Statistical technique. Systematic error or bias (validity)

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1 Reliability of the Vertimetric vertical jump measurement device Prepared by Dr. Matt Beekley (University of Indianapolis) and Dr. Jim Brown (Safe Responder, LLC) INTRODUCTION Vertical jump is a measurement used to infer leg power in subjects. Vertical jump height is also an important component of sport performance, e.g. basketball and volleyball. Vertical jump height can be measured in a variety of methods, including video recordings, contact mat using flight time, force plate using double integration of vertical reaction force, and Vertec device that a subject must jump up and tap. Most (but not all) references refer to the force plate method as the gold standard (Linthorne 2001, Casartelli, et al. 2010). However, this method is expensive and its use outside the laboratory is limited. The current study was undertaken to examine the reliability of a new device (Vertimetric) which uses an accelerometer to measure vertical jump height. METHODS 12 male and female college age subjects, half NCAA Div. II athletes, were recruited for the study. Subjects performed 5 jumps on two different days, with at least 48 hrs recovery between jump testing. Subjects stood on a Kistler Force Plate, on top of which was a Just Jump mat. A Vertec device was aligned next to the force plate. Subjects then wore the Vertimemtric accelerometer on their dominant leg, aligned as instructed according to Lafayette Instruments. All jumps were counter movement jumps. Subjects were verbally encouraged to jump as high as possible for all jumps. A warm up was given and practice jumps were allowed. Data analysis Numerous techniques have been suggested for analysis of reliability but unfortunately no consensus has been reached (see Atkinson and Nevill 1998). The current methods were suggested by Atkinson and Nevill Measure Systematic error or bias (validity) Relative reliability Relative (test retest) reliability Absolute reliability Absolute reliability Statistical technique ANOVA Pearson product moment correlation (R) Intraclass correlation coefficient (ICC) Standard error of mean (SEM) Coefficient of variation (CV) See the following papers for formulas, rationale, and application of the above measures and statistical techniques: Atkinson and Nevill 1998, Weir Analysis was done using SPSS or Excel. RESULTS AND DISCUSSION Systematic error or bias Table 1. Mean jump heights across devices (in cm, N=12 subjects, 120 total jumps from 2 visits of 5 jumps each) Force Plate Vertimetric Just Jump Vertec Mean SD

2 Statistical analysis (ANOVA) revealed that Just Jump and Vertec means were not significantly different; Vertimetric was significantly lower than Just Jump or Vertec, but significantly higher than Force Plate. However, it is well known that the Force Plate method produces somewhat lower results compared to other measures, and that the Just Jump method produces somewhat higher results compared to other methods (Linthorne, ). The fact that the Vertimetric device produced results in between these methods is encouraging. Relative reliability (note: figures 1 and 2 found after references) Figure 1 (plot of Force Plate jump heights vs. Vertimetric device jump heights) indicates fairly good agreement between the gold standard e.g. the Force Plate, and the Vertimetric device. Again, it is well known that Force Plate produces somewhat lower measurements of vertical jump height compared to other methods. Figure 1 also indicates some heteroscedasticity even though statistical methods to indicate this were not significant, e.g. skewness to standard error of skewness ratios, were low (< 2.0, data not shown). Heteroscedasticity in a data set occurs when subjects who perform better (i.e. higher jumpers) demonstrate more variability in scores when compared to subjects who perform worse (i.e. lower jumpers). Similar findings of heteroscedasticity have been shown previously using the force plate vs. another standard in vertical jump data sets (i.e. Casartelli et al. 2010, Nuzzo et al. 2011). Figure 2 (plot of Vertec jump heights vs. Vertimetric device jump heights) also indicates fairly good agreement between another purported gold standard e.g. Vertec device, and the Vertimetric device. These two devices were closer in measurement and the intercept approaches 0 here. Interestingly, the heteroscedasticity also disappears, which has also been found by other authors using the Vertec device (Nuzzo et al. 2011). Note: all Pearson r values on Fig. 1 and 2 were significant at the 0.05 significance level. Relative (test retest inter and intra visit) reliability Table 2. Intervisit relative reliability (between visit 1 and visit 2) Device ICC Vertimetric 0.91 Force Plate 0.90 Vertec 0.85 Just Jump 0.89 Table 3. Intravisit relative reliability (across 5 jumps for visit 1) Device ICC Vertimetric 0.93 Force Plate 0.95 Vertec 0.88 Just Jump 0.92

