The relationship between jumping performance and ... - IOS Press

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Isokinetics and Exercise Science 10 (2002) 107–115 IOS Press

The relationship between jumping performance and isokinetic strength of hip and knee extensors and ankle plantar flexors Athanasios Tsiokanos a,∗, Eleftherios Kellisb , Athanasios Jamurtas a and Spiros Kellisc a

Department of Physical Education and Sport Sciences of Trikala, University of Thessaly, Greece Department of Physical Education and Sport Sciences of Serres, Aristotle University of Thessaloniki, Greece c Department of Physical Education and Sport Sciences of Thessaloniki, Aristotle University of Thessaloniki, Greece b

Abstract. The purpose of this study was to examine the relationship between vertical jumping performance and isokinetic moment of force of knee extensors, hip extensors and ankle plantar flexors in adult males. Twenty-nine males performed squat and counter movement jumps on an Egrojump device. The peak jumping height and the total work (height × body mass) were used as indicators of vertical jump performance. The subjects also performed three submaximal and three maximal isokinetic efforts of the hip extensors, knee extensors and ankle plantarflexors at angular velocities of 60, 120 and 180◦ ·s−1 on Cybex Norm Dynamometer. Pearson’s product correlation tests indicated that there was a significant (p < 0.05) positive relationship between vertical jumping height and total work with hip and knee extension moments, whereas low correlation coefficients between isokinetic moment of the ankle plantarflexors and jumping performance were found (p > 0.05). Multiple regression analysis indicated that linear combinations of isokinetic torques accounted for 38% and 42% of the countermovement and squat jumping height variance, respectively. In contrast, regression models using isokinetic torques could predict jumping work accounting for 75% (counter movement jump) and 69% (squat jump) of the variance. The above results indicate that there is a moderate to high relationship between isokinetic knee and hip extension torques and vertical jump performance parameters, especially when jumping height is multiplied by subject’s body weight. Furthermore, it appears that when using a linear combination of isokinetic torques from hip and knee joint muscle groups the multiple relationship between isokinetic tests and jumping performance is higher. Keywords: Vertical jump, isokinetic, knee, ankle, hip, prediction

1. Introduction Isokinetic dynamometers are extensively used to evaluate muscular strength of lower leg muscles, in the form of maximal torque output exerted by isolated muscle groups around the hip, the knee and ankle joints at various angular velocities. The objective assessment of muscle function using isokinetic measurements allows the production of comparable and reproducible results. ∗ Address for correspondence: Dr. Athanasios Tsiokanos, Pilaias 85, 544 54, Thessaloniki, Greece. Fax: +30 4310 47042; E-mail: [email protected].

ISSN 0959-3020/01/$8.00  2002 – IOS Press. All rights reserved

For this purpose, isokinetic dynamometers are popular and easily applicable for maximal strength assessment. An important issue in the use of isokinetic dynamometers is the relationship between isokinetic torque measurements and functional performance. Several studies [2,7,17,19] have examined this issue and especially the relationship between isokinetic torque and vertical jumping performance [5,12,18,20– 22]. However, most studies [5,12,18,21,22] examined the relationship only between knee extensor torque and vertical jumping height with conflicting findings. For example, Destaso et al. [7] found high correlation coefficients between isokinetic eccentric and concentric torques and drop jumping performance and suggested

