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A Comparison of Two Landing Styles in a Two-Foot Vertical Jump

Gutiérrez-Davila, Marcos; Campos, José; Navarro, Enrique

Journal of Strength and Conditioning Research: January 2009 - Volume 23 - Issue 1 - p 325-331
doi: 10.1519/JSC.0b013e3181874806
Original Research
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Gutiérrez-Davila, M, Campos, J, and Navarro, E. A comparison of two landing styles in a two-foot vertical jump. J Strength Cond Res 23(1): 325-331, 2009-In team sports, such as basketball and volleyball, the players use different takeoff styles to make the vertical jump. The two-foot vertical jump styles have been classified according to the landing style and identified as hop style, when both feet touch the ground at the same time, and step-close style, when there is a slight delay between the first and second foot making contact with the ground. The aim of this research is to identify the differences between the two styles. Twenty-three subjects participated in the study, of whom 14 were volleyball players and 9 were basketball players. The jumps were video recorded and synchronized with two force platforms at 250 Hz. Two temporal periods of the takeoff were defined according to the reduction or increase in the radial distance between the center of gravity (CG) and the foot support (T - RDCG and T + RDCG, respectively). The findings produced no specific advantages when both styles were compared with respect to takeoff velocity and, consequently, to jump height, but takeoff time was significantly shorter (p < 0.001) in the hop style takeoff. However, this reduction was compensated for by the greater time employed in the last step of the approach run (p < 0.001). When the step-close style was used, the vertical velocity of CG at the beginning of the takeoff is significantly lower. Moreover, the mean vertical force developed during T − RDCG was reduced by −627.7 ± 251.1 N, thus lessening impact on landing. Horizontal velocity at the end of the takeoff is less when the step-close style is used (p < 0.005), suggesting that this style is better for jumps where it is necessary to move horizontally during the flight against an opponent.

1Department of Physical Education and Sport, University of Granada, Granada, Spain; 2Department of Physical Education and Sport, University of Valencia, Valencia, Spain; and 3Department of Physical Education and Sport, Polytechnic University of Madrid, Madrid, Spain

Address correspondence to Marcos Gutiérrez Dávila, marcosgd@ugr.es.

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Introduction

In sports where the vertical jump is especially relevant to performance-as is the case with basketball or volleyball-different takeoff styles are usually observed in the jump. Generally, these jumps are used when making certain important technical actions such as the shot at the basket in basketball or the shot or block in volleyball, which require not only an elevated jump but also the correct direction of forces to be able to overcome the opposition of the opposing player. These jumps are usually made with both feet after a two- or three-step run-up. These types of jumps vary according to the time that elapses between the contact of the feet with the ground during the landing phase before the takeoff for the jump. This fact enables us to differentiate two styles that have given rise to some controversy about their relative efficiency (5). Specifically, Coutts (6) identifies the styles as hop style, when both feet touch the ground at the same time, and step-close style, where the second, or trailing, foot takes longer to make contact with the ground. This paper aims to determine the differences between both styles using dynamometric and video recording techniques, and a methodology based on Dapena and Chung's (8) theoretical interpretation of the high jump takeoff.

The two-foot support vertical jump has been studied from a biomechanical viewpoint on many occasions and with different purposes: to evaluate different ways of muscle participation (3,15), to assess segmental participation (9,12,16), or to identify its determining efficiency factors (2,13,23). However, the jump generally is quantified on the basis of the vertical component of the force from a stationary position, with or without a countermovement, or on the basis of different heights, ignoring the effect on the takeoff phase produced by the run-up.

