Plyometrícs and the Brain - The Missing Dimension
Recent brain research reveals that plyometric action is not simply a phenomenon that can be adequately explained on the basis of stored elastic energy and the stretch shortening cycle. The current understanding of plyometrics is, that activities such as depth jumping produce a powerful eccentric muscle contraction that stretches the muscle, elicits a very intense stretch reflex and causes considerable elastic energy to be stored in the elongated connective tissues of the muscle complex, all of which results in an explosive concentric counter-movement.
While this explanation is correct, the phenomenon of plyometrics involves far more intricate processes than reflexive muscle activities that operate at the level of the spinal column and bypass the brain. Many of the subtleties and complexities of plyometrics can be missed if one is preoccupied with the prescription of so called plyometric drills or with the laboratory measurement of the stretch-shortening cycle.
In both cases, it is easy to overlook the possibility that activities such as depth jumping or medicine ball throwing may involve non-local events, particularly the enormously complicated computer programs located in the brain. While it is accurate to state that plyometric actions are extremely rapid and therefore occur at the level of specific spinal nerves without involving conscious thought processes, it must be remembered that the preparatory period prior to the plyometric action can involve a higher order of mental processing composed of exceptional intricacy. In fact, the period prior to execution of any skilled movement involves running mental programs that have been stored and refined by repeated rehearsal in the brain of the well-trained athlete.
To appreciate the scope of plyometrics, it is necessary to distinguish clearly between plyometric actions, which occur as part of many running, jumping, striking and other rebounding movements in sport, and plyometric training, which applies plyometric actions as a distinct training modality according to a definite methodology (defined in Siff & Verkhoshansky, Supertŕaining, 1993). One can distinguish further between a plyometric action produced under conditions in which the athlete anticipates a particular course of action (cognitive plyometrics) and a plyometric action produced as a purely reflexive response under unexpected circumstances (non-cognitive plyometrics).
The latter type of plyometrics occur primarily under survival or self-preservation conditions intended to protect a person from injury or death. The rapidity of the event does not permit any forethought or planning, but relies on primitive reflexes that generally tend to bypass the brain by acting at the more spontaneous level of the spinal cord (Fitness and Sports Review International, 29-364, 1994,129). Cognitive plyometrics, though also a very rapid phenomenon, is preceded by a phase of thinking that prepares the person for a specific course of action to achieve a definite goal.
One should not conclude simplistically that noncognitive plyometrics are purely instinctive or automatic actions which involve no cognitive or learning processes. It should never be forgotten that efficient execution of plyometric actions and drills only takes place after a considerable amount of practice using cognitive processes. In fact, most athletes do not manage to perfect many plyometric skills even after many weeks of practice. The use of numerous sequential repetitions to imprint these skills may constitute the inappropriate strategy because classical plyometrics are 1RM movements which require as much as several minutes of rest before recovery is complete.
Sub-maximal plyometrics and pseudoplyometrics (Siff & Verkhoshanksy, 1993) may be performed in a state or advancing fatigue, unlike classical "shock method" plyometrics. The neural and reflexive processes are quite different in each case. Even then, what appears to be quite reflexive still involves a certain degree of cognitive preparation and control. The lack of adequate mention of the importance of cognitive and learning processes in plyometrics by all popular texts on the subject constitutes a major deficit in the field. Reflexes are casually referred to as entirely robotic actions that elicit or inhibit muscle contraction, but little is mentioned of the fact that reflexes can be trained and modified, something that the renowned Russian physiologist, Pavlov, had proved some 70 years ago in the form of his "conditioned reflexes."
Later, Skinner (1938) distinguished between two types of conditioning, which he called respondent conditioning, in which the response is modified by a preceding stimulus, and operant conditioning, in which the response is strengthened or weakened by events that follow the
In the plyometric situation, this implies that a stimulus such as an emotion (e.g. fear, excitement) or a mental image (or visualization), that entertains before an action like a depth jump, can shape the subsequent neuromuscular reflexes. Likewise, any event (such as the jarring of the body, post movement fatigue or an injury) following a plyometric action can modify these reflexes. In fact, it is common for plyometric activity to be associated with both respondent and operant conditioning. It has also been shown that if the reflex learning process is carried out with the subject in a particular physiological or psychological state, then the conditioned reflexes are exhibited only when the same state is present, but not when the state is different. This phenomenon is known as state dependent learning. Its existence implies that plyometric proficiency or deficiency learned in a specific training situation may not be reproduced under competitive circumstances which differ from those of the learning situation. What the preceding few paragraphs imply is that it is only partially correct to regard plyometrics as a process in which basic reflexes automatically produce a powerful muscle contraction which is accompanied by elastic energy released after the muscle has been stretched eccentrically (130, Fitness and Sports Review International, 29-3&4, 1994). It is vital to note that the entire plyometric process involves complex state-dependent learning events which modify the pattern of reflex activity
according to how the given plyometric drills are executed.
This may be one of the reasons why some researchers have carried out experiments which apparently have shown plyometric training to produce little or no improvement in speed strength or sporting performance. One cannot ignore the neural factors involved in studying the effects of any neuromuscular phenomena, the study of muscular output alone is incomplete and lack of control over essential neural factors affecting the experiment can easily distort the results. Further understanding of plyometrics may be gained by recalling the difference between co-contraction and ballistic actions. In contracting actions, agonist and antagonist muscles contract simultaneously, with dominance of the former producing the external motion. Ballistic actions involve bursts of muscular activity followed by phases of relaxation during which the motion continues due to stored limb momentum. The term "ballistic" (as in projectile motion) is used, since the course of action of the limb is determined by the initial agonist impulse, just as the flight of a bullet is determined by the initial explosive charge in the cartridge.