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that isokinetic measurements are useful for guiding the training and rehabilitation process. In contrast, Blackburn and Morrisey [1] reported a very low relationship between knee extensor strength (open kinetic chain exercise) and vertical jump performance. In contrast, the relationship between squat exercise (closed kinetic chain exercise) and vertical jump performance was high. It was suggested [1] that one of the reasons for the above results, is that the open kinetic chain test involved only the exerted strength of the knee extensor muscle group. The examination of the relationship between maximum strength of hip, knee and ankle muscles with vertical jump performance was recommended [1]. The vertical jump test is used as a laboratory or field functional test to measure power output of the legs. It is considered to be a component of performance because of its involvement in the activities of various explosive sports (track and field events, volleyball, weight lifting). Since vertical jumping is a multijoint activity which involves the simultaneous activity of various muscles, the examination of the relationship between muscle strength of muscles across the hip, knee and ankle and vertical jump performance is worthwhile. A possible close relationship between multiple isokinetic strength measures around more than one joints and vertical jump performance would indicate that the functional importance of isokinetic strength measurements requires multiple joint testing rather than single joint measurements. Consequently, the purpose of the present study was to determine the relationship between vertical jumping performance and isokinetic torque of knee extensors, hip extensors and ankle plantar flexors. 2. Methods 2.1. Subjects Twenty-nine male students of physical education volunteered to participate in this study. Their mean (± SD) age, height, and weight were 22.1 (± 2.2) years, 178.8 (± 6.3) cm and 77.2 (± 8.7) kg respectively. Before participating in the study, the subjects read and signed a consent form. 2.2. Testing The testing was conducting over two days. Vertical jumps were performed at the first day and isokinetic testing was evaluated at the second day. In each testing session, all subjects performed a 15-min warm-up on a stationary cycle ergometer, followed by stretching exercises of the leg muscle groups.

2.2.1. Vertical jumps All jumps were performed on the “Ergojump” platform [4]. Each subject performed three maximal voluntary vertical jumps at each of two testing conditions – Squat Jump (SJ) and Counter-Movement Jump (CMJ). The SJ was performed from a starting position with the subjects’ knees flexed to 90ª, with the hands fixed on the hips throughout, and with no allowance for preparatory counter-movement. The CMJ was performed from an upright standing position, with the hands fixed on the hips throughout, and with a counter-movement preparatory phase ended at a position corresponded to the starting position in SJ. The rise of CG above the ground for each jump was calculated from the flight time as proposed by Bosco et al. [4]. Sufficient recovery time was allowed among trials and the best of the three trials for each jump condition was recorded for further analysis. For the squat and counter movement jumps, two parameters were estimated: first, the maximum jumping height (the rise of CG above the ground) and second, the product of height and subject’s body weight, which is an indicator of the total work produced by the total body in each jump, as implemented by Genuario and Dolgener [12]. The latter parameter will be referred to as “total work” in the remaining of the article. 2.2.2. Isokinetic testing A Cybex Norm (Lumex Corporation, Ronkohoma, NY) isokinetic dynamometer was used to measure the torque developed during isokinetic hip extension, knee extension, and ankle plantar flexion. Particularly, hip extension was performed with the subjects at supine position. The knee was allowed to flex passively as a result of gravity whereas a stabilizing strap was placed around the waist. The resistance thigh pad was placed just proximal to the knee. Alignment of the joint and dynamometer axes of rotation was achieved by placing the axis of the actuator against the greater trochanter. The hip extension motion was performed through a range of 90 ◦ , with the starting position at 90◦ flexion, and the ending position at 0o (neutral horizontal position). Knee extension was performed with the subjects in the seated position, with their hands gripping the sides of the dynamometer chair. Stabilizing straps were placed around the thorax, pelvis and the thigh. The resistance shin pad was placed at a level just above the medial malleolus. The subjects were positioned so that the axis of rotation of the lever arm of the device coincided with the line passing transversely through the


femoral condyles. The range of motion for the knee was from 90◦ to 0◦ (full extension). Ankle plantar flexion was performed with the subjects at prone position and the knee in full extension (0◦ ). Stabilizing straps were placed around the ankle, shank and thigh. The range of movement was 55 ◦ , from 15 ◦ dorsiflexion to 40 ◦ plantar flexion. For each test, three submaximal efforts at angular velocities of 60 ◦ ·s−1 , 120◦ ·s−1 and 180 ◦ ·s−1 were performed for familiarization and warm-up purposes. The subjects then performed three maximal concentric efforts at 60◦ ·s−1 , 120◦·s−1 and 180 ◦·s−1 . A 30 sec time interval was provided between repetitions whereas a five minutes rest period was given between angular velocity tests. The sequence of tests was randomized across joints and testing velocities. Gravity correction was performed for the three joint tests according to manufacturers’ instructions. The maximum isokinetic torque produced at each testing condition for each joint test was recorded and used for further analysis. The peak torque values were normalized for body weight in order to be able to compare our results with previous findings.