Takeoff analysis in vertical jumps with a run-up has focused on different goals: Dapena (7) and Dapena and Chung (8) have connected it to the high jump, Saunders (20) has assessed the effect of the run-up on takeoff effectiveness, and Vint and Hinrichs (22) have conducted a comparative study of one-foot and two-foot takeoffs. Dapena and Chung (8) found differences between radial and vertical motions in the takeoff phase of the vertical jump, underlining the need to use a theoretical model in takeoffs with a run-up different from that used in vertical jumps made from a standstill or with a countermovement. Following this model for the hop style, at the end of the approach run, the foot is placed in front of the center of gravity (CG), resisting the linear motion of the CG by flexing the takeoff leg. This action produces a radial distance (RDCG) reduction and the stretching of the muscles as the CG moves upward (Figure 1, B-C). The RDCG then increases, and the leg muscle in the takeoff leg shortens while the CG continues rising (Figure 1, C-E). The combined effect of fast horizontal velocity and the backward inclination of the body at the start of the takeoff facilitates reflex tension and other pretension mechanisms during the stretching of the muscles, which allows vertical force to increase as the muscles shorten (4,15).

Figure 1

Figure 1

On the basis of the vertical force recorded on a force platform and using a theoretical countermovement vertical jump model, Coutts (6) found significant differences between hop style and step-close style takeoffs. Among other divergences, he argues that, in the hop style, takeoff time is reduced and mean vertical force is significantly higher. These differences are caused by greater muscle pretension resulting from an increase in vertical velocity at the end of the run-up, as is the case with countermovement jumps from different heights (3,15). Despite the differences described by Coutts (6) between the two takeoff styles, no statistically significant differences have been found in vertical velocity at the end of the takeoff and, consequently, in the height of the jump.

Vint and Hinrichs (22), on comparing vertical jumps with one or two feet, took into account the values of the horizontal force component, adapting the methodology proposed by Dapena and Chung (8) for the two-foot vertical jump. In addition to recording the vertical displacement of CG, they analyzed the distance and radial velocity (RVCG) of CG, using the position of a vector that was defined from CG to the midpoint of both feet when they were firmly planted on the ground. Among other considerations in two-foot jumps, they found that when the minimum RDCG was reached, the vertical velocity of CG is positive, an important factor for performance of the vertical jump with a previous approach run. Coutts (6) did not assess this aspect when he compared takeoffs made in the hop style and step-close style. In his model of jump, he considered only the vertical displacement of CG based on the vertical force component and theoretically estimating the vertical position of CG at the start of the takeoff. In this way, when minimum height is reached, the vertical velocity of CG is always zero.

Our practical interest lies in discovering which of the two styles might have more advantages when making the jump in sports where there is opposition such as basketball and volleyball, and where, in addition to the height reached by the CG, the time required for its execution and the spatial orientation of the corporal segments are factors that determine the performance of the takeoff (18). Moreover, taking into account the high number of jumps made in these sports, a second practical aspect is the prevention of injuries based on the analysis of the values reached in the vertical and horizontal force components pushing against the ground when taking off for both landing styles.

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Methods

Experimental Approach to the Problem

This study was designed to check the effects of the two landing styles (hop style and step-close style) on the biomechanical factors that determine the efficiency of the takeoff in the two-foot vertical jump with a previous three-step approach run, and with arm movement. The styles are defined according to the delay in landing of the second foot with respect to the first. Hop style is defined as a takeoff where both feet make contact with the ground simultaneously. After analyzing the results, the criterion used to identify hop style was that the delay in the arrival of the second foot was less than 0.009 seconds. When both feet made contact with the ground at the same time, the first support was taken as being the foot that made the push-off on the last step of the approach run. Step-close style was defined as a takeoff where there was a time lag between the landing of the first foot and the second foot, the criterion to identify step-close style being a lag time of between 0.079 and 0.131 seconds.

The methodology proposed by Dapena and Chung (8) was adopted to evaluate the performance of the takeoff in the two-foot jumps. For the analysis of the radial movements (RDCG and RVCG), a position vector was defined from a rotation axis related to the support of the feet on the ground and the subject's CG. For the analysis of the vertical movements of the CG, the height of CG was recorded (YCG), as well as the vertical and horizontal velocity components of the time the takeoff took (YVCG and XVCG, respectively).

