MUSCLE-CONTRACTION PROPERTIES IN OVERARM

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Journal of Strength and Conditioning Research, 2006, 20(1), 117–123 q 2006 National Strength & Conditioning Association

MUSCLE-CONTRACTION PROPERTIES THROWING MOVEMENTS

IN

OVERARM

APOSTOLOS K. GREZIOS,1 IOANNIS TH. GISSIS,1 ARISTOMENIS A. SOTIROPOULOS,2 DIMITRIOS V. NIKOLAIDIS,3 AND ATHANASIOS G. SOUGLIS2 Laboratory of Biomechanics, Department of Physical Education and Sport Sciences, Aristotelian University of Thessaloniki, Thessaloniki, Greece; 2Department of Physical Education and Sport Sciences, University of Athens, Athens, Greece; 3City College of Thessaloniki, Thessaloniki, Greece. 1

ABSTRACT. Grezios, A.K., I.Th. Gissis, A.A. Sotiropoulos, D.V. Nikolaidis, and A.G. Souglis. Muscle-contraction properties in overarm throwing movements. J. Strength Cond. Res. 20(1):117– 123. 2006.—On the basis of dynamic and kinematic data, this study identifies the type of muscle contraction in unloaded overarm throwing movements. An unloaded throw or nearly unloaded throw is defined as the throw in which the external resistance is too small (e.g., the team handball, baseball, and water polo throws as well as the tennis and badminton smashes). A special arm-force–measuring apparatus was constructed to imitate an overarm throw. Forty-two subjects were placed into 3 groups: untrained subjects, weight-trained athletes, and team handball players. The measured parameters included the velocity of the initial movement, the release velocity, the velocity of the first 50 milliseconds of the concentric phase, the force value at the moment of deceleration of the initial movement, and the impulse values during the eccentric and concentric phases of the test movement. Statistically significant higher values of the above parameters (p , 0.05) were determined in that test at which the initial speed of movement was higher. Also, the correlation coefficients of the parameters of the initial phase of the throw movement were very high (p , 0.001), especially the parameters related with the movement’s first 50 milliseconds. The results support the thesis that the stretch–shortening cycle is the type of muscle contraction in unloaded overarm throws. Furthermore, it is possible to increase the throw velocity by increasing the velocity of the initial movement (i.e., by provoking higher inertia forces). KEY WORDS. initial force, stretch–shortening cycle, overarm throw velocity

INTRODUCTION enerally, it is accepted that the stretch–shortening cycle (SSC) represents the type of muscle contraction present in jump movements (5, 6, 18, 19). This type of muscle contraction is unique and its efficiency depends on neural factors (13). Despite the jumps, the SSC is not considered self-evident in overarm throwing movements. For example, Mu¨ller (28) states that during the initial movement in the javelin throw the passive musculature is mainly stretched because of the activity of the antagonist muscles. The overarm throwing movements are therefore accomplished through a relaxed muscle activation status, and the throw velocity depends on the subject’s voluntary recruiting ability. From the biomechanical point of view, the movendum or the system hand movendum forms the last joint of the kinematic chain, which, in most throwing movements, has its beginning at the thrower’s contact point with the ground, with the exception of the throw in water polo or the jump overarm throws. (The term movendum

G

implies the object, whether the game ball or the athlete’s own body, that must be moved in a specific situation in order to complete an action or a movement [12, p. 87].) In this case, the distal joint throw velocity of the kinematic chain can be described with the formula Vend 5 VAnf 1