3. Statistical analysis Pearson Product Moment Correlation analyses were conducted to determine the relationship between isokinetic strength (nine peak torque parameters) and jumping (SJ and CMJ) parameters. The significance level was at p < 0.05. Multiple regression analysis was applied to examine the relationship between combinations of peak torque values and jumping parameters (height and total work). An important issue when applying multiple regression techniques is that of multicollinearity. This takes place when the predictor variables are highly intercorrelated. In the present study, there were 9 predictor variables (three torque values for each joint tested). In order to avoid collinearity we applied regression equations using all possible combinations of the predictor variables to explain the variance of the dependent variable. From these, three linear models that explained the largest proportion of variance of the predicted variable while producing stable regression coefficients were selected. The stability of the regression coefficients was ensured by either high tolerance values or alternately low values of the variance inflation factor of each of the incorporated independent variables.

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4. Results The mean and standard deviation for the countermovement, squat jump and isokinetic torque variables are presented in Table 1. 4.1. Correlation coefficients The correlation coefficients among measured variables are presented in Table 2. For the squat jumps, it appears that the jumping height had a moderate relationship with the hip and knee torques at 180 ◦ ·s−1 (Fig. 1(a)). The correlation coefficients between the squat jump work and the isokinetic parameters were higher, with the highest being observed between with knee extension torque at 120 ◦ ·s−1 (Fig. 1(b), Table 2). For the counter movement jumps, it appears that the jumping height demonstrated low to moderate correlation coefficients with all isokinetic measures with the hip and knee torques at 180 ◦ ·s−1 (Fig. 2(a)) demonstrating the highest coefficients (Table 2). The correlation coefficients between the counter movement jump work and the isokinetic parameters were high, with the highest coefficient observed with the knee extension torques at 120 ◦·s−1 (Fig. 2(b)) and 180 ◦·s−1 (Table 2). 4.2. Regression equations The regression prediction equations are presented in Table 3. The countermovement jump height (CMJh) was predicted using linear combinations of knee extension torque at 180 ◦ ·s−1 , the hip extension torque at 180◦ ·s−1 and ankle torque at 120 ◦ ·s−1 , accounting for the 38% of the variance of the CMJh (R 2 = 0.38, F (3, 25) = 5.21, p < 0.05). The countermovement jump work (CMJw) was predicted using a linear combination of the knee torque at 120 ◦ ·s−1 , the hip torque at 180 ◦ ·s−1 and ankle torque at 60 ◦ ·s−1 (Eq. (2), Table 3) and accounted for 75% of the variance of the CMJw (R2 = 0.75, F (3, 25) = 24.90, p < 0.05). The multiple relationship between the squat jump height (SJh) and linear combinations of torque variables was described using the knee and ankle torques at 120◦·s−1 and the hip torque at 180 ◦ ·s−1 . The resulting equation (Eq. (3), Table 3) accounted for 42% of the variance of the SJh (R 2 = 0.42, F (3, 25) = 5.94, p < 0.05). The squat jump work (SJw) was expressed using linear combination of the knee torque at 120 ◦ ·s−1 , the hip torque at 180 ◦ ·s−1 and the ankle torque at 120 ◦ ·s−1 (Eq. (4), Table 3) accounting for 69% of the variance of the SJw (R2 = 0.69, F (3, 25) = 18.37, p < 0.05).

