Validity and reliability of My Jump 2^® app to measure the vertical jump on elite women beach volleyball players

Introduction

Beach volleyball is a team sport characterized by its intermittent nature, fluctuating randomly from short periods of maximal or sub-maximal activity to long periods of moderate and low-intensity activity (Arruda & Hespanhol, 2008; Magalhães et al., 2011; Medeiros et al., 2014). This alternating activity nature arise in game actions as jumps, constituting one of the most determining physical-technical elements in beach volleyball performance (Andrade et al., 2020; Medeiros et al., 2014, 2023; Oliveira et al., 2018). Accordingly, literature within beach volleyball scope has pointed out that jump measures can help coaches monitor training load and understand the activity profile of players (Andrade et al., 2020; Medeiros et al., 2023; Oliveira et al., 2018).

Specifically, the countermovement jump (CMJ) has been one of the most popular tests for assessing and monitoring neuromuscular status in volleyball and beach volleyball (Andrade et al., 2020; Batista, RFd & Guerra, 2008; Oliveira et al., 2018; Sheppard et al., 2011; Sheppard & Newton, 2012).

However, most of the investigations conducted so far have evaluated jump height of CMJ on a rigid surface, even in the case of beach volleyball (Andrade et al., 2020; Oliveira et al., 2018). This could bring specificity issues (i.e., ecological validity; Davids, 1988) since the assessment of CMJ on a rigid surface could modify jumping performance (Giatsis et al., 2004; Giatsis, Panoutsakopoulos & Kollias, 2018). For example, beach volleyball players demonstrate performing lower vertical jumping heights when jumping on a sand surface compared to a rigid one (Bisciotti, Ruby & Jaquemod, 2001; Bishop, 2003; Giatsis et al., 2004). However, the kinetics of female beach volleyball players when examined across vertical jump tests executed on sand show a different trend compared to male players (Giatsis et al., 2023).

The compliance of the sand imposes a constraint for an efficient coordinated extension of the lower limb joints and requires higher expenditure of energy to fulfill the demand of maintaining postural stability (Muramatsu et al., 2006; Smith, 2006). As result, reduced application of force and less power production during the propulsion of jumping from a sand surface (Bisciotti, Ruby & Jaquemod, 2001; Bishop, 2003; Giatsis et al., 2004; Impellizzeri et al., 2008).

The assessment of vertical jump height using a force platform (usually via take-off velocity or flight time) might be considered as the gold standard (Garcia-Lopez et al., 2013; Glatthorn et al., 2011; Requena et al., 2012). Although this equipment offers higher levels of accuracy and reliability for CMJ measurement, the device depicts many limitations for measuring in field and real-time conditions. Also, issues related to the portability of force platform, their associated costs, and the technical demands to manage the equipment seem to become it unsuitable for most field-based testing.

In this context, applications (apps) for mobile devices have been suggested as alternative tools to measure vertical jumps (Balsalobre-Fernández, Glaister & Lockey, 2015). Among those, the My Jump2^® app was designed to calculate the jump height from the flight time, which is based on the take-off and landing frames selected by the user (Balsalobre-Fernández, Glaister & Lockey, 2015; Brooks, Benson & Bruce, 2018; Yingling et al., 2018). Both the accuracy and reliability of this app have been tested in different populations, including athletes (Barbalho et al., 2021; Gallardo-Fuentes et al., 2016; Soler-Lopez et al., 2022), elderly (Cruvinel-Cabral et al., 2018a), cerebral palsy soccer players (Coswig et al., 2019), and children (Bogataj et al., 2020). Also, different types of jumps and variables were investigated, including squat jumps, CMJ, drop jumps, flight time, jump height, and asymmetry index (Haynes et al., 2019). Although the My Jump2^® app consistently presented excellent values of reliability and validity when compared to force platforms and jump mats (e.g., Cruvinel-Cabral et al., 2018b; Jimenez-Olmedo et al., 2022; Rago et al., 2018; Soler-Lopez et al., 2022), to date it was not found any scientific investigation that had tested the validity and reliability of the My Jump2^® app to measuring jump height in sand surface. Furthermore, validity and reliability studies had focus in investigate males (Carlos et al., 2015; Thomas et al., 2019). One study showed that the My Jump2^® app had good intra- and inter-session reliability for male and females. The agreement for them were almost perfect (Gallardo-Fuentes et al., 2016). This tool empowers various sports practitioners, including coaches, performance analysts, and teachers, by enabling them to predict injury risks, facilitate talent identification, and seamlessly assess, monitor, and adapt their practices. Moreover, of the My Jump2^® app reveals a reliable tool, it will enable the inclusion of CMJ assessments in sand surface throughout the practice.

Considering the foregoing, the aim of this study was to assess the reliability and validity of the My Jump 2^® app in measuring jump height, flight time, and peak power among elite women beach volleyball players on sand surfaces.

Materials and Methods

Design

This study followed an experimental design that compared the values of six CMJ (Claudino et al., 2016) for each player between the My Jump 2^® app and the gold standard force platform (Bertec-Model FP4060-08-1000, COLUMBUS, OH, USA, sampling frequency of 1,000 Hz). All CMJs were performed without arm swing, and inside a wooden box filled with sand (Fig. 1). Globally, 66 CMJ were accomplished, and all participants were familiarized with CMJ technique before testing. Prior the test, the participants completed a standard 20 min warm-up composed of stationary cycling (Monark 817E bicycle at a constant speed of 5.5 m/s⁻¹ with 0 W load), lower body dynamic stretches, and vertical jumps (Giatsis, Panoutsakopoulos & Kollias, 2018).

