The Relationship Between The Eccentric Utilization Ratio, Reactive Strength, And Pre-Stretch Augmentation And Selected Dynamic And Isometric Muscle Actions.

Abstract

The ability to use the stretch shortening cycle (SSC) is essential for many sporting activities. There are several approaches by which to assess the SSC. These include the eccentric utilization ratio (EUR), the reactive strength calculation (RSC), and the percent pre-stretch augmentation (PPA). These measures are typically quantified for vertical jump displacements and power outputs. The assessment of the SSC activity via jumping activities may yield valuable information of the athletes training status and potential training interventions to improve SSC performance. To determine if EUR, RSC and PPA are related to dynamic and isometric muscle actions. Twenty seven college track athletes (age = 19.6 ± 1.0 y; body mass = 83.0 ± 25.2 kg; height = 176.9 ± 8.8 cm) performed three types of countermovement vertical jumps (CMJ) and static vertical jumps (SJ) on a force plate. Both CMJ and SJ were performed in unloaded and loaded (11 kg and 20 kg) conditions. All jump data were analyzed for vertical displacement, peak force (PF), and rate of force development (RFD). The EUR (CMJ/SJ), RSC (CMJ-SJ), and PPA ((CMJ-SJ)/SJ) × 100) were calculated for jump height, peak power, and peak force Additionally, subjects performed 2 isometric mid-thigh pull with previously established methods. The isometric mid-thigh pulls were analyzed for PF and RFD. Finally, each subject performed a one repetition maximum back squat test (1-RM) and a maximal ball throw test. There were no significant correlations between the EUR (jump height, PP, PF) for loaded or unloaded jumps and back squat, ball throw, isometric PF, and RFD. All EUR values were above 1, which is indicative of well trained athletes. Significant inverse relationships were found between the PPA calculation for PF during the unloaded condition and squat 1-RM (r = −0.85), ball throw distance (r = −0.74), and isometric PF (r = −0.55). Additionally, during the loaded conditions (11 and 20 kg) the PPA calculation for PF was significantly correlated with the back squat 1-RM (11 kg: r = −0.89; 20kg: r = −0.81), ball throw distance (11 kg: r = −0.824; 20kg: r = −0.65), isometric PF (11kg:r = −0.60; 20kg: r = −0.56), and the isometric RFD (11kg: r = −0.43; 20kg:r = −0.36). The PPA calculation for peak power during the loaded conditions was significantly correlated with the 1-RM back squat (11kg; r = −0.89; 20kg: r = −0.62), ball throw (11kg: r = −0.72; 20kg: r = −0.56), isometric PF (11kg: r = −0.47; 20kg:r = −0.40), isometric RFD (11kg: r = −0.43; 20kg: r = −0.42). The isometric RFD can be estimated by the equation: RFD = −58168.7 (PPA for PP 11kg) + 10866.415 or RFD = −142636.9 (PPA for PP 20 kg) + 10340.226. This study suggests that unloaded or loaded PPA has a relationship with an athlete's 1-RM in the back squat, the ball throw distance, and isometric PF generating capacity. Additionally, under loaded conditions the PPA appears to be related to the isometric RFD. The utilization of CMJ and SJ testing is common place in strength and conditioning and the data calculated from these measures may yield valuable information about performance capacity. The significant relationship between the 1-RM back squat and PPA suggests that strength is an underlying mechanism in the ability to utilize the SSC. Additionally, the PPA assessment may be useful in predicting the isometric RFD.