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A. Tsiokanos et al. / The relationship between jumping performance and isokinetic strength Table 1 Means and standard deviations of jumping and isokinetic variables Variables

SJh (cm) CMJh (cm) SJw (kp-m) CMJw (kp-m) H60 (Nm) H120 (Nm) H180 (Nm) K60 (Nm) K120 (Nm) K180 (Nm) A60 (Nm) A120 (Nm) A180 (Nm)

Non-normalized values Mean SD 31.5 3.6 35.5 4.1 24.43 4.38 27.50 4.70 265.55 45.45 252.90 44.85 234.21 56.12 220.69 32.10 189.31 27.91 145.86 23.77 86.17 18.31 64.45 15.62 48.86 12.84

Normalized values∗ Mean SD – – – – 3.46 3.27 3.03 2.86 2.45 1.89 1.13 0.84 0.64

– – – – 0.58 0.45 0.61 0.29 0.24 0.23 0.25 0.21 0.18

∗ Values

of isokinetic variables divided by body weight. (SJh = squat jumping height; SJw = squat jump total work; CJh = Countermovement Jumping Height; CMJw = Countermovement jump work; H60 – Hip extension torque at 60◦ ·s−1 ; H120 – Hip extension torque at 120◦ ·s−1 ; H180 – Hip extension torque at 180◦ ·s−1 ; K60 – Knee extension torque at 60◦ ·s−1 ; K120 – Knee extension torque at 120◦ ·s−1 ; K180 – Knee extension torque at 180◦ ·s−1 ; A60 – Ankle plantarflexion torque at 60◦ ·s−1 ; A120 – Ankle plantarflexion torque at 120◦ ·s−1 ; A180 – Ankle plantarflexion torque at 180◦ ·s−1 ).

Table 2 Pearson moment correlation coefficients between different variables 2 SJh (cm) 0.850∗∗ CMJh (cm) – SJw (kp-m) – CMJw (kp-m) – H60 (Nm) – H120 (Nm) – H180 (Nm) – K60 (Nm) – K120 (Nm) – K180 (Nm) – A60 (Nm) – A120 (Nm) – A180 (Nm) –

3 0.821∗∗ 0.657∗∗ – – – – – – – – – – –

4 0.765∗∗ 0.783∗∗ 0.943∗∗ – – – – – – – – – –

5 0.270 0.232 0.369∗ 0.369∗ – – – – – – – – –

6 0.390∗ 0.389∗ 0.622∗∗ 0.659∗∗ 0.853∗∗ – – – – – – – –

7 0.538∗∗ 0.522∗∗ 0.648∗∗ 0.671∗∗ 0.729∗∗ 0.828∗∗ – – – – – – –

8 0.490∗∗ 0.465∗ 0.739∗ ∗ 0.756∗ ∗ 0.617∗ ∗ 0.761∗ ∗ 0.641∗ ∗ – – – – – –

9 0.572∗∗ 0.570∗∗ 0.810∗∗ 0.848∗∗ 0.486∗∗ 0.717∗∗ 0.632∗∗ 0.912∗∗ – – – – –

10 0.589∗∗ 0.642∗∗ 0.778∗∗ 0.847∗∗ 0.444∗ 0.653∗∗ 0.681∗∗ 0.802∗∗ 0.913∗∗ – – – –

11 0.459∗ 0.368∗ 0.375∗ 0.333 0.567∗ ∗ 0.496∗ ∗ 0.517∗ ∗ 0.333 0.300 0.396∗ – – –

12 0.396∗ 0.329 0.314 0.285 0.548∗∗ 0.486∗∗ 0.349 0.341 0.297 0.352 0.803∗∗ – –

13 0.347 0.305 277 258 0.450∗ 0.422∗ 0.353 0.352 0.306 0.367 0.610∗∗ 0.837∗∗ –

∗ = Significant at a = 0.05, ∗∗ = significant at a =0.01. (SJh = squat jumping height; SJw = squat jump total work; CJh = Countermovement Jumping Height; CMJw = Countermovement jump work; H60 – Hip extension torque at 60◦ ·s−1 ; H120 – Hip extension torque at 120◦ ·s−1 ; H180 – Hip extension torque at 180◦ ·s−1 ; K60 – Knee extension torque at 60◦ ·s−1 ; K120 – Knee extension torque at 120◦ ·s−1 ; K180 – Knee extension torque at 180◦ ·s−1 ; A60 – Ankle plantarflexion torque at 60◦ ·s−1 ; A120 – Ankle plantarflexion torque at 120◦ ·s−1 ; A180 – Ankle plantarflexion torque at 180◦ ·s−1 ).