OV

Gel/di i

,

where VAnf designates the absolute speed of the first joint in the chain and VGel/di i is the relative velocity of the following joint in relation to the proximal joint (36). If one regards this formula purely mathematically, then a maximization of each term on the right leads to a maximization of the throw velocity (Vend). However, muscle-power development is not arbitrarily variable but possesses a characteristic that determines its development and maximum force value. Stucke (32) reports that the efficiency of its effect depends on forces that are produced from the movement itself. Such forces could develop with the described initial and acceleration procedures. In sport training practice, it is reported that the musculature involved in the throw disciplines is prestretched before the acceleration phase (20, 34), which is related to the implementation of the principle of initial strength (16). In published works concerned with the kinematic description of overarm throws, no clear statements exist about the presence and the extent of a muscle stretch. The total period of the overarm throw movement amounts to a maximal 120 milliseconds. In a kinematic chain, muscles are sequentially activated (15). This sequential activation is very important for the ‘‘inertia timing’’ (22). Therefore, for each muscle, the activation time amounts to only a fraction of the total throw time (9, 11, 17, 26, 27). If a time period of 130–140 milliseconds is regarded as essential for maximum voluntary activation (28), then voluntary physiological processes cannot account for the high speed and energy values in the time period between 20 and 40 milliseconds. These procedures rather resemble the stretch behavior of muscle preparations in such a way that greater attention would have to be devoted to the effects of the elastic muscle characteristics. If one considers the tension behavior of an activated muscle, the biomechanical principle of the initial strength can become invalid, as initial forces can be achieved by deceleration of the initial movement and by stretching an activated muscle (2). In both cases it must be presupposed that the musculature is already activated. In overarm throws, the muscle stretch can be caused both by the deceleration of the initial movement and by the effect of the forces of inertia, which, especially for the distal segments,

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ET AL.

movement program is adapted to the respective individual training condition. An increased preactivation level enables the muscle to compensate for larger stretch loads and, in addition, to store more elastic energy in the context of SSC. The above-mentioned considerations raise the following hypotheses: (a) differences in the initial force and throw velocity values are positively correlated with the acceleration process of the initial movement, and (b) the execution of the initial movement in overarm throws is determined by the respective training level and is part of the movement program. If this part is consciously manipulated, then the success of the throw worsens. The initial force level cannot be increased arbitrarily (maximization), but it must be on an optimum level that corresponds to the training level (optimization). FIGURE 1. The measuring station. The subject’s hands smoothly touch the mobile part where the force-measuring elements are placed. The subject applies a negative acceleration to the mobile part (initial phase) and then accelerates the force-measuring element-carrier forward. The mobile part falls on a mat. Directly before the mat, 2 light barriers are placed that indicate the subject’s release velocity. Thus, the subjects are motivated to try to exceed their previous velocity value.

can reach relatively high values. These characteristics of muscle stretch were considered in the model of Tutjewitsch (33), where the variant of cooperating was sought within a spring-mass system in which each spring was at its most beneficial starting position at its activation. In reverse analogy to real conditions—in the model the effect of muscle contraction (shortening) is reached by stretching the appropriate spring—this most beneficial starting position was reached by a strong reduction of the spring’s length through the stretch of the previous spring. On the contrary, in drop jumps, for example, the stretch load in overarm throw movements is produced by the subject’s antagonist muscles. In accordance with the principle of initial strength, one must expect higher initial forces (larger deceleration) and presuppose more intensive work of the antagonist muscles (velocity of the initial movement). As mentioned earlier, the impact throw movements are carried out within a very short time. Thus, the effect of voluntary activation processes can be excluded during the course of motion. Therefore, the SSC takes place under conditions that are given from the beginning of the movement. Because a passive muscle does not exhibit elastic characteristics, it must be preactivated during the throw to a certain degree. Preactivation is determined by the central nervous system (CNS) and regulates muscle stiffness. Because this regulation can take place before the beginning of the movement, one can assume the grade of preactivation is part of the movement program. The observation that trained persons exhibit higher preactivation electromyographic potentials than do untrained persons (13) permits the assumption that this part of the

METHODS Experimental Approach to the Problem

For the purpose of measuring, a special arm force–measuring apparatus (Figure 1) was developed, which is described in the following paragraphs. The apparatus simultaneously allowed the simulation of the overarm throw movement and the recording of its kinetic and dynamic characteristics in a laboratory setting. To examine the effect of the level of training of an athlete’s overarm throw movement, we used team handball players, weighttrained athletes, and untrained persons as subjects. Handball players were highly accustomed to overarm throwing because the action is inherently part of the sport. During the measuring of the characteristics of the movement, these athletes were in the middle of their training season; therefore, their training was geared toward sustaining their levels of strength. Furthermore, their overarm throw ability was enhanced through sportspecific training. The weight-trained athletes were chosen because of their high level of muscle strength. At the time of the study, these athletes were training to increase their muscle mass; however, none were familiar with the mechanics of the overarm throw movement. These subjects were chosen to find out which parameters of the movement, if any, were dependent on muscle strength alone and were not a result of familiarity with the mechanics of the movement. Subjects

