title: The effects of training status and exercise intensity on plyometric exercise volume
Creators: name: Cronin, Kevin James
Publisher: name: Western Washington University
Year: 2010

description: <p>The purpose of the present study was to examine the effect of training status and exercise intensity on the volume of repetitions completed before propulsive force output decreases below 90 percent of maximum force output. We also examined the effect of training status and exercise intensity on the change in eccentric rate of force development (E-RFD) and contact time (CT) across exercise repetitions (depicted as the slope of the regression line relating the E-RFD and repetitions, and the slope relating CT for each repetition completed). Thirty subjects were recruited from the university population (15 plyometrically trained and 15 recreationally trained). Testing took place on two separate days. On day one of testing subjects completed a dynamic warm up, jump assessment, 1RM leg press, and six maximal effort jumps. On day two of testing subjects completed a dynamic warm up along with continuous low (counter movement jumps) and moderate (box jumps at 25% of subjects height) intensity plyometric exercises that were randomly assigned. A regression analysis of E-RFD and CT was used to observe the trends across all repetitions for both intensities in both subject groups. Repetitions completed in each condition were broken into quartiles for each subject, and mean quartiles were analyzed for E-RFD and CT to observe the trends between the two groups at each intensity. The statistical analysis used within the present study were two three-way mixed factors analyses of variance (ANOVA) to evaluate the effect of exercise intensity, repetition quartile, and training status on E-RFD and CT. The results of the regression analysis for E-RFD and CT for the CMJ and box jumps revealed that there was a great deal of variability between the recreationally trained and the plyometrically trained subjects when looking that the positive and negative slopes of the regression lines. The quartile analysis for E-RFD and CT revealed difference in the rate of decline in E-RFD and CT between the plyometrically and recreationally trained subjects across the four quartiles. The statistical quartile analysis for E-RFD revealed a significant exercise by quartile interaction (p = .03) with the simple effects revealing a significant difference in ERFD between quartile 3 (p = .01) and quartile 4 (p < .001). The statistical quartile analysis for CT revealed a significant quartile by group interaction (p = .009) with the simple effects revealing a significant effect of quartile on contact time (p = .002) in the recreationally trained group. A significant exercise by group interaction (p = .047) was also revealed with the simple effects showing a significant difference in contact time between exercises in both the plyometrically trained (p = .021) and recreationally trained (p < .001) groups. These findings indicate that there were differences in E-RFD and CT when comparing regression and quartile analysis of the trained and recreationally trained groups at the two different intensities of plyometric exercises. Although, in some instances it was observed that the plyometrically trained subjects 'performed' better than their recreationally trained counterparts, the results of the present study reveal a applicable difference in E-RFD and CT between the third and fourth quartiles among the two groups.</p>