## 4 Discussion
In the current study, great emphasis was given to familiarizing the participants with a suitable DJ technique in a separate familiarization session. In general, we were aiming to train the participants to keep the ground contact time at \(\leq\)250 ms, as suggested by [PERSON] et al. [10], for a reactive DJ. Although [PERSON] et al. [12] also familiarized their subjects, there were differences when comparing the studies of [PERSON] et al. [12], [PERSON] et al. [11], and the current study. While a relatively short contact time during the DJ was seen in the participants in the current study (from 133 ms to 225 ms), in the studies of [PERSON] et al. [12] and [PERSON] et al. [11], the participants' ground contact time during the DJ ranged from 148 ms to 290 ms and from 150 ms to 350 ms, respectively. Therefore, one could assume that the participants in the current study might be better conditioned to the DJ, which likely resulted in a better (i.e., more economical) DJ technique. Hence, it could be assumed that the participants in the current study did not necessarily need such stiffness in either the muscle or tendon to perform a proper DJ, as seen in previous studies [11; 12]. Consequently, future studies should investigate the relationship between tissue stiffness (i.e., muscle stiffness and tendon stiffness) and DJ performance in participants that are familiarized with DJs, and in participants that are not familiarized with DJs. Moreover, as suggested by [PERSON] et al. [31], the sample in the current study might have been too homogeneous in both stiffness values and jump performance values to find a significant correlation between these variables. This is underlined by, e.g., the smaller range of contact times assessed in the current study (92 ms), compared with the studies of [PERSON] et al. [12] and [PERSON] et al. [11], with 142 ms and 200 ms, respectively. A further possible explanation for the contradictory findings between the previous studies [11; 12] and the current study might be in the different methods used to assess tissue stiffness. [PERSON] et al. [12] used shear wave elastography to assess muscle stiffness and [PERSON] et al. [11] used force elongation curves to assess tendon stiffness. The technique used in the current study was myotonometry, by the use of a Myoton device. Excellent reliability (i.e., ICC > 0.75; [32]) of the muscle and tendon stiffness assessment with the Myoton device has been reported in previous studies which assessed the reliability in these MTUs (quads: [33; 34]; calf: [24; 34]). Moreover, the validity of the Myoton device was also confirmed by a previous study [24]. Good correlation between shear wave elastography and the Myoton device has also been reported recently [34]. Hence, it can be assumed that the Myoton device is valid, reliable, and will likely result in the same outcome as the outcome obtained with other techniques, such as ultrasonic shear wave elastography. With regard to CMJ performance, we did not find any significant correlation with patellar tendon stiffness or rectus femoris, vastus medialis, or vastus lateralis stiffness. However, [PERSON] et al. [16] reported a large positive correlation (r = 0.55) between the stiffness of the musculotendinous structure of the vastus lateralis muscles and CMJ height in 16 highly trained athletes. Again, the different findings in the study by [PERSON] et al. [16] and the current study might be explained by the different methods used for the stiffness assessment (active force elongation curves via dynamometry and ultrasound vs. passive Myoton measurements) and/or by the different populations (well-trained vs. moderately active) investigated. Consequently, it is likely that variables other than muscle or tendon stiffness of the quadriceps MTU are related to CMJ performance. For example, [PERSON] and [PERSON] [35] reported that strength and the rate of force development are predictors for good CMJ performance, irrespective of the technique used (i.e., starting position).