Does counter-movement effect jump performance and does using the arms further this improvement when performing a vertical jump?

Introduction:

Vertical jumping contributes to performance in almost all sports, obviously some sports such as basketball use it a lot more that other sports such as tennis. When performing a motor task such as jumping, human beings typically start with countermovement (CM), CM can be described as a quick bend of the knees during which the body’s centre of mass drops before being propelled upwards (Harman et al, 1990). There is evidence to support that task performance is improved with CM, for instance, it has been shown that subjects achieve a greater jump height with CM than without. This is because subjects are able to produce more work and/or use the work more effectively in a countermovement jump (CMJ) than a non-CMJ (Bobbert et al, 1996).

Researchers to date have proposed different theories as to why CM has a positive effect on vertical jump performance. Enoka (1988) cited in Harman (1990) proposed the performance enhancing effects of the countermovement is that concentric contraction immediately following an eccentric stretch begins with the muscle already under considerable tension, making more chemical energy available for generation of force. A later study conducted by Harman et al (1990) proposed that CM use’s the stretch-shortening cycle in which eccentric muscle stretching stores elastic energy, which is in part released during immediate subsequent concentric muscle contraction. Hudson (1986) found a significant (P<0,05) relationship between the use of stored elastic energy and CMJ height. A recent study conducted by Bobbert et al (1996) supports this, they concluded that greater jump height in CMJ’s seemed to be due primarily to the fact that CMJ’s allow the subjects to attain greater joint momentum. Therefore more elastic energy can be produced during the CM, and individual muscles are able to produce more work after the CM. Several studies have concluded that CM can improve jump performance, these studies have concluded CM can improve jump height by as much as 12% (Enoka 1988; Harman 1990 and Bobbert et al 1996).

However when performing a CMJ the use of the arms is a very important factor that must be considered, vertical jumps are often characterised by swinging the arms.

Several studies have looked at arms and their effects on jump performance with variations in results. Harman et al, (1990) stated that the arms produced extra force for the propulsion of the body resulting in a 5% increase in performance. However much higher values were reported from Payne (1968) cited in Harman et al, (1990) who found a 12% increase in jump performance with arms compared to without and Luhtanen and Komi (1978) who found arms contributed a further 10% in performance.

Several theories have been concluded as to why the use of arms contribute to increased jump performance. Lees et al, (2004) stated increased velocity of take-off when performing a CMJ allowed the arms to build up energy early in the jump and transfer it to the rest of the body during the later stages of the jump. Bishop et al, (2004) found that maximal jump height was significantly larger in the ‘arm swing jumps’ compared to the ‘no arm swing jumps’ due to a higher height of the centre of mass and a larger vertical velocity of the centre of mass at takeoff. In the ‘arm swing jumps’, the arm motion resulted in the arms making a larger maximal contribution. Harman et al (1990) found both countermovement and arm swing both significantly (P<0.05) improved jump height. However, arm swing’s contribution was greater enhancing a peak total body centre of mass rise, both pre and post take-off. Countermovement only effected the post take-off rise.

The aims of this study are to determine whether CM has a positive effect on jump performance compared to that of no-CM and is this increased further by the use of arms. The writer believes that CM will have a positive effect on jump performance, and the arms will contribute to further in improvements in jump performance.

Method:

Two subjects, 1 male, aged 20 and 1 female aged 20 were taken from the practical class group (a), these subjects were required to perform 4 of each ...

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Method:

Two subjects, 1 male, aged 20 and 1 female aged 20 were taken from the practical class group (a), these subjects were required to perform 4 of each of the following performances:

A whole body vertical jump including counter-movement
A whole body vertical jump without counter-movement
A vertical jump using legs only with counter-movement
An upper body movement only, with straight legs

The subjects rest period between each jump was whilst the other subject was performing their jump. As far as possible, the body position including arm position, trunk inclination and depth of movement will be controlled through observation via two fellow students in the practical watching each jump performed. Timing of the events will be determined through use of a camera and video recorder.

The subjects’ will be required to complete a consent form and health questionnaire prior to testing (see appendix c.).

To avoid learning effects the testing will be randomised as follows:

Force data will be collected using a force platform and Bioware software. Timing data will be collected using video. The two systems will be synchronised using a timing light.