Forty-two subjects participated in the study and were placed into 3 equally sized groups: group 1 5 untrained subjects (sport students), group 2 5 weight-trained athletes, and group 3 5 team handball players. Group 1 subjects were not exposed to situations that could affect the coordination or strength of the overarm throw in any way, both in their daily life as well as in their leisure activities. Group 2 served as a reference group for the isometric maximum force. Group 3 consisted of team handball players who played in the highest national league (Table 1). For all groups, the measurements occurred during the winter months, which ensured the subjects were in very

TABLE 1. Average values (mean 6 SDs) of the anthropometrical characteristics of the sample population. Group

n

Age (y)

Height (cm)

Weight (kg)

Untrained subjects Weight-trained athletes Team handball players

14 14 14

27.8 6 3.6 26.4 6 2.5 24.2 6 3.6

180 6 3.4 186 6 4.2 192 6 3.5

79.3 6 5.2 105 6 5.6 88.6 6 2.2

MUSCLE-CONTRACTION PROPERTIES IN OVERARM THROWING 119

FIGURE 2.

Schematic representation of the test position.

good training condition. The Ethics Committee approved the study, and all subjects signed written informed consent before participation. Description of the Measuring Station

The measuring station consists of 2 force-measuring elements, a seat, a rope-length giver, and a mobile part. Each subject sits on the seat with his or her arms nearly stretched and hands easily affecting the surface of the force-measuring elements (Figure 2). The seat face can vary in height, which enables each subject to assume the correct position. To avoid overstretching, a broad leather belt holds the test subject on the chair. Description of the Test Movement and the Raised Parameters

For the examination of the formulated hypothesis, the subjects carried out 2 throws. In the first test (throw 1), the initial movement was executed at the subject’s selfselected velocity. In the second test (throw 2), the subjects tried to execute the initial movement as fast as possible. In each test, the best 1 of 3 accomplished attempts was considered in the statistical analyses. From the force-time curves, the following parameters were computed: kinematic (Vinit 5 velocity of the initial movement [inertia forces and thus the extension load], Vend 5 velocity at the end of the concentric phase [throw velocity], V50 5 velocity after the first 50 milliseconds of the concentric phase), dynamic (Fo 5 initial strength [the force value at the reversal moment, with initial velocity equal to 0]), and impulse (Iinit 5 impulse from the beginning of the initial movement up to the time of the maximum drawing-back velocity, Idecel 5 impulse of the deceleration phase from the time of the maximum drawing-back velocity up to the point of reversal, I50 5 impulse of the first 50 milliseconds of the concentric phase, Icph 5 impulse of the concentric phase). Figure 3 illustrates the force-time, way-time, velocitytime, and integrated force-time curves of the test. Between time points t0 and t1, the initial acceleration of the mobile part (drawing-back movement) takes place. At the time point t1, the initial velocity reaches its maximum value, whereas the force of negative acceleration is equal to 0. At the time point t1, the deceleration of the inertia forces of the mobile part begins; this corresponds to the eccentric phase of this test movement. At the time point t2, the initial movement is completed. At this time the initial velocity is equal to 0 and the force reaches its maximum value. The maximum force value corresponds to the initial force (Fo) with which the concentric movement defined by the time points t 2 and t3 is accomplished. At the

FIGURE 3. Exemplary representation of (a) the force-time curve, (b) the integrated force-time curve, (c) the way-time curve, and (d) the velocity-time curve. The time point t0 is the beginning of the initial movement, t1 is the time point of the maximum negative acceleration and the beginning of the deceleration phase, t2 is the reversal time point and the beginning of the concentric phase, and t3 is the end of the overarm throw.

