Investigation of the factors affecting stretch shortening CYCLE during DROP JUMP

Stretch shortening cycle is analyzed in two categories as fast (<250ms) and slow (>250ms) stretch shortening cycle according to the threshold value of ground contact time obtained during the drop jump test. However, in the literature, there are a limited number of studies on how this norm value, which is expressed as 250 ms, is obtained and which variables affect this norm value. The aim of this study was to (1) determine which variables of force, time, power and force-time interaction variables and muscle-tendon mechanical properties interact with the ground contact time and (2) to investigate whether threshold values of ground contact time differs from 250ms can be obtained based on the findings obtained. Force, time, power and force-time interaction variables were obtained during the drop jump (KISTLER 9260AA6 model, Switzerland) performed from the optimal drop height. The variables related to muscle-tendon mechanical properties, which are thought to affect the ground contact time, were evaluated by elastography (Siemens Acuson S3000). Forty-six men (age: 22.02±1.41 years; height: 179.93±7.04 cm; body weight: 76.39±1.11 kg), who had not trained for at least 2 years and/or exercised for at most 6 hours per week, voluntarily participated in the study. Pearson (r) and Spearman (rho) correlation test were used to analyze the relationship between the variables and length of ground contact time. For the classification determined by using the variables thought to be in interaction with the ground contact time, the regression tree method was analyzed and the threshold values of the ground contact time with the lowest RMSEA value were taken as the basis for groupings. The research group was regrouped according to the determined threshold values. One-way ANOVA, Welch ANOVA, and Kruskal-Wallis test were applied to evaluate the differences between variables and groups. In this study, 95% confidence interval was accepted. According to the findings of the study, significant correlation levels were found between the ground contact time and the variables of force, time, power and force-time interaction and muscle-tendon mechanical properties (p<0.05). As a result of the analysis performed according to the classification and regression tree method with RStudio, the reactive strength index value with the lowest RMSEA value was taken into consideration and the threshold value of the corresponding residence time was determined as a result of the analysis (GCT<188 ms, 188≤GCT<222 and GCT≥222 ms). According to intergroup comparisons, it was observed that force, time, power variables and Achilles tendon length were different in at least two groups. As a conclusion, it was found that 250 ms can be analysed with more than one threshold value instead of using 250 ms as a single threshold. It is recommended that appropriate thresholds be determined and analyzed in different populations.