Results

Table 1 shows the descriptive statistics of CMJ variables obtained with the My Jump 2^® app (both observers) and force platform. Values are mean ± standard deviation (SD).

Table 2 presents the results between-observer reliability to My Jump 2^® app and, My Jump 2^® app and the force platform for jump height, flight time and peak power. The differences between observers for My Jump 2^® in all variables were very small (ES ranging from 0.03 to 0.05).

The ICC between observers, as well as among the My Jump 2^® app vs force platform, was considered good in relation to jump height and flight time (observers: 0.92 and 0.91, the My Jump 2^® app vs force platform: 0.85 and 0.85). However, in what peak power regards, the ICC was moderate between the My Jump 2^® app and force platform (0.64).

Correlations between two observers for the My Jump 2^® app showed almost perfect relationship (Fig. 2; r = 0.90 to 0.96; R² = 81.00% to 94.00%).

The force platform and the My Jump 2^® app correlations for jump height, flight time and peak power showed large relationship (Fig. 3; r = 0.52 to 0.77; R2 = 28.00% to 60.00%).

Figure 4 shows the results of the agreement analysis between the two observers using the My Jump 2^® app. We did not observe any systematic bias in the variables. The difference between observers showed acceptable values.

The agreement analysis between the My Jump 2^® app and force platform is depicted in Fig. 5. Our analysis did not reveal any systematic bias in the results obtained from either method. However, we did observe larger differences between the methods when compared to the observers.

Discussion

The purpose of this study was to investigate the reliability and validity of the My Jump 2^® app in measuring jump height, flight time, and peak power on the sand surface among elite women beach volleyball players. The study provided evidence that the My Jump 2^® app is a valid and reliable tool for measuring jump height and flight time during a countermovement jump on a sand surface in elite women beach volleyball players.

Given the agreement between observers, the My Jump 2^® app showed to be highly reliable considering the between observers (i.e., inter-reliability). Like other study conducted on rigid surface (Balsalobre-Fernández, Glaister & Lockey, 2015), we found excellent agreement for flight time, jump height and peak power between observers. The mean differences for jump height, flight time, and peak power were only 0.18 cm, 1.59 ms, and 9.76 w, respectively, showing no significant differences for these variables. The Bland-Altman plot also revealed mean differences inter-observers for jump height similar to studies conducted on a rigid surface (Balsalobre-Fernández, Glaister & Lockey, 2015; Jimenez-Olmedo et al., 2022). However, it is noteworthy that a larger limit of agreement was found. Thus, the idea that the app reliability could be significantly impaired by surface softness was not confirmed.

Although we observed less agreement (ICC) between observers and force platform compared to CMJ jump height in rigid surface (0.99 vs 0.85) (Balsalobre-Fernández, Glaister & Lockey, 2015), there was a good agreement between the force platform and the My Jump 2^® app in measuring jump height, and flight time. However, we only found a moderate agreement for peak power (observers vs force platform). We did not find any significant differences between the values obtained for flight time, jump height, and peak power using My Jump 2^® app and the force platform.

The mean difference in jump height between the My Jump 2^® app and the force platform was only 0.32 cm, which was similar to the findings of another study (Gallardo-Fuentes et al., 2016). We also found small mean differences for flight time (5.87 ms) and peak power (−7.04 w). However, the coefficient of determination was very large for jump height and flight time, but only moderate for peak power.

The Bland-Altman plot indicated that the data obtained from the My Jump 2^® app and the force platform were close to the mean difference. The difference in jump height showed a limit of agreement between −4.10 and 4.74, indicating a high level of agreement between the two measurement tools (Martin Bland & Altman, 1986).

Some cautions should be considered while interpreting our findings because of some limitations. Firstly, the jump type can influence in the results. We only assessment the jumps with the hands on the hip. Second, we positioned the phone on 1.5 m from the force platform at floor level and sagittal plane, despite the app recommendations (record the feet from the front). Nevertheless, the height of the recording does not have any impact on the reliability and accuracy of the measurement (Koo & Li, 2016). However, we observed no significant differences between the observers using the My Jump 2^® app or between the My Jump 2^® app and the force platform. Based on these findings, we can suppose that the height of the recording and the sagittal plane did not significantly compromise the measurement. However, we cannot infer whether these adaptations reduce or increase the amount of variance explain by the My Jump 2^® app variables, especially for peak power. Finally, accounting for sand dissipation during take-off could potentially extend the flight time. This arises from athletes executing take-offs on a higher surface level compared to their landing. Future studies could consider recording the video in the sagittal plane to investigate if this would improve the agreement between the measurements and would include another jumps (drop jumps or jumps with free arms).

Conclusions

We concluded that My Jump 2^® app is a valid tool for measuring CMJ jump height and flight time on sand surfaces. However, more caution is needed when measuring peak power. Coaches can utilize the My Jump 2^® app to access jump variability, estimate neuromuscular recovery by analyzing the height of the jump, and monitor changes in jump performance pre- and post-competition.

Supplemental Information