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EXAMINING COUNTER-MOVEMENT JUMP HEIGHT USING A DIGITAL CONTACT MAT COMPARED TO FORCE PLATES

Abstract

BACKGROUND: Jump testing is commonly used to assess return to sport for those recovering from ACL injury and repair. In a previous study, this testing method was praised as it stated vertical jump performance as more representative of a metric for knee function in healthy individuals than horizontal hop performance. Previous research has found the Just Jump system to slightly overestimate jump height while still maintaining high correlation rates with the gold standard Force Plate and only slight variations reported in the twos height measurements. The purpose of this research was to assess differences in jump height using a digital contact mat (Just Jump System, Probotics, Huntsville, Alabama, USA) versus force plates (Hawkins Dynamic, ME, US). It was hypothesized that there would not be significant differences between devices given both use flight time to calculate jump height. METHODS: 38 high level soccer players (M: n=18, age (yrs)= 21.5 ± 1.6, %BF= 10.7 ± 3.5; W: n =20, age (yrs)= 20.9 ± 2.1, %BF= 20.4 ± 4.3) participated in this experimental study. Each participant executed power performance on a contact mat (Just Jump System, Probotics, Huntsville, Alabama, USA) and force plates (Hawkins Dynamic, ME, US). Testing measures included bilateral countermovement jumps (CMJ) and bilateral drop jumps (DJ). Participants repeated each jump twice, if the two jumps differed by greater than 10% a third jump was performed, and the best jump was used for analysis. All performance metrics were analyzed using a paired t-test and Pearson correlations between contact mat vs force plate. Statistical significance was set at α=0.05. RESULTS: Significant differences in jump height were observed in CMJ and DJ (P<0.05) between the jump mat and force plate data with the Jump Mat data being higher on average (JM CMJ = 18.3 ± 3.2, FP CMJ = 12.3 ± 2.5; JM DJ = 18.5 ± 2.7, FP DJ = 11.6 ± 3.2). For both the CMJ and DJ, a strong correlation was found. More specifically, there was a strong positive linear relationship between the two testing methods for both CMJ and DJ (r=0.96 and r=0.68 respectively).DISCUSSION: The significant difference between the two testing methods paired with the strong positive relationship indicates strong reliability, albeit poor validity, of the digital contact mat compared to force plates. This means that these testing methods are not fully interchangeable in practice, as the digital contact mat continuously overestimates jump height compared to force plates. Given this, researchers should be cautious when selecting which method to use, particularly when absolute values are critical values in decision making or assessment. As for further investigations, the source of the significant difference between the two methods should be further evaluated as well as previously developed equations aimed at created a more equal comparison between devices.

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