of the muscle, and not the direct lengthening of contracted muscle, is responsible for the storage of elastic energy within the SEC.

Low-volume high-intensity resistance exercise increases the cross-sectional area of fast and slow twitch fibers, with a greater relative hypertrophy occurring in the FT fibers (McDougall et al, l980, Tesch et al, l983, Thorstennson, l976.  Tesch et al (l987) showed that a six-month long heavy-resistance training resulted in a decrease in the activity of enzymes involved in glycolytic and aerobic metabolic pathways (hexokinase, citrate synthase, myokinase nd phosphofuctorkinase).  Additional  research revealed that citrate synthase activity is lower in weightlifters and powerlifters compared to bodybuilders, non-bodybuilders, and non-athletes (Tesch, l988).  This difference is probably due to the fact that bodybuilders train at moderate intensity and fairly high volume.  Five months of heavy resistance exercise was also shown to significantly increase the levels of the energy substrates glycogen, ATP, creatine phosphate and creatine (MacDougall et al, l977).

Moderate intensity, high repetition resistance exercise, as commonly used in circuit training ( a popular mode among pitchers) can convert FT to behave more like ST fibers, apparently in an adaptive attempt to resist the fatigue of the repeated efforts (Timson et al, l985, Baldwin et al, l992, Noble & Pettigrew, l989 . The mechanism for this muscle adaptation was offered by Hoy et al (l980) who found that the fast isoforms of myosin disappear and are replaced by isomyosins that are characteristic of slow muscle after Moderate intensity, high repetition resistance exercise, as commonly used in circuit training ( a popular mode among pitchers) can convert FT to behave more like ST fibers, apparently in an adaptive attempt to resist the fatigue of the repeated efforts (Timson et al, l985, Baldwin et al, l992, Noble & Pettigrew, l989 . The mechanism for this muscle adaptation was offered by Hoy et al (l980) who found that the fast isoforms of myosin disappear and are replaced by isomyosins that are characteristic of slow muscle after chronic overloading.  This fiber transformation caused by chronic stimulation is regulated primarily at the genetic transcriptional level of regulation (Heilig & Pette, l983). This process is confirmed by the presence in FT muscle of a myosin light chain component that is usually observed only in ST fibers (Samaha et al, l970).

The take home message is that training programs can produce different outcomes.  Knowing the desired objective and using scientific principles as a basis is crucial and necessary in order to not only improve performance, but to do no harm.

For the scientist:

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Costill, D., J. Daniels, W. Evans, W. Fink, G. Krahenbuhl, and B. Saltin.  Skeletal muscle enzymes and fiber composition in male and female track athletes.  J Appl Physiol, 40:149-154,1976

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Gollnick, P., R. Armstrong, B. Saltin, C. W. Saubert IV, W. Sembrowich, R. E. Shepherd.  Effect of training on training on enzyme activity and fiber composition of human skeletal muscle.  J Appl Physiol, 34(1):107-111,1973.

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Hakkinen, K., P. Komi and Per Tesch.  Effect of combined concentric and eccentric strength training and detraining on force-time, muscle fiber and metabolic characteristics of leg extensor muscles.  Scand.  J. Sports Sci., 3 (2): 50-58, 1981.

Henneman, Elwood.  Relations between structure and function in the design of skeletal muscles. Journal of Neurophysiology, 28, 581-598, l965.

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