3 Absolute (test retest inter and intra visit) reliability Table 4. Intervisit absolute reliability (between visit 1 and visit 2) Device SEM (cm) CV (%) Vertimetric Force Plate Vertec Just Jump Table 5. Intravisit absolute reliability (across 5 jumps for visit 1) Device SEM (cm) CV (%) Vertimetric Force Plate Vertec Just Jump Although there is much debate regarding the appropriate statistics to use for reliability studies and how to interpret them, some have suggested that an ICC 0.90 and a CV < 10% (Atkinson and Nevill 1998, Nuzzo et al. 2011) indicates good reliability. If one accepts these criteria, the current data suggest the Vertimetric device is a reliable device for the measurement of vertical jump height in both groups of jumps and across separate visits. OVERALL CONCLUSIONS It should be stressed that it is well known that differing methodologies to measure vertical jump height result in slightly different values of jump heights. This means that these methods are not valid as compared to each other, though they are commonly used. Related to this fact, currently in the literature there is no consensus about which methodology is a gold standard : some have suggested the force platform (Linthorne 2001,), use of video during jumps (Dias et al. 2011, Menzel et al. 2010), or the Vertec device (Casartelli, et al. 2010). This makes the conclusions one can reach about a new device to measure vertical jump height, particularly in regards to validity, that much more tentative. However, based on the data contained in this report, one can conclude that the Vertimetric device, while not in exact agreement with other methods of measuring vertical jump height (i.e. not considered valid), is a reliable device to measure vertical jump height. In further support of this conclusion, a recent publication (Casartelli, et al. 2010) examining a similar device found results almost identical to ours: the accelerometric device measured lower than the Just Jump and Vertec devices. Other measures of reliability in that research are similar to the current findings. These results taken together suggest that the Vertimetric device is a reliable device to measure vertical jump height. The Vertimetric device can be used to assess athletic performance, especially for sports in which vertical jumps are important like basketball and volleyball, and can be used to reliably measure vertical jump height in active and sedentary populations, which can be useful for measurements across time periods e.g. in response to training or rehabilitation programs.

4 REFERENCES Atkinson G, and Nevill AM. Statistical methods for assessing measurement error (reliability) in variables relevant to sports medicine. Sports Medicine 26(4): , 1998 Casartelli N, Muller R, Maffiuletti NA. Validity and reliability of the Myotest accelerometric system for the assessment of vertical jump height. Journal of Strength and Conditioning Research 24(11): , 2010 Dias JA, Dal Pupo J, Reis DC, Borges L, Santos SG, Moro ARP, Borges, NG. Validity of two methods for estimation of vertical jump height. Journal of Strength and Conditioning Research 25(7): , 2011 Leard JS, Cirillo MA, Katsnelson E, Kimiatek DA, Miller TW, Trebincevic K, Garbalosa JC. Validity of two alternative systems for measuring vertical jump height. Journal of Strength and Conditioning Research 21(4): , 2007 Linthorne NP. Analysis of standing vertical jumps using a force platform. American Journal of Physics 69(11): , Menzel, HJ, Chagas MH, Szmuchrowski LA, Araujo SR, Campos CE, Giannetti MR. Usefulness of the jump and reach test in assessment of vertical jump performance. Perceptual and Motor Skills 110(1): , 2010 Nuzzo JL, Anning JH, Scharfenber JM. The reliability of three devices used for measuring vertical jump height. Journal of Strength and Conditioning Research 25(9): , 2011 Weir, J.P. Quantifying test retest reliability using the intraclass correlation coefficient and the SEM. Journal of Strength and Conditioning Research 19(1): , 2005

5 Figure 1. Graph of vertical jump height in cm from Force Plate (x axis) vs. Vertimetric device (y axis). Pearson correlation was statistically significant at the p < 0.05 level.

6 Figure 2. Graph of vertical jump height in cm from Vertec device (x axis) vs. Vertimetric device (y axis). Pearson correlation was statistically significant at the p < 0.05 level.

TESTING VERT ACCELEROMETER TO IDENTIFY VALIDITY AND RELIABILITY WHEN COMPARED TO SWITCH MAT

East Tennessee State University Digital Commons @ East Tennessee State University Undergraduate Honors Theses Student Works 12-2017 TESTING VERT ACCELEROMETER TO IDENTIFY VALIDITY AND RELIABILITY WHEN