Jackie Hudson, Scholar

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Jumping Articles: Abstracts and Introductions

Many athletes seek to jump higher. Typical training programs consist of resistive exercises such as plyometrics or weight training. For example, Chu (1992) recommends the plyometric exercise of drop jumping or depth jumping. Drop jumping can increase vertical jump height; however, improvement in vertical jumping due to drop jump training is widely varied and cannot be satisfactorily explained (Bobbert, 1990). In addition, plyometric training is quite stressful to the body and can produce substantial muscle soreness (Wilson, Elliott, & Wood, 1990). Thus, it is suggested that plyometric training should be added only after an athlete has established strength (Powers, 1996).

Strength training for jump sports usually consists of lifting weights for the muscles involved in jumping and/or performing Olympic lifts. These methods are accepted and widely used, yet in order to take full benefit of an increase in muscle strength, control needs to be adapted (Bobbert & Van Soest, 1994). That is, resistive exercises should be combined with or replaced by other exercises, such as repetitive jumping, that develop the technique of jumping. Such programs have been suggested for improving vertical jumps (Bobbert, 1990; Hudson, 1990).

Unfortunately, repetitive jumping may lead to injury from the cumulative trauma of landing (cf. Dufek & Bates, 1991). Repetitive jumping on the mini-trampoline, however, might minimize the trauma of landing and reduce the risk of injury. Moreover, the mini-trampoline might elicit skillful technique in jumping: First, good balance is critical to skillful jumping in that horizontal velocity must be minimized for vertical velocity to be maximized. Because the small, raised bed of the mini-trampoline offers a disincentive for jumping forward, a jumper may adjust balance automatically in order to keep sure footing. Second, better jumpers appear to use less range of motion in the crouch of the jump compared to their less skilled counterparts (Hudson & Owen, 1982). Given that part of the upward thrust in mini-trampoline jumping is provided by the recoil of the elastic bed, there is less need for the jumper to take a deep crouch. Third, skilled jumpers seem to use a more simultaneous pattern of intersegmental coordination relative to less skilled jumpers (Hudson, 1986). To be effective in jumping on the mini-trampoline, one cannot work asynchronously with the bed of the trampoline; this need to synchronize the body with the bed might lead to a relatively simultaneous intersegmental coordination. Presumably, if better technique is elicited by training with the mini-trampoline and this technique is carried over to jumping from the ground, the trainee will also jump higher.

Thus the purpose of this study was to test the efficacy of a repetitive jumping program on the mini-trampoline for improving the vertical jump. The first objective was to determine if jump height was increased after the training program. The second objective was to investigate changes in technique after the training program. Specifically, did subjects improve (a) balance by diminishing forward translation, (b) range of motion by reducing the depth of the crouch, and (c) coordination by minimizing asynchronous movement? (Article in pdf)

Vertical jumping is a fundamental motor skill which emerges in its most rudimentary form before the age of three (Wickstrom, 1983). Vertical jumping is also an important component of many complex activities such as volleyball, basketball, baseball, football, soccer, track and field, diving, gymnastics, and modern and classical dance. Consequently, vertical jumping could be taught at a variety of grade levels and at a multitude of places in the physical education curriculum. Given that most young adults, even those who compete in jumping activities, have not reached their potential in jumping (Hudson, 1986), it seems reasonable that jumping should be included more often in the curriculum. And, that when it is included, the instructor is informed about the keys to jumping skillfully.

What are the keys to jumping skillfully? Over the past several years, my colleagues and I have conducted a number of research studies of jumping. Although some of the methods and technologies we have used are not suitable for practical application, our ultimate intention has been to identify characteristics of skillful jumping that are observable by teachers and coaches as well as manipulable by performers. Even though we are still asking and answering questions, some of our results and insights may be helpful to physical educators. What follows is an illustrated overview of vertical jumping, a brief summary of our research into jumping, a prioritized list of the keys to jumping skillfully, a few simple tools of observation, and some suggestions for drill and practice. (Article in pdf)

As a general introduction to this study, let us consider the dream scenario of one biomechanist: A learner approaches the teacher and says, "I am in a slump. My free throws just don't seem to be working." The teacher responds with the suggestion that they go to the gymnasium-laboratory to investigate the problem. Once there, the learner shots a few free throws which are recorded by a measurement system that is simple, yet elegant, and capable of collecting the most pertinent information from both the subject and the object. The data are simultaneously entered into a computer that is so small that it may look like a wrist watch and so powerful that it can add the new information to the previously stored information about the learner and formulate a new strategy that is optimal (and safe) for the learner to implement. The new strategy is presented to the learner in a fashion such that it is easy to comprehend what is to be changed. The learner tries a few times to enact the strategy while these new trials are being measured and stored; and the cycle is repeated. Thus, in a span of time much shorter than that needed for trial-and-error, the learner has improved in free throw shooting and has possibly incorporated the optimal movement patterns.