Skilled, rapid ballistic and moderately fast continuous movements are preprogrammed in the central nervous system, whereas slow, discontinuous movements are not. The ballistic action rarely involves feedback processes during the course of a movement. Feedback from the muscles and joints to the central nervous system permits the ensuing motion to be monitored continuously and to be modified, if necessary. The resulting movement becomes accurately executed and the relevant soft tissues are protected from injury by changes in muscle tension and by the activation of appropriate antagonists to control and terminate the motion.
If no sensory or proprioceptive feedback is implicated, the mode of control is termed, feed forward or "open-loop" control (Siff & Verkhoshansky, Supertraining, 1993). Here, control is preprogrammed into the central nervous and neuromuscular systems by the visual and auditory systems before movement begins, so that ongoing monitoring mechanisms are not
The first sign of impending garnered action is the inhibition of antagonist contraction preceding agonist action, as revealed by the electromyograph. Premature activation of the antagonists may not only diminish skill, but it can cause muscle damage during ballistic and other rapid movement, antagonist contraction is appropriate only to terminate further motion of the limb concerned.
Not only is there no antagonist activity during ballistic movements, but it is also absent during discontinuous motion (Brooks, 1983). The advantage offered by feedforward processes is speed of action, whereas its main disadvantage is the lack of flexibility which can be offered by feedback. Nevertheless, the importance of feed forward processes in human movement should not be underestimated, as implied by the Russians in using regimes of visualization and autogenic training in sports preparation (Fitness and Sports Review International, 29-3&4, 1994). This analysis of ballistic and reactive actions reveals that cognitive and non-cognitive actions both involve ballistic movement, since an initial explosive action produces projected (i.e. ballistic) motion of the body or a given limb. Thus, if any cocontraction of agonist and antagonist occurs during the propulsion phase, the action should be deemed to be non-plyometric. This is common during many of the slower jumping and medicine ball drills that are called plyometric by their popularity, but are actually pseudoplyometrics, whose training effectiveness has much more to do with rapidly terminated eccentrics than any true plyometric action. It is not often appreciated that ballistic movements require considerable planning in the brain. Slow or co-contractive movements permit adequate time for improvisation and correction of the ongoing process by response to feedback. Consequently, a thorough mental plan of action is not required before this type of movement occurs.
On the other hand, for sudden limb actions lasting less than about 0.2 second, feedback correction is invariably futile because reaction times are too long. Ballistic action requires the brain to estimate every detail of the movement in advance via feed forward processes. The pattern of movement, the force of propulsion, balancing by the stabilizing muscles, the duration of the propulsive phase, the relative positions of all links of the body and the positioning of all links of the body after the movement are some of the many details that have to be preprogrammed into the brain.
It should be more obvious now that plyometric training is not simply a matter
of dropping from a height or throwing an object for a given number of repetitions to improve fitness qualities such as strength speed or explosive strength. Sport usually involves the reproduction of a wide variety of technical skills under expected and unexpected conditions, so that feed forward training and other "visualization" (mental and kinesthetic imaging) techniques must be used to enable the athlete not only to increase explosive strength and strength speed, but also to efficiently manage any plyometric actions under real sporting conditions. Lest the connection between visualization and movement be oversimplified by sports psychologists, neuroscientist, Dr. Kensall Wise of the University of Michigan, points out that the part of the brain which can visualize a given action is totally separate from those parts which initiate the muscle contractions to carry out the action (Scientific American, Oct 1988: 23).
Although fairly modern research has identified some of the connections between some regions of the brain and functions such as sight, hearing and motor output, researchers still have only a vague idea of how the nervous system initiates and manages any given actions. The importance of ballistic activity to humankind recently has been shown to extend far beyond the realms of sport. Neurophysiologist, William Calvin, has proposed the fascinating hypothesis that the brain’s planning ballistic movements may have played a major role in the development of language, music and intelligence over the ages (Scientific American, Oct 1994). He makes this proposal, since ballistic movements and language processes, (132 , Fitness and Sports Review International, 29-3554, 1994) some of the same regions of the brain, in particular those associated with sequencing and planning. In reaching this conclusion, he emphasizes that ballistic movements, unlike cocontractìve slower movements, require a great amount of planning and problem solving.
Slow movements may be corrected readily by ongoing feedback information, but ballistic movements require the brain to determine every detail of the action in advance by mentally planning the exact sequence of neural activation for numerous individual muscles. Apparently, parts of the language cortex of the brain serve a far more generalized function than previously suspected. It is implicated in the production of novel sequences of sensations and movements for both the hands and the mouth, so that ballistic arm actions may play a role in mental development. Calvin adds that in language, skills might improve dexterity and vice versa.
The importance placed by Russian coaches on their athletes being able to accurately describe, draw and visualize sporting movements would appear to correlate with this proposal. Instead of simply carrying out entertaining plyometric drills like biological robots, our athletes would be well advised to integrate cognitive processes more actively into the training program.
Originally Posted in Soviet Sport Review 1994