time point t3, the mobile part is no longer accelerated and the throw velocity reaches its maximum. Measuring Accuracy and Error Estimation

To measure the coincidental error, the curves of 15 attempts of 3 different persons were evaluated. The maximum relative evaluation errors lay between 0.6 and 1.2%. For the examination of the reliability at a number of 15 subjects, the same test (constant stretch amplitude, speed, and acceleration) was executed twice, with 1 week between the tests. Each subject completed 3 repetitions, the best of which was evaluated for the calculation of the reliability coefficient. The reliability coefficient values lay between 0.93 and 0.95. Data Collection

The force was registered from 2 quartz crystal force-measuring elements of the Kistler company (type 9351A). The measured forces were amplified by a charge amplifier (type 5041) of the same company. The registration of the space-time characteristics occurred with a special ropelength giver (type SGG 300). Velocity-time signals were brought out with the electrical differentiation of the space-time characteristics. The angle-time curves were registered with an elec-

5.45 6 1.2 8.86 6 1.83 0.60 6 0.12 0.96 6 0.18 5.23 6 0.37 5.9 6 0.47 163.5 6 57.2 232 6 60.21 13.48 6 4.44 19.28 6 5.03 1.12 6 0.26 1.54 6 0.34 Group 3 Throw 1 Throw 2

12.32 6 2.9 16.87 6 3.73

9.98 6 4.85 14.02 6 6.64 0.86 6 0.18 1.36 6 0.46 5.08 6 0.23 5.73 6 0.39 199 6 62.8 316.5 6 124.58 15.5 6 10.2 26.35 6 16.61 0.94 6 0.30 1.76 6 0.68 Group 2 Throw 1 Throw 2

10 6 3.09 22.88 6 10.96

0.55 6 0.23 0.88 6 0.24 4.76 6 0.28 4.56 6 0.49 100.15 6 26.13 196.7 6 67.5 8.15 6 4.19 15.17 6 6.70 5.75 6 2.37 11.15 6 3.09 0.55 6 0.23 1.15 6 0.34

I50 (nm) V50 (m·s21) Fo (N) Idecel (nm) Iinit (nm) Vinit† (m·s21)

TABLE 2. Average values (mean 6 SDs) of the 3 groups during the free-throw execution.*

Table 2 depicts the average values and SDs of the drawing-back speed, the impulse of the drawing-back phase, the deceleration impact, the initial force, the terminal velocity, the impulse of the concentric phase, and the speed and impulse values during the first 50 milliseconds of the concentric phase of the 3 groups during the free-throw execution. The drawing-back speed corresponded to individual feeling in throw 1 and was maximally negatively accelerated in throw 2. The results of the descriptive statistical analyses show a clear difference in the initial velocity between the 2 different throw executions: 109% in group 1, 87.2% in group 2, and 37.5% in group 3. The lowest value was 0.318 m·s21 in group 1, whereas the highest value was 2.8 m·s21 in group 2. The velocity variation of the initial movement is connected with a large variation of the other parameters. Thus, the value of Idecel in throw 2 concerning throw 1 increased by 86% in group 1, 70% in group 2, and 43% in group 3. The initial force shows a corresponding picture, with values of 96% in group 1, 59% in group 2, and 42% in group 3. The higher values of the deceleration of the initial movement and initial strength at all groups stands in connection with the increase in the parameters V50 (60% in group 1, 58% in group 2, and 60% in group 3) and I50 (70% in group 1, 40.5% in group 2, and 62.5% in group 3). Concerning the parameters Vend and Icph, throw 2 exhibited likewise higher values except in group 1, where the throw velocity and the impulse of the concentric phase were slightly under the values of throw 1. The differences in the parameters were checked with the paired t-test. The level of significance was initially set at p , 0.05. Because the present study included multiple comparisons involving the same subjects, a correction for the experimentwise error rate was required. Therefore, the alpha level was adjusted by the Bonferroni technique: a 5 0.05/8 5 0.00625. This level was then used to determine significance. The t-test values show that the differences of the average values of all variables differed significantly from each other. Similar values resulted when each group was examined separately. Here, the variables Vend and Icph, which in group 1 constitute the exception, statistically exhibited no significant differences. Concerning the same parameter, group 3 achieved significantly higher values

Vend (m·s21)

RESULTS

Group 1 Throw 1 Throw 2

Statistical analyses were carried out with SPSS 10.0 for Windows (SPSS Inc., Chicago, IL). Means and SDs were determined for each variable and condition. A paired Student’s t-test was used to determine any significant difference among the recorded parameters. Additionally, Pearson correlation coefficients were calculated among the parameters of the movement’s initial and concentric phases. Significance was accepted at p # 0.05.

