by Yuri Verkhoshanshy Edited by Jim O’Malley Editor's note : Professor Verkhoshansky is widely recognized as the world's foremost authority on speed-strength training. Introduction The author conducted a study regarding the composition and structure of the capacities that generate explosive movements, depending on the following variables : *the type of sport *the participant's age, sex, and length of sporting career *the type of muscle contraction, the type of resistance and the level of resistance *the composition and number of body components actively involved in the performance of the exercise I took into account that dynamic and isometric contractions do not exhaust all of the varieties that are possible in an approach to conditioning training - in particular the so called "combined regimen" in which the contraction is preceded by mechanical stretching of the muscles, a widely spread system in the training of many sports. When a "combined regimen" is operative, the elastic potential of mechanical muscle stretching provides an extra source of energy which enhances the subsequent muscular contraction. A muscles ability to switch rapidly from a yielding (eccentric) contraction to an overcoming (concentric) contraction by using elastic potential (accumulated during stretching) to increase the muscular contraction is commonly known as the neuromuscular systems "reactive capability". Finally, the speed-strength characteristics in controlled tasks involving overcoming (concentric) and combined (eccentric-concentric) muscle contractions appear to be closely interrelated. the overcoming (concentric) contraction is a sufficiently informative indicator of the capacity of the neuromuscular system to generate explosive force. Explosive Force Capabilities The capacities that influence explosive force applications include : * the maximal isometric muscle strength, as determined by isometric tension with no time limit * the maximal muscle strength, as displayed during explosive efforts in either isometric or dynamic performance. In the case of dynamic work, one should consider the level of resistance (which affects the specific strength displayed) and distinguish between muscular strength exerted against light, medium, and heavy resistance. * explosive muscular strength, as an indicator of the capacity to rapidly generate a maximal effort during an isometric contraction * explosive maximal strength as an indicator of the capacity to rapidly generate a maximal effort during a dynamic contraction * starting muscular strength, as an indicator of the speed at which force is generated at the start of a muscular contraction. It applies to both isometric and dynamic contractions. * accelerating muscular strength, as an indicator of the speed with which force is developed during the initial motion of a movable object. This group of component capacities appears in tasks involving explosive muscular force, independent of an athlete's specific sport, age, training age, and the type of muscular contraction. The capacities are also independent of the level of resistance, the functional specialization of individual muscles and the composition and number of body segments involved in an exercise. Predominant Factors The predominant role of one factor or another in producing explosive force depends on the level of resistance to be overcome in a particular exercise. In case of a light resistance, or during the initial speed of a movable mass, the absolute contraction speed and the starting muscular strength are of primary importance. As resistance increases, the explosive, dynamic, and accelerating muscular strength becomes more important. On the other hand, maximal isometric and explosive isometric muscular strength play a major role in the so called "starting movements" that are executed against heavy resistance. The characteristics of the general ability to generate explosive force in dynamically or isometrically working muscles are, as a rule, the first factors involved in speed-strength development exercises. However, in regard to the factorial analysis of speed-strength characteristics involved in ankle extension, it is the starting muscular strength that becomes the number one factor. This is the possible result of the ankles specific role in sporting activities because a powerful explosive effort is required of the ankle and foot in virtually all sports. The limited range of movement in the ankle joint, which results from the functional specialization of the respective muscle groups, demands the development of starting strength in the muscle groups and the ability to generate instantly effective force in a limited range of movement. Starting muscular strength is evaluated in isometric and dynamic performances. However, it must be kept in mind the isometric starting strength is a different factor from dynamic starting strength. According to Zatsiorsky and Verkhoshansky the capacity to generate maximal force in isometric and dynamic performances is generated by different neuromuscular mechanisms. The mechanisms are relatively independent of each other in their functional display and development. In dynamic contractions performed using free weights, the muscle contracts isometrically before the movement starts. As soon as the muscular force equals the amount of resistance and the movement begins, the muscle begins to contract dynamically. Resistance Levels Research data in the study of the composition and structure to generate explosive strength revealed, as expected, that the role of strength capacities when using explosive force depends on the amount of resistance to overcome. There is a link between the resistance and the capacity to rapidly generate movement against resistance. Consequently, strength increases as the amount of resistance grows. The maximal factorial weights of the speed characteristics corresponds to the optimal levels of resistance. Strength capacities can be differentiated within the range of resistances. This fact leads to the classification of power zones in the manifestation of explosive capacities and allows us to differentiate muscular force in correlation with the power zones. As the resistance increases, there are increases in performance, influenced by other factors, such as the athlete's training age, body size, strength potential and explosive and accelerating muscular strength. While the factorial composition of speed-strength characteristics for high performance and elite athletes appeared to be quite clear, the same cannot be said fro athletes in lower performance categories. Our studies indicated imbalances in the composition and structure of the capacities that generate explosive force in the first stages of systematic training. This occurs because of an uneven development of specific capacities, the absence of a clear cut training system, poor developmental sequences, and so on. It is during the advanced stages of proficiency, when the content of training becomes clear cut and specific, that the composition and structure of the capacities responsible for generating explosive force become clearly distinguished. Consequently, it is important to emphasize specific physical development as soon as an athlete has finished the all-around general developmental stage. Effective Improvement Our study also revealed that the capacities discussed above are not of equal value in generating explosive force. Depending on the requisites of accomplishing a given motor performance task, one capacity or another assumes the primary role and therefore contains the primary potential for improvement. In an integrated motor performance the individual capacities, which produce their neuromuscular mechanisms relatively independently, interact in an orderly manner to accomplish the common task. At the same time, they preserve their individuality and readiness to enter into any functional combination that may be required under the changing conditions of the performed activity. It is interesting to note that our research results failed to corroborate the frequently expressed supposition that the ability to generate explosive efforts is a synthesis. That is , a product of qualitatively blending diverse capacities, such as speed and strength, which were developed separately. Only a regimen that virtually duplicates the speedstrength primary requirements of an event can provide effective improvement. Most importantly, it should be kept in mind that the necessary functional interaction between the specific neuromuscular mechanisms required in a specific task are decisive. No other regimes or combination of regimes are an effective substitute.