5. Discussion The main finding of the present study is that there is a moderate to strong relationship between isokinetic torques around the knee, ankle and hip and vertical jump performance parameters. The regression analysis indicated a high multiple relationship between vertical jump performance work and linear combinations of two

or more isokinetic torque parameters across different joints and angular velocities. The present results indicated a significant positive relationship between jumping variables (height, total work) and isokinetic knee extension and hip extension torques (Table 2) which is in agreement with some studies [5,18] and in contrast to others [12]. For example, Bosco et al. [5] found correlation coefficients


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(a)

(b)

Fig. 1. Relationship between squat jump height (a) and total work (b) and knee extension torque.

of 0.51 and 0.64 between SJh and isokinetic knee extension torque at 120 ◦ ·s−1 and 180 ◦·s−1 , respectively. The corresponding coefficients for CMJh and isokinetic torques at the same angular velocities were 0.65 and 0.64, respectively. These values are in agreement with the present results. In contrast, the correlation coef-

ficients between the isokinetic torque at 180 ◦·s−1 and jumping performance in our study are higher than those reported by Genuario and Dolgener [12] and Blackburn and Morrisey [1]. Furthermore, in the present study, the peak torque of the ankle plantarflexors, especially at moderate and fast angular velocities demonstrated

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(a)

(b)

Fig. 2. Relationship between countermovement jump height (a) and total work (b) and knee extension torque.

low correlation coefficients with jumping height and total work. This is in agreement with the results by Genuario and Dolgener [12], who reported correlation coefficients between vertical jump and plantarflexion torques ranging from 0.17 to 0.42. These results sup-

port a rather minor functional importance of isokinetic ankle strength tests for vertical jumping performance. The relationship between isokinetic strength and vertical jump performance increased when total work (SJw, CMJw) was used as an indicator of jumping per-


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Table 3 Regression equations on the relationship between peak torques and jumping performance variables Predicted variable CMJh CMw SJh SJw

Regression equation YCMJh = 0.056 × K120 + 0.017 × H180 + 0.035 × A120 + 18.825 YCMJw = 0.119 × K120 + 0.018 × H180 + 0.019 × A60 + 0.506 YSJh = 0.046 × K120 + 0.015 × H180 + 0.047 × A120 + 16.172 YSJw = 0.104 × K120 + 0.017 × H180 + 0.012 × A120 + 0.071

Equation No 1 2 3 4

(SJh = squat jumping height; SJw = squat jump total work; CJh = Countermovement Jumping Height; CMJw = Countermovement jump work; H180 – Hip extension torque at 180◦ ·s−1 ; K120 – Knee extension torque at 120◦ ·s−1 ; K180 – Knee extension torque at 180◦ ·s−1 ; A60 – Ankle plantarflexion torque at 60◦ ·s−1 ; A120 – Ankle plantarflexion torque at 120◦ ·s−1 ).