4.87 6 1.68 8.28 6 3.11

Statistical Analyses

* Vinit 5 drawing-back speed; Iinit 5 impulse of the drawing-back phase; Idecel 5 deceleration impact; Fo 5 initial force; Vend 5 terminal velocity; V50 5 impulse of the concentric phase; I50 5 speed value during first 50 milliseconds of concentric phase; I cph 5 impulse value during first 50 milliseconds of concentric phase. † Vinit corresponded to individual feeling on throw 1 and was maximally negatively accelerated in throw 2.

Icph (nm)

tronic goniometer, which was placed at the rotation axis of the mobile part. The data of the goniometer were exclusively used for the estimation of each subject’s start position. The measuring data were analyzed with the software package Signalys (Ziegler, Moenchengladbach, Germany).

55 6 4.05 62.18 6 4.78

ET AL.

52.67 6 2.16 59.95 6 3.98

GREZIOS, GISSIS, SOTIROPOULOS

47.62 6 3.26 44.3 6 6.7

120

MUSCLE-CONTRACTION PROPERTIES IN OVERARM THROWING 121 TABLE 3. Correlation values among the determined variables of the measurement related to the entire population and attempt number.* Vinit Iinit Idecel Fo Vend V50 I50 Icph

Vinit

Iinit

Idecel

Fo

Vend

V50

I50

0.9615† 0.8891† 0.8880† 0.7570† 0.6777† 0.7570† 0.7376†

0.9118† 0.8976† 0.6685† 0.7950† 0.7867† 0.6352†

0.9682† 0.5114† 0.7013† 0.8276† 0.4791†

0.5315† 0.7416† 0.8778† 0.5072†

0.5473† 0.3919‡ 0.9768†

0.8434† 0.5669†

0.5669†

* Vinit 5 drawing-back speed; Iinit 5 impulse of the drawing-back phase; Idecel 5 deceleration impact; Fo 5 initial force; Vend 5 terminal velocity; V50 5 impulse of the concentric phase; I50 5 speed value during first 50 milliseconds of concentric phase; I cph 5 impulse value during first 50 milliseconds of concentric phase. † p , 0.001. ‡ p , 0.05.

than did group 2, though group 2 exhibited significantly higher values in the remaining parameters. The correlation-analytic results of the entire rehearsing and population of the measurements (Table 3) show a strong, positive relationship among the parameters Vinit and Iinit, Idecel, Fo, V50, and I50. This means that an increase of the initial movement speed is correlated with a higher deceleration impulse as well as a higher initial force level. These exert a strong influence on the first period (50 milliseconds) of the concentric phase, which the high correlation values imply. As already assumed from the descriptive statistic representation, the variables Vend and Icph exhibit middle correlation values. However, if one calculates the correlation between Vend and Idecel or Fo for only group 3, then one receives high correlation values of 0.7873 or 0.7801 (p , 0.001). This underscores the importance of initial strength of the overarm throw velocity as well, under the condition that the coordinative abilities of the athlete are well trained.