Bearing in mind the importance of the time taken in executing this action in sports where there is opposition such as basketball or volleyball, the flight time of the last step of the approach run (T flight-last step) and the time the takeoff lasts (T takeoff phase) were recorded for both landing styles. Takeoff time has been divided into two periods according to greater or lesser RDCG (T − RDCG and T + RDCG, respectively). The T − RDCG period is timed from the instant when the first takeoff foot touches the ground (T1) to the instant in which the minimum RDCG is achieved (T2), and T + RDCG is timed from T2 to the instant in which the second foot loses contact with the ground (T3).

Finally, this study seeks to check the effect produced by the delay of the second foot on the vertical and horizontal impulse components that each foot exerts in the T takeoff phase. For that, the percentage of total impulse exercised by the trailing foot against the ground during takeoff was measured (Y total delay foot [%] and X total delay foot [%], for the vertical and horizontal component, respectively). Because of the delay of the trailing foot, it is expected that in the step-close style, the second foot exerts less impulse against the ground during T − RDCG. According to Coutts' results (6) and the contributions of Andersen and Pandy (1) and Lees et al. (16), no differences should exist in the impulse components during T + RDCG. To test this hypothesis, the percentage of total impulse exercised by the trailing foot during T − RDCG was measured (Y − RDCG delay foot and X − RDCG delay foot, for the vertical and horizontal components, respectively) and that exercised during the time the RDCG is increasing (Y + RDCG delay foot and X + RDCG delay foot, for the vertical and horizontal components, respectively).

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Subjects

Twenty-three male physical education undergraduates participated in the study. Ten of them were recruited among university league basketball players, and the rest played university volleyball at national level (mean height: 179 ± 6.1 cm; mean mass: 70.96 ± 8.82 kg). At the time of this study, all of them were participating in competition. As a selection criterion, participants had to have command of both styles; this was checked by analyzing time consistency for 15 consecutive jumps using both styles, recording takeoff times and the delay of the second foot with respect to the first (21). The study from which these data were collected received local ethics committee approval, and all participants gave their written consent.

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Procedures

All the participants undertook a warm-up routine following the same protocol, doing general conditioning exercises to raise the body temperature as well as specific exercises for jumping. No stretching exercises were included because of their possible negative effect on the vertical jump (14,19). After the warm-up period and applying the same protocol to all subjects, each participant jumped five times in line with the conditions described for the hop style. After a 10-minute break, they jumped five more times in the step-close style. In both situations, the participants were asked to try to achieve the greatest height of jump possible. This order was alternated for each subject. From the five jumps recorded for each takeoff style, one was selected for subsequent analysis, taking into account the mean takeoff time. Because the XVCG of the approach run could influence takeoff, the participants were permitted to take three steps before starting the approach run, trying to reach the beginning of the takeoff phase at an XVCG sufficient to enable them to give the maximum performance in the vertical jump.

To quantify force components, two force platforms were used (Dinascan-IBV-Instituto Biomecánico de Valencia, Valencia, Spain), one for each foot at 250 Hz. The jumps were filmed with a high-speed video camera (Redlake Motion Space 1000 S) with the same frequency as the platforms. For the synchronization of the two platforms and the video camera, an electronic signal was used to activate the start (11). In each trial, the average horizontal and vertical force values from the two force platforms were calculated for a 0.08-second period after the subject lost contact with the platforms. These baseline values were then subtracted from all other force platform readings.