Although the example given in this scenario involves a basketball player, the learner could be anyone and the skill could be anything. The concepts are equally applicable to a stroke victim relearning to walk or to a national champion swimmer endeavoring to become an international champion.

For this scenario to be possible, there will need to be cooperation and advancement in many areas. Technological help will be necessary to develop the measurement systems and computers. Sport psychologists will be called upon to answer questions about how this procedure can be used to enhance rather than detract from performance. Motor learning specialists will need to assist with ways to present the suggested improvements to the learner so that the ideas can be most readily effected. And, biomechanists will be required to determine what is optimal movement for an extremely wide range of situations - different activities, skills within activities, goals for each skill; different states of fatigue and experience; and different learner profiles with respect to strength, endurance, flexibility, body composition, and size.

The limiting factor in actualizing this scenario is the state of knowledge in biomechanics: To predict optimal movement for a variety of conditions, general theories in the techniques of movement will be necessary. But, biomechanical evolution has not reached the theory building stage. Instead, the methodological era (e.g., how to collect and reduce three-dimensional film data) is tapering off while the descriptive era is thriving. There are an overwhelming number of techniques which are as yet undescribed: consider the number of sports; the number of activities which are not sports; the number of skills within a sport (e.g., fast pitch softball has batting, base running, pitching, throwing, infielding, and outfielding); the number of purposes for each activity (e.g., high, outside, fastball; low, outside, change-up); the number of focal points (e.g., shoulder, knee, center of gravity); the number of variables (e.g., distance, velocity, acceleration, force, moment, angular velocity); and the number of populations (e.g., elite, young adult females; sedentary, elderly males; pre-pubescent girls; infant boys).

To achieve the dream scenario, it will be necessary to move beyond description to comparative studies (e.g., what is the difference between skilled and novice performers?). In this stage, the contrasts that make a difference in movement should be examined. After critical variables are identified, the effect of experimental manipulation of these variables should be studied. Finally, general theories for broad categories of movement should be developed and tested.

As biomechanical research moves into the comparative era and beyond, it should be helpful to identify variables that are powerful and comprehensive (e.g., the displacement of the center of gravity of the body, the use of stored elastic energy) and to separate technique from related, but compounding, variables (e.g., talent, training).

Three general patterns of segmental coordination (i.e., sequential [SEQ], simultaneous [SIM], and modified simultaneous [MSIM]) have been hypothesized for jumping. The purposes of this study were to describe the pattern of segmental coordination used in vertical jumping and to determine if skilled jumpers displayed distinguishing patterns of coordination. Maximum vertical jumps were performed in the counter movement (CMJ) and static jump (SJ) conditions by a heterogeneous group of 20 lean, adult subjects (s). Smoothed, digitized film records provided the data for four segments: head-arms-trunk, trunk, thighs, and shanks. For each segment the phase of positive contribution was considered to begin with initiation of extension and end with maximum angular velocity. Bisegmental and multisegmental variables were defined to assess the extent of simultaneity. Skill was determined by the effective integration of the legs (ratio of peak upward velocity of CMJ and SJ) and by the use of stored elastic energy. Although 13 s had MSIM patterns, the amount of flexion was small (< 1°) so these s were reclassified. With multisegmental analyses the number of s with SIM patterns ranged from 13 to 17; about half the time was SIM. Using bisegmental analyses all 20 s had SIM patterns; about three fourths of the time was SIM. Skilled s initiated extension and reached maximum velocity of the segments in proximal to distal order and with very small delays between adjacent segments.

INDEX TERMS: biomechanics, stored elastic energy, skill, technique, timing

In the research literature on biomechanical assessment of athletic performance, there are few studies designed to examine the performance of females with respect to males. However, a precedent-setting strategy for sex-dependent comparisons has been established in the physiological assessment of performance. According to Wilmore (1981), comparisons between the sexes should be made only if the two groups have comparable duration and intensity of training, coaching, and competition.

A theoretical aspect of the biomechanics of performance which has received recent attention is the use of stored elastic energy. Two studies (Asmussen & Bonde-Petersen, 1974; Komi & Bosco, 1978) include data for females as well as males. Since the combined results of these studies are inconclusive, the present study was designed to use the paradigm of Wilmore to investigate the performance of females with respect to males in the use of stored elastic energy.

This investigation was designed to determine if there are differences in the utilization of stored elastic energy (USEE) in the leg extensor muscles with respect to gender, skill level, and four selected biomechanical variables. Four distinct and disjoint groups of subjects were studied. There were five lean, young adults in each of these groups: 1) skilled women, 2) unskilled women, 3) skilled men, and 4) unskilled men. Film, force, and electrogoniometer records were made as each subject performed static and counter-movement jumps. The digitized film records were computer processed to obtain USEE and the biomechanical variables. The following conclusions were drawn: 1) there is no difference by either gender or skill level in USEE, 2) there is no relationship between minimum ankle angle, maximum muscular torque at the hip, or maximum downward velocity of the center of gravity and USEE, and 3) there is a negative relationship between time of concentric work and USEE.