The aim of this study was to investigate the effect of external wrist weights on maximal countermovement vertical jump height. Data was collected from a group of eight Loughborough University students, who each performed three sets of jumps on a Kistler Quattro Jump platform with a variety of wrist weights. Though there were individual differences between subjects in the results, generally higher jumps were achieved when using external wrist weights, leading us to the conclusion that external weights on the wrists enhance performance, even if this is not the case when weights are attached to different body landmarks.
Vertical jumping is a simple plyometric activity common to many different sports and tasks such as vertical jumps, hops, and/or bounding movements are often used to increase explosiveness and strength of the lower extremities (Ebben, 2005). Plyometric exercise uses the stretch-shorten cycle to train muscles to do more work in less time. In plyometric activities, muscles rapidly switch from an eccentric action to a concentric contraction, essentially leaving no time for the muscle to relax. Stored elastic energy in the muscle and the stretch reflex summate to permit the muscle to create greater force (McNeely, 2005). Experimental studies have investigated the anthropometric factors affecting vertical jump height (Wyon et al, 2007), the kinematics and kinetics of jumping (Schenau, 1985) and the effects of neuromuscular training on vertical jump height (Gerritsen, 2000). Computer simulation models have also been used to further investigate jumping, for example the effect of initial jumping posture on maximal vertical jump height (Selbie, 1996).
This study investigates the effect of external weight on maximal countermovement vertical jump height. There is currently little knowledge in this area however there has been one study to date, investigating work and power production in the vertical jump under various loads fixed to the upper body or ankles (C. Corwin, 1998). A weighted vest was utilized to increase upper body mass in steps from 0 to 50 lbs in five skilled male jumpers. The subjects then performed a series of maximum effort non-countermovement jumps from a standardized starting position. After the weighted vest trials, ankle weights were used to increase the mass of the lower body.
The study reported that jump heights decreased as the load on the body increased for both vest and ankle weight conditions. The usefulness of the study is limited, since it was applied to only five, skilled subjects, and only tested two body sites. Therefore the external validity is low, as we have no evidence that the conclusions can be applied to the healthy population. We can also question the internal validity, since there are only five subjects; it is difficult to say whether the relationship between the weights and jump height was a causal relationship. The aim of this study is to add to our understanding in this area, by investigating the effect of wrist weights on maximal countermovement vertical jump height. The results from Corwin’s investigation lead us to hypothesize that increasing wrist weights will reduce maximal countermovement vertical jump height.
Eight Loughborough University students, (height 1.795 + 0.095m, mass 71.2 + 16.8kg) performed a series of countermovement vertical jumps with maximal voluntary effort on a Kistler Quattro Jump platform. Each subject performed three sets of three individual jumps, and was exposed to all treatment levels, i.e. no wrist weights (baseline measurement), 1.5kg attached to wrists (0.75kg each) and 3kg (1.5kg each) attached to each wrist. To minimise the impact on the experiment of order effects, counterbalancing was used to randomise the order of treatments. Though the subjects were obviously aware when they were jumping with no external weights, they were not otherwise informed which wrist weights (1.5 or 3kg) they were jumping with.
Before the experiment, each member of the group was weighed and their height recorded. The subjects were then instructed to sit in an isolated waiting area away from the testing environment, and asked not to discuss the experiment. Each member of the group was called individually into the testing area, where they were briefed on the task and performed a practice jump.
The subject then performed three maximal countermovement vertical jumps under each treatment level as stated, to be recorded using Kistler Quattro Jump software. The subjects were given verbal encouragement by the group to try to attain maximum height in each jump. On completion of three successfully recorded jumps, the subjects returned to the waiting area and the next subject was called in for testing. This process was repeated until each subject had been tested on three separate occasions, giving a total of nine recorded jumps per subject. The subjects were then asked to complete a performance related questionnaire.
A digital video camera was set up to record each individual jump in front of the Kistler Quattro Jump platform, and face on footage of each trial was recorded. This was a precautionary step taken in case the Kistler Quattro Jump software failed or was not successfully implemented, providing an alternative method to calculate vertical jump height.
For the purpose of this section data for one of the eight subjects was excluded. This is because in the questionnaire, they answered the question: ‘Do you think you input a consistent effort into each jump?’ by saying ‘no’. Since the purpose of the test was to measure maximal countermovement jump height, the data was discarded. All other subjects answered ‘yes’ or ‘varied slightly’ which were considered acceptable responses for our purposes.