The velocity components and the positions adopted by the CG while the takeoff phase lasted were obtained by integrating the horizontal and vertical components of the force-time function obtained from trapezoidal integration of the horizontal and vertical components of the force-time function of the sum of the two platforms. The integration constants were drawn from images taken from the video camera. For a sequence of 10 images, among which was the contact of the first foot with the force platform, manual digitalization of the 21 points that make up the 14-segment mechanical model of each participant was used (16). Quinting spline functions (24) were then applied to the coordinates of each point. To prevent the introduction of possible systematic errors, the spline function was smoothed at zero value. For the calculation of the CG, position inertial parameters were used (segmental masses and center of mass locations) proposed by Zatsiorsky and Seluyanov (25) and adapted by de Leva (17). The position of the CG at the instant the first foot made contact on the force platform was considered the mean value of the CG positions of the two images among which contact was produced. For the computation of YVCG and XVCG, the same procedure was used on the basis of their respective derivatives corresponding to the times of the images among which contact occurred. For two-foot takeoffs, Vint and Hinrichs (22) locate the rotation axis at the midpoint of the horizontal coordinates of the heels and the tips of both feet when fully planted on the ground. This would certainly be a good method when both feet are together on the ground at the same level, but in our study it was observed that one foot was before the other, so using a fixed point as a rotation axis would cause an excessive error in the RDCG, especially at the beginning and at the end of the takeoff. Therefore, this research used as the rotation axis a point that shifts at constant velocity along the surface of the ground, from point A-determined by the mean horizontal coordinates of the center of both ankle joints and metatarsals of the first foot that lands, when this is firmly planted on the ground-and point B, which was determined by the mean horizontal coordinates of the midfoot (metatarsus) of both feet when fully planted on the ground (Figure 2). The average velocity of the rotation axis displacement along the contact surface was calculated using the quotient between the distance between points A and B and takeoff time. Once RDCG was determined for each position, RVCG was calculated by means of the derivative of the function with respect to time.

Figure 2

Figure 2

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Statistical Analyses

Data were statistically treated with the software Statgraphics 5.1 from Statistical Graphics Corporation (STCS, Inc., Rockville, Md). For each variable and experimental situation, the mean and standard deviation were calculated, and to quantify the differences between the variables of both takeoff styles, a repeated-measures (multifactorial) analysis of variance (ANOVA) was used.

To assess the reliability of tests, a simple ANOVA with repeated measures (five trials) was applied to both tests, taking as the dependent variable the support time of the jump. There were no significant differences between trials; the intraclass correlation coefficients were 0.977 (p < 0.001) for the step-close style jump and 0.988 (p < 0.001) for the hop style jump.

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Results

Table 1 presents the mean, standard deviation, and significance level of the T flight-last step and T takeoff phase for both landing styles. The T flight-last step value was significantly lower when the step-close style (p < 0.001) was used, whereas the T takeoff phase value was significantly lower with the hop style (p < 0.001). No differences were found when the T flight-last step and T takeoff phase values were added together. The time periods in which the takeoff was divided show that the T − RDCG value is significantly lower with the hop style (p < 0.001), whereas no statistically significant differences were found for T + RDCG. The data show that the T takeoff phase value is reduced in the hop style as a consequence of T − RDCG, whereas T + RDCG does not contribute to the reduction of takeoff time.

Table 1

Table 1

Table 2 presents the mean, standard deviation, and significance level of CG values for RDCG, RVCG, YCG, and YVCG of the CG for both landing styles. The data correspond to T1, T2, and T3. Mean RDCG values only show statistically significant differences (p < 0.001) at T1, its mean value being greater with the step-close style. No statistically significant differences were found, either for T2 or for T3. On the other hand, RVCG was greater in the hop style (p < 0.01), whereas no significant differences were found in T2 and T3.

Table 2

Table 2

The YCG value is similar in both styles for T1 and T3. The YCG mean values at T2 are slightly higher when the takeoff is performed in the step-close style (p < 0.05). The mean YVCG value at T1 is higher when the takeoff is performed in the hop style (p < 0.001), whereas no statistically significant differences are found in T2 and T3. The absence of significant differences at T3 indicates that the means of the height attained in the jump will be similar for both takeoff styles. Lastly, Table 2 sets out the mean, standard deviation, and significance level of the mean XVCG values for T1, T2, and T3. For this variable, some differences are found between the means (p < 0.05) only at T3, with values being higher when the hop style is used. These data demonstrate that in the step-close style takeoff, the reduction of XVCG is greater than in the hop style.