Results:

Table 1. Mean Data and SD (±)

Subject 1 (male):

Subject 2 (female):

Graphs of Mean Results

Subject 1 (mean results) Subject 2 (mean results)

Figure 1. Max flight height means for Subject 1 Figure 2. Max flight means for Subject 2

Figure 3. Take off Velocity means for Subject 1 Figure 4. Take off Velocity means for Subject 2

Figure 5. Vertical Impulse means for Subject 1 Figure 6. Vertical Impulse Means for Subject 2

Discussion:

The results collected for subject 1 was to be expected (see table 1); the subject-performed best in jump a, using CM and arms. This was hypothesised by the writer and supported by numerous researchers, research has concluded that jumping performance can be greatly improved with CM and arms compared to without (Bobbert et al, 1996; Enoka 1988; Harman et al, 1990; Payne 1968; Lees et al, 2004 and Bishop et al, 2004).

When comparing jump a (using CM and arms) to jump b (using no-CM) there is a 15% improvement in overall jumping performance in jump a (see table 1). This is supported by Bobbert et al (1996) who found CMJ’s produced greater jump heights than non-CMJ’s. This occurs as a result of greater vertical velocity CMJ’s produced a greater ground reaction force at the start of push off during the jump. Even though both jumps included the use of arms, research has found that effective jumping performance must include CM and arm swing simultaneously. Lees et al, (2004) concluded the arms caused an increase in energy when performing a CMJ, this energy came from the shoulder and elbow joints as well as from extra work done at the hip. The energy is used to (i) increase the kinetic and potential energy of the arms at take off (ii) store and release energy from the muscles and tendons around the ankle, knee and hip joint, and (iii) ‘pull’ on the body through an upward force acting on the trunk at the shoulder. Harman et al (1990) found that during countermovement, the use of arms results in less un-weighting, slower and less extensive total body centre of mass drop, and less negative power.

When comparing jump a (using CM and arms) and jump b (using no-CM) to jump c (using CM with legs only) there was a marked improvement in overall performance in jump a and b compared to that of jump c, with an improvement of 28% increase in jump height in jump a than that of jump c. The use of arm swing was prevalent in both jumps a and b and accounts for this improvement. Bishop et al, (2004) found that arm swing increases maximal jump height, this is due to both a higher centre of mass at take off and a larger vertical velocity of the centre of mass at take of.

The arm motion results in the arms making a larger maximal contribution to force during the middle of the propulsive phase and decreases the negative contribution of the trunk-head and thigh to force, late in the propulsive phase. Harman et al, (1990) found that arm swing results in higher peak vertical ground reaction force and peak positive power.

The results collected for subject 2 were not as expected (see table 1), the results did not correlate with previous research found, the data collected was scattered and there was no clear representation of a best jump. This could have occurred due to a number of factors, however the main factor that could have effected the reliability of the results is the estimation of subject 2 weight.

The recorded body weight of subject 2 was not recorded as accurately desired, therefore an estimate was required making the body mass indecisive. Body mass plays an important factor in the results of a vertical jump. Body mass is measured on a force plate. Owing to their high measuring accuracy, force plates have currently become well established for the determination of vertical jump height, however errors can be made. The force plate is sensitive to a correct body mass determination, therefore if more trials of the same subject are required when testing for maximal performance, a single body mass value should not be used for all of the trials (De Clercq et al, 2001). In this study however not only was one body mass used, but it was also incorrect, therefore an estimate had to be made, which could possibly account for the inaccuracy of results. This was not the case with subject 1 however, due to the fact that the subject’s weight was recorded properly.

However other factors could have also effected the subjects results. The subjects’ starting positions were observed and if looked correct were accounted for. Elvira et al, (2001) suggested that great care must be taken with protocols for performing numerous vertical jumps. Therefore human observation may have had an effect on the results due to human error.

The subjects’ results may have been effected by fatigue having performed a total of 16 jumps each. Bennett et al, (2000) stated that a decline in performance after fatigue may be the result of (i) a change in co-ordination, (ii) a change in functional capacity of the muscles to produce force, or (iii) a combination of these two factors.