DISCUSSION The first hypothesis assumed the integral of the initial movement impulse would accordingly affect the level of the initial force as well as the throw velocity. As our results indicate, the deceleration impact, initial strength, and throw velocity values positively correlate such that the above hypothesis can be accepted. In this study, the impulse and speed parameters were also measured during the first 50 milliseconds of the concentric phase. Because voluntary muscle contractions are almost impossible in such a short period, the behavior of the parameter of this time indicates the influence of the stored elastic energy on the concentric contraction. As shown in our results, both the speed and the impulse of this period rose with an increase of the initial movement’s speed. More elastic energy was stored in the throw musculature because of the faster-accomplished initial movement. If one considers the mechanisms represented in the literature on jumps (3, 19), this energy can be accounted for by an increased recruiting of muscle fibers before the end of the initial movement. Both the preactivation and the reflex activities can be regarded as mechanisms accounting for an increased recruiting. Muscle preactivation is a firm component of a movement program (13, 31) whose function lies both in increased muscle stiffness and in increased sensitivity of

muscle spindle (8, 29). This is proven in many natural motions such as running, hopping, or jumping (14, 25, 29). It is obvious (7) this procedure also takes place in throwing, which likewise represents a natural movement. The observation that the duration and height of the preactivation increased by increasing the load (31) enables us to assume that by increasing the speed of the initial movement the preactivation level increases as well, particularly in those cases when the individual both ‘‘causes’’ and ‘‘receives’’ extension load. Minimum duration of the deceleration phase of 40–50 milliseconds would be necessary for a reflex activity (1, 4, 21, 23, 24, 31). In our study, the duration of the deceleration phase amounted to 212 milliseconds in throw 1 and 162 milliseconds in throw 2; therefore, from the temporal perspective a reflex activation is possible. Because of the method and the problem posed in this study, it cannot be said whether reflex potentials are caused during the execution of the free throw. According to reflex theory, however, we can assume reflex potentials are shown in throw 2 because of higher preactivation (higher sensitization of the muscle spindle) and higher stretch velocity than in throw 1. Concerning the neuromuscular control of eccentric muscle contractions, the CNS is believed to use unique control strategies (10). Although this view seems to be valid in the case of maximal eccentric contractions, the neuromuscular activity occurring in nearly maximal conditions of muscle stretch, and particularly in free athletic movements, still remains unclear. The second hypothesis assumed the execution of the self-selected throw would produce better results and that an increase of the extension load would cause inhibition reflexes. The present results do not confirm this assumption. The explanation for this is provided by the comparison of the values of the isometric maximum force with the initial strength. One would expect an inhibition if such extension loads, which could not be mastered by the voluntary force level of the throw musculature, were produced during the execution of the free throw. According to our results, this is not the case. The initial force values were so low compared with the isometric force that no inhibition of reflex activity can be expected. Before the second hypothesis is finally rejected or accepted, further research in the overarm throw movement must be conducted. During the test movement the inertia of the arm force–measuring apparatus was intercepted by nearly all muscles of the throw arm. In the case of the

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free throw, each segment of the kinematic chain is gradually more strongly loaded, so that at the end of the movement the weak lower-arm musculature has to master large loads, which can exceed the force potential of this group of muscles (30).

PRACTICAL APPLICATIONS Our study concludes that the SSC is the type of muscular contraction in the overarm throw and that the level of force developed before the concentric contraction determines the throw velocity. However, observing the initial movement in the various overarm throws, we realize important differences exist owing to environmental factors as well as tactical expediency. Thus, for example, the initial movement in baseball is performed downwards, upwards, and backwards (extensional form), whereas in water polo it is performed upwards and backwards. In team handball, the initial movement can also be executed in 2 ways depending on the thrower’s available time and received pressure. Because the initial extension movement is usually slow, the level of initial force developed during the transition from the initial to the main phase of the overarm throw cannot be considered important. The athlete should develop as high an acceleration of the joints of the kinematic chain as possible so that the inertia force that should overcome the next joint increases. In the short initial movement, the only way to achieve a high initial force is to increase the initial movement speed and with a transition into the main phase of the overarm throw as abruptly as possible. Depending on the execution of the throw, the initial movement has another function: In the first case it serves mainly a maximization of the acceleration distance, whereas in the second case it serves to produce extension forces. A trainer can locate the type of the throw that is required and improve the phase of the throw that affects the movendum speed. The throw speed improvement in the context of SSC should be performed via specific throw movements, with external loads, which do not disturb the dynamic and kinematic pattern.

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Address correspondence to Apostolos Grezios, agkrez@ pe.uth.gr.