Table 3 presents the mean, standard deviation, and significance level of the horizontal and vertical components of impulse developed by the trailing foot in the takeoff for both landing styles, with the data expressed as percentages of the impulse components developed by both feet. The data demonstrate that in the hop style, the X total delay foot and Y total delay foot values are close to 50%, showing that both feet develop similar impulses. In step-close style, the impulse developed by the second, trailing foot is significantly reduced (p < 0.001) for both components.

Table 3

Table 3

The analysis of the phases into which the takeoff has been divided indicates that in the hop style, the mean values for X − RDCG delay foot and Y - RDCG delay foot are close to 50% (46.1 ± 11.1 and 48.0 ± 4.8, respectively). In the step-close style, the participation of the second, trailing foot is very significantly reduced (p < 0.001), behaving similarly to the way described for T takeoff phase. The X + RDCG delay foot and Y + RDCG delay foot values are close to 50% for both landing styles. The results demonstrate that during the T + RDCG period, the impulse is similar for both feet in both landing styles.

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Discussion

In accordance with these results, the mean time of the takeoff phase is shorter when the hop style is used, this being in line with Coutts' data (6). This reduction may well be beneficial in certain sports with an opponent and when performance time is a relevant effectiveness factor, as argued by Gutiérrez et al. (10) for the volleyball spike, and by Rojas et al. (18) for basketball jump shots. If the mean time values of the takeoff phase (Table 1) are considered, then only the period T - RDCG contributes to the takeoff time being shorter in the hop style. This fact will be conditioned by the active participation of both feet during the greater part of the T - RDCG period. In the step-close style, however, on average, just one foot is used for approximately 56% of the time this period lasts.

The temporal benefits shown in the hop style are reduced when T flight-last step is taken into account. The increase in flight time in the hop style is determined by the scissor movement of the legs that the player must make during the flight of the last step to arrive at takeoff with both feet simultaneously. This scissor movement of the legs during the last step causes the YVCG component at T1 to be significantly greater in the hop style (p < 0.001), as shown by the data in Table 2.

The results in Table 2 reveal no differences in YVCG at the end of the takeoff. Therefore, YCG values reached in both styles will be similar, thus confirming Coutts' results (6). He suggests there are no advantages in one style over the other with regard to YVCG at the end of the takeoff phase, although the step-close style would facilitate absorption of the impact force developed in the T − RDCG period or during muscular stretching, which could be favorable to prevent injuries. Indeed, our findings confirm Coutts' contributions and suggestions (6). Thus, in the step-close style, the time of the T - RDCG period increases by 0.05 ± 0.02 seconds, and the mean vertical force is reduced by −627.7 ± 251.1 N. However, no differences were found for the horizontal component. These data show that greater absorption of the vertical impulse occurs and that the strain exerted by the muscles in eccentric activity is reduced.

The findings are confirmed on verifying that, in the step-close style, RVCG at T1 (Table 3) is significantly lower (p < 0.01), and mean acceleration in the T − RDCG period drops by 4.11 ± 2.01 m·s−2. The vertical component alone is accountable for such differences (p < 0.001), with no differences being found in the horizontal component, possibly because the participants were allowed to take three run-up strides before starting the approach run in both takeoff styles, so that the final velocity at the end of the approach run was not too high.

