BedZED – South London, Inglaterra: varios materiales reciclados

4.4.1 Within-session variability and reliability

Table 4.1: Descriptive (mean ± standard deviations) and reliability statistics, within testing days for jump height for CMJ, SJ and SLDJ

Leg Trial 1 (cm) Trial 2 (cm) ICC SEM (cm) SDD (cm) CMJ 39.40 ± 3.40 39.32 ± 2.94 0.938* 0.17 0.49 (1.3%) SJ 35.10 ± 3.81 34.75 ± 3.79 0.954* 0.23 0.65 (1.9%) SLDJ Left 22.70 ± 3.05 23.56 ± 3.07 0.759 0.36 1.01 (4.4%) Right 23.96 ± 2.89 22.73 ± 3.25 0.445 0.42 1.17 (5.0%) *Reliability significant (p<0.001)

Within-session reliability for CMJ height demonstrated high reliability (Table 4.1), which is also illustrated within Figure 4.1, with similar reliability for SJ performance (Table 4.1, Figure 4.2).

Figure 4.2: Bland-Altman plot for SJ within session one

Within-session SLDJ performance demonstrated moderate reliability (Table 4.1), which is also illustrated within Figure 4.3. Right leg performances showed low reliability (Table 4.1), which is also illustrated within Figure 4.4.

Figure 4.3: Bland-Altman plot for SLDJL within session one

4.4.2 Between-session

Between-session reliability was high for the CMJ, yet significant differences were noted between testing days one and two (Table 4.2). Between-session reliability in the SJ showed high reliability, with trivial and non-significant difference between days (Table 4.2). SLDJ also showed moderate reliability for both left leg and the right leg, with small to trivial effect sizes that were non-significant between days (Table 4.2).

Table 4.2: Descriptive (mean ± standard deviations) and reliability statistics, between testing days for CMJ, SJ and SLDJ

Jump Day 1

(cm) Day 2 (cm) Day 3 (cm) ICC r Partial eta squared SEM (cm) SDD (cm) CMJ 39.96 ± 3.04 37.91* ± 2.90 38.73 ± 3.69 0.906 0.329 0.23 0.65 (1.7%) SJ 35.49 ± 4.21 37.21 ± 3.73 35.80 ± 3.56 0.866 0.171 0.39 1.08 (3.0%) SLDJ Left 24.26 ± 2.95 23.51 ± 4.62 21.58 ± 4.01 0.875 0.321 0.39 1.09 (4.8%) Right 24.53 ± 2.44 23.63 ± 5.25 19.42 ± 4.36 0.759 0.199 0.65 1.80 (7.9%) * Statistical significance between testing days one and two

The SLDJ-R showed the largest SDD (7.9%), with the lowest SDD being observed in the CMJ (1.7%).

4.5

Discussion

The results of this study are in line with the hypothesis, showing that the CMJ demonstrates the highest reliability within and between sessions, when compared to SJ and SLDJ. CMJ also resulted in the lowest SDD within (1.3%) and between sessions (1.7%), with significant differences noted between session one and session two, although no statistically significant differences were observed between session two and session three. Despite SLDJ-L, SLDJ-R and the SJ showing moderate reliability, the SDDs for these tasks were higher than the CMJ, ranging from 3.0-7.9% between sessions, therefore further supporting the hypothesis that bilateral jumps are more reliable than unilateral jumps.

4.5.1 Within-session

Bilateral jumpsresulted in the most reliable performances within sessions (Table 4.1). Reliability of SLDJ within-session was considered unacceptable (ICC r<0.8), for both left and right leg (Table 4.1). The highest within-session reliability was observed during the SJ (r = 0.954), with the CMJ providing the second most reliable measure (r = 0.938). The higher reliability within-session for bilateral jumps, when compared to unilateral jumps, is likely due to bilateral jump requiring less variation in technique adopted and by these jumps being easier to perform. These results are consistent with other research (Bosquet et al., 2009; Glatthorn et al., 2011), which showed that bilateral jumps using an optical measuring systems are reliable and demonstrates that the athletes can reliably replicate CMJ and SJ performances.

4.5.2 Between-session

Between-session reliability followed a similar pattern to the within-session data, yet CMJ appeared as the most reliable (r = 0.906), with significant differences noted between session one and session two, although no statistically significant differences were observed between session two and session three. Between sessions, the SLDJ-R was considered unreliable (r =

0.759), yet SLDJ-L was considered reliable (r = 0.875) (Table 4.2), with no significant

differences observed between days. Despite a significant difference existing between testing day one and testing day two for performance of CMJ, one could conclude that a learning effect does not exist, as the values decrease between day one and testing day two. In addition, when considering the effect size presented for CMJ is trivial (Partial eta squared = 0.329), the significant differences noted between session one and session two could be questioned. The reasons for this difference could perhaps be explained by the CMJ strategy employed by the players. The depth that players moved to on testing day one and testing day two may have differed despite attempts made to standardise the protocol, yet this is not considered a concern as this study wanted to identify variation across testing days.

As reported in similar research assessing jump performances using the OptoJump, Glatthorn et al. (2011) considered OptoJump to be reliable for detecting changes in longitudinal assessments verifying the effectiveness of training programs, when assessing CMJ and SJ. Glatthorn et al. (2011) noted high ICC values (mean 0.985) and random errors averaged 2.81 cm (2.7%). Within this study, SDD was noted as 0.65 cm (1.7%) for CMJ and 1.08 cm (3.0%) for SJ. When trying to identify NMF using CMJ, jump height, assessed from flight time using the force plate, has been considered to be the most precise and reliable instrument. However, in many team- based scenarios a force plate is not readily available, therefore the OptoJump would be the next best alternative, with a difference of greater than 0.49 cm (1.3%) signifying a meaningful change within-session and a difference of greater than 0.65 cm (1.7%) signifying a meaningful change between session. Despite differences existing between session one and session two, the sensitivity identified for CMJ (0.65 cm; 1.7%) is a positive finding of this research and one that should be considered by practitioners.

4.5.3 Limitations of this study

The small sample size within this study could be considered a limitation, yet the implementation of effect size calculation alongside RMANOVA in accordance with

recommendations by Buchheit (2016) to assess magnitude dispute this. The trivial effect size findings in this study therefore further supports the use of this small sample size utilising elite rugby union players. Another possible limitation of this study surrounds the self-selected jump protocol for all jumps by the players. Players were noted to adopt differing jump techniques, mainly whereby; depth of both SJ and CMJ on the downward phase varied and width of stance was individually selected which could have altered results. In addition, the technique adopted during the SLDJ-L and SLDJ-R differed mostly on the start of the jump were some players were noted to “drop off” the box and some were noted to “jump off” the box onto the landing surface below. It, however, could be argued that this variability in jump technique improved the ecological validity of this study, as not all players would move in the same manner possibly due to innate locomotion skills developed from an early age.

4.6

Practical Applications

Despite unilateral jumps being likely to identify NMF more easily, results from this research question their reliability. The large discrepancies in results for unilateral jumps, mainly associated with participant technique adopted, mean that bilateral jumps should be used for performance assessment instead of unilateral, with CMJ being the jump modality that would produce the most reliable measure of performance. A change of 0.65 cm (1.7%) can be