Generally the uses of external weights attached to the wrists increased jump height (Table 1), with subjects mean jump height statistically significantly higher with the 3kg weights than none at all, as shown by a dependent samples t-test t(7) = 3.75,p ; .005. The 3kg condition tended to produce the highest jumps but the same test showed that there was no statistical difference between the 0kg and 1.5kg conditions t(7)=1.09,p;.005.
No addition weights
There were individual differences between subjects jump height and the influence of external weights (Figure 1). Using 1.5kg additional mass, the jumping height varies between -2.7% and +4.1% of the baseline measure (no external weights). Using 3kg additional mass, the jumping height varies between +0.2% and +9.2% of the baseline. The mean percentage increase between 0kg and 3kg conditions was 5.1%.
Previous studies showing that additional weights applied to the upper body and ankles decrease jump height, led to the hypothesis for this experiment, that increasing wrist weights will also reduce maximal countermovement vertical jump height. However the results show that the opposite was true for the sample considered, with subjects jumping on average 5.1% higher when using 3kg weights as a pose to none at all.
In relation to Corwin’s study, the results are of stark contrast, possibly suggesting that the location of external weights on the body may have a more significant effect on jump height, than the size of the weight itself. The graphs below show how jump height decreases with greater ankle and wrist weights, but increases with the use of wrist weights.
Considering Newton’s second law of motion (G.Hay, 1978), and the way the arms propel the body upwards in a countermovement vertical jump, it is possible that the additional mass on the wrists increased momentum in the upward phase of the jump, in turn leading to the increase in jump height which was evident. Whereas upper body and ankle weights would simply serve to ‘weigh the subject down’, and inhibit jumping ability. The difference in results may also have been affected by several other influences as discussed in the introduction. For example, previous studies have shown that jump height can also be influenced by anthropometric factors (Wyon et al, 2007), neuromuscular training (Gerritsen, 2000) and initial jumping posture (Selbie, 1996).
It is possible that the results may have been influenced by some shortcomings of the methodology. Due to the nature of the experiment, it was impossible to conduct the tests under blind or double blind conditions. Though the subject was not made aware of the quantity of external weights, they were obviously aware whether the weights were present or not. Similarly it was necessary for certain group members to be conscious of the various experimental conditions to successfully record the data.
This means that the data was susceptible to some extent, to the knowledge of the subject and the experimenters. For example, the experimenters may have been focused on ensuring some sort of correlation during the experiment, rather than remaining open minded. To encourage such trends, levels of motivation given to subjects may not have been consistent throughout, and could have introduced a degree of bias in the data collection process. Using a blind or double blind approach would help to minimise error, self deception and bias, thereby increasing the validity of the results.
The sample of subjects consisted of eight Sports Technology students from Loughborough University (height 1.795 + 0.095m, mass 71.2 + 16.8kg). The subjects were of similar age groups and would all be considered to be relatively fit. Therefore it is questionable as to how these results can be applied to larger populations. Ideally, we would have had a much larger number of subjects selected using a completely random method from a more diverse population, to make the results more externally valid. Therefore it is difficult to apply these results to different populations, for example thirty year old office workers.
Though it was possible to limit learning, fatigue and carryover effects through a counterbalancing design, all confounding variables could not be accounted for. What participants did in the days leading up to the test may have influenced motivation and hence the results of the experiment. Students who had four hours sleep the previous night and woke up with a hangover, would be less motivated to perform maximally throughout, than say students who had nine hours sleep and ate a healthy breakfast. This could be corrected by monitoring and controlling the lifestyle of participants leading up to the event, but was impractical for this test.
Though we can conclude from this experiment, that our sample performed better in a maximal countermovement vertical jump, with 3kg weights than without weights, further research would explain more. The individual variances between subjects suggest that there may be an optimum weight which maximises jump height, specific to the individual. To achieve this, an experiment could be run whereby subjects jump with external weights as a percentage of their body mass (e.g. 1%, 2%, 3% of body mass), rather than specified weights (e.g. 1.5kg, 3kg as in this experiment). This would require a wider range of wrist weights than was available for the purpose of this experiment, but may provide an insight into why such individual variances were present. It may also explain why there was little difference between the 0kg and 1.5kg conditions (the weight change may have been too small to impact performance).
One question that arose from this experiment was that of how the location of external weights impacts on jump performance. Future research could be conducted to compare how the exact location of external weights influences jump height. Though the studies that have been done suggest that wrist weights have a positive influence on jump height, and that upper body and weights, a negative one, further testing on larger samples with a range of body landmarks, could confirm this concept.
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