The results indicate that, in the T − RDCG period, stretching velocity, reflex tension, and certain muscle pretension mechanisms are lower in the step-close style, and, consequently, the force applied in the T + RDCG period is reduced, especially that exerted by the trailing leg, as suggested by Asmussen and Bonde-Petersen (3) when comparing jumps from different heights and with no countermovement. Yet, the lack of significance of YVCG at the instance of takeoff (Table 3) does not confirm this reduction in vertical force during the T − RDCG period, this being in line with the findings of Coutts (6). However, he attributes this fact to the possible contribution of the horizontal force component. We failed to verify this in our study, and our data coincide with those of Andersen and Pandy (1). They argue that the use of the elastic energy built in during the period of muscular stretching or lengthening leads to local or segmental effectiveness in the following phase of muscular shortening, even though its effect on the jump's overall effectiveness or total performance has not been confirmed. This might be caused by the influence of segment participation on the tension exerted by the muscles in the vertical jump (16).

The theoretical model proposed by Dapena and Chung (8) for the high jump, in comparison with the countermovement jump, explains its effectiveness on the possibility of finishing the approach run (T1) with the CG behind the takeoff foot and a YVCG close to 0. This allows the CG to move upward as RDCG decreases, with T2 being reached with a relatively high positive YVCG (2.1 ± 0.1, for jumps > 2 m). Similarly, Vint and Hinrichs (22) confirm this advantage when comparing jumps performed with one and two feet. The results of our study show RDCG at T1 to be significantly greater when using the step-close style (p < 0.001), whereas YCG at the same instant is similar in both styles, confirming that the CG lags behind the first foot more when the step-close style is used, and that the YVCG will be lower at the beginning of the takeoff. These data indicate that there is a certain advantage in the step-close style in obtaining YVCG at T2. However, the results for this variable do not prove an advantage because no statistically significant differences were found, despite the higher means of the step-close style.

The absence of a higher increase in YVCG at T2 when using the step-close style could be attributable to smaller muscle pretension caused by the lower RVCG and YVCG at T1 (p < 0.01 and p < 0.001, respectively). This fact may cause the mean vertical force to decrease during the T + RDCG period (−627.7 ± 251.1 N) in comparison with that developed in the hop style and, especially, because of the slight participation of the second supporting leg (Table 3). This explanation is supported by differences found in YCG values at T2 (p < 0.05). Thus, the data show that in the step-close style, the vertical downward displacement of the CG is increased by 0.04 ± 0.03 m over hop style. In their analysis of the two-foot jump using a takeoff similar to that of the step-close style, Vint and Hinrichs (22) obtain slightly higher values than those from this study for YVCG at T2. This could be explained by the lower mean XVCG obtained by our sample at the end of the approach run. By increasing run-up velocity and using the step-close style, the advantage of this style over hop style might be confirmed, but this would require further research.

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Practical Applications

The height of the jump and the time taken in the execution of the technical skill considered as performance factors show no differences between the two styles. Therefore, the choice of one or another style of jump should not be done with the aim of achieving the highest jump but, rather, to jump differently to direct the forces and to adapt it better to the specific actions of the game. With the two-foot landing style (hop style), the time of executing the technical skill is reduced as a consequence of the reduction of takeoff time; this benefit disappears when T flight-last step is taken into account.

The results indicate that a step-close style landing may be the most appropriate for takeoffs with an approach run in sports with opponents such as volleyball or basketball. This suggestion for orienting practice is, in general, concerned only with takeoffs with an approach run and based on the considerations below.

The benefits given by this alternative step-close landing style are founded on the following aspects. First, there is a greater absorption of the vertical impulse, which may help to avoid injuries. With this situation, the lesser tension exercised by the musculature during the T − RDCG period and, particularly, of the trailing foot, does not bring about the anticipated reduction of force exerted against the ground during the T + RDCG period. Second, at higher approach velocities, the step-close style would have certain advantages over hop style, even though the YVCG at T2 is similar for both styles. Third, there is a greater reduction of the XVCG component in the step-close style. This aspect could be positive in jumps made near the net in volleyball or jump shots against an opponent in basketball, where excessive XVCG at the end of the takeoff could result in faults in the game.

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Keywords:

impulse; force platforms; video analysis

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