formance. This is in agreement with the results by Genuario and Dolgener [12]. It appears, therefore, that when the subject’s body weight is incorporated into computation of total work, this leads to a more representative indicator of the subject’s jumping abilities. Assuming that two subjects jump the same height, the heavier of the two will have a greater jumping ability, because he/she has to overcome a higher external resistance (gravity) during jumping. This is reflected when the total work is used as a jump performance indicator. The multiple regression results indicated relatively low multiple relationship between jumping height and linear combinations of hip, knee and ankle torques but with relatively low to moderate regression coefficients (from 35% to 42%). These values are however much higher than those reported by Destaso et al. [7] who found that maximal peak torque measurements could account for 23% of the variance of the vertical jump height. On the basis of these results, these authors suggested that the stretch-shortening cycle movements can be simulated using isokinetic strength tests. However, it is our opinion, the regression coefficients reported both by Destaso et al. [7] and in our study do not provide full justification that isokinetic strength tests can simulate vertical jump performance. In any case, our results indicate that when examining the functional use of isokinetic strength tests, the use of multiple isokinetic tests of the joints which participate in the movement in question may be more important compared to the use of single joint tests. An interesting finding of the present study was that when the jumping height was multiplied by the subjects’ body weight, the result (total work) either in squat jump or countermovement jump was explained by combinations of isokinetic torques with much higher (compared to jumping height) regression coefficients, ranging from 65% to 75%. These values are much higher than those previously reported on the relationship between isokinetic variables and functional performance [1,7,12] thus providing a new interesting di-

mension into this issue. As already have been mentioned, this reflects the highest correlation between total work and isokinetic torques. It also indicates that jumping work could be used as an indicator of jumping performance, when attempting to relate jumping tests to maximal strength tests. The regression analysis indicated that when attempting to relate isokinetic strength to jumping performance, isokinetic tests should include a variety of angular velocities across all joints of the lower extremity. It should, however, be mentioned that among the 9 torque variables which were measured, only one of the resulting regression equations included isokinetic torques at 60 ◦ ·s−1 . This is in agreement with previous studies [5,12,18,21] and indicates that isokinetic strength tests at slow angular velocities may not provide useful information to strength coaches on the relationship between maximal strength and jumping abilities of their athletes. The moderate to high correlation and regression coefficients indicate that there is a close relationship between isokinetic knee and hip torques and vertical jumps. The low regression coefficients in some cases reflect the differences in musculoskeletal function between the two movements. Isokinetics are open kinetic chain tests, which involve the evaluation of an isolated active muscle group through one leg movement with restrictions of the joint angular velocity. In contrast, vertical jumps are closed kinetic chain tests where various muscle groups of both legs are activated, whilst there is transfer of energy between segments, with acceleration and deceleration phases in the movement. The above should always be considered when examining the relationship in performance using the two aforementioned tests. However, this does not preclude the examination of the functional importance of isokinetics because isokinetic strength tests are the only tests which can provide objective and safe assessment of muscle strength under in vivo conditions and for this reason, they are applied to monitor training progress

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of athletes or the effectiveness of various rehabilitation programmes. The regression equations developed in the present study could also be used to predict vertical jump performance from isokinetic strength testing. This could be useful at the early stages of the rehabilitation process, where the performance of vertical jump tests is impossible. The predictive ability of the present models appears stronger than previously published equations [5,21]. This indicates that the equations might be useful to predict jumping performance in highly active males with an acceptable accuracy. However, further research is required to examine the validity of the above equations using cross-validation analysis in a different sample. Once the validation procedure is successfully completed, the equations could be used by clinicians to predict jump performance, when necessary. The database relating to isokinetic values of hip muscles is particularly poor. The subjects in our study exhibit higher peak torque values than those reported by others [2,6]. The subjects’ training level and the age parameter probably was responsible for the differences. A number of investigations are related to isokinetic ankle plantarflexion characteristics [9–11,14–16]. Our results are also similar to the findings reported by Fugl-Meyer et al. [11] and Fugl-Meyer [9] using the same testing angular velocities. Finally, our normative values for knee extension torque are in agreement with previous results [3,8,13]. For example, Highgenboten et al. [13] presented normalized (Nm/BW) knee extensor strength values (2.98 at 50 ◦ ·s−1 ) for 15–24 years old subjects, which are in agreement to our findings (2.86 at 60 ◦ ·s−1 ). In conclusion, the results of the present study a significant moderate to high relationship between isokinetic strength assessment of the knee and the hip extensor muscle groups and vertical jump performance, especially at slow and fast angular velocities. It appears that the relationship between isokinetic strength tests and functional performance should take into consideration maximum strength measurements collected from various muscle groups which play a major role for the performance of the functional movement under examination.

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