However, Bennett et al, (2000) also found the execution of a vertical jump depends on the co-ordination of the segmental actions of the human body, which is determined by the interaction between the muscle forces. Therefore fatigue may have played a role in the discrepancies in performance for the subjects’ however, for subject 2 the results were inconclusive from the beginning, therefore eliminating fatigue as playing a major role in the inaccuracy of results.

Another factor that could have proposed inaccuracy, is the subjects’ level of training. Timing and co-ordination depends on the training of the subject. Training causes substantial saving of energy so that the movement becomes more correctly timed, with a reduction of overlapping activity within an agonist/antagonist pair and increase in

the ‘sharpness’ of activity of each involving muscle (Luhtanen and Komi 1978). The participants had not undergone any training prior to completing the study, which could account for the inaccuracy of results produced by subject 2.

Prior to completing the study, the participants were not given proper protocols to warm up, this may have subsided the subjects’ true performance potentials, Hunter and Marshall (2002) found that flexibility had a positive effect on jump performance. With the performers not properly warmed up the subjects’ flexibility would have been limited as a result.

Overall, subject 1 confirmed the writer’s hypothesis and met the aims of the study, providing evidence that CM increased vertical jump performance, and CM with the use of arms increased vertical jump performance further. Subject 2 did not confirm the writers hypothesis or meet the aims of the study, however, subject 2 has provided a learning curve for future study, providing evidence that recording data correctly and following strict protocols should remain essential when completing further testing. If the experiment were to be repeated ‘controls’ would have to be enforced to achieve more valid results. A sheet for recording personal details, such as height and weight should be included, reducing the risk of error when obtaining results. More observers could be used to determine whether jumps were performed correctly, and it not being validated till all of them were agreed.

References:

Bishop, E.J., Feltner, M.E., and Perez, C.M. (2004). Segmental and kinetic contributions in vertical jumps performed with and without an arm swing. Research Quarterly in Exercise Sport, 75, 216-30.

Bennett, S.J., Fowler, N.E., and Rodacki, A.L.F. (2000). Vertical jump co-ordination: fatigue effects. Medicine and Science in Sports and Exercise, 34, 105-116.

Bobbert, M.F., Gerritsen, K.G.M., Litjens, M.C.A., and Van Soest, A.J. (1996). Why is countermovement jump height greater than squat jump height? Medicine and Science in Sports and Exercise, 28, 1402-13.

De Clercq, D., Vanrenterghem, J., and Van Cleven, P. (2001). Necessary precautions in measuring correct vertical jumping height by means of force plate measurements. Ergonomics, 44, 814-818.

Elvira, J.L.L., Jodar, X.A., Riera, M.M., and Rodriguez, J.G. (2001). Comparative study of the reliability of three jump tests with two measurement systems. Journal of Human Movement Studies, 41, 369-383.

Enoka, R.M. (1988). Neuromechanical Basis of Kinesiology. Cited in Harman, E.A., Frykman, P.N., Rosenstein, M.T., and Rosenstein, R.M. (1990). The effects of arms and countermovement on vertical jumping. Medicine and Science in Sports and Exercise, 22, 825 – 833.

Harman, E.A., Frykman, P.N., Rosenstein, M.T., and Rosenstein, R.M. (1990). The effects of arms and countermovement on vertical jumping. Medicine and Science in Sports and Exercise, 22, 825 – 833.

Hudson, J.L. (1986). Co-ordination of segments in the vertical jump. Medicine and Science in Sports and Exercise, 18, 242-51.

Hunter, J.P., and Marshall, R.N. (2002). Effects of power and flexibility training on vertical jump technique. Medicine and Science in Sports and Exercise, 34, 478-86.

Lees, A., De Clercq, D., and Vanrenterghem, J. (2004). Understanding how an arm swing enhances performance in the vertical jump. Journal of Biomechanics, 37, 1929-40.

Luhtanen, P., and Komi, P.V. (1978). Segmental contribution to forces in vertical jump. European Journal of Applied Physiology, 38, 181-188.

Payne, A.H., Slater, W.J., and Telford, T. (1968). The use of force platform in the study of athletic activities. Cited in Harman, E.A., Frykman, P.N., Rosenstein, M.T., and Rosenstein, R.M. (1990). The effects of arms and countermovement on vertical jumping. Medicine and Science in Sports and Exercise, 22, 825 – 833.

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