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A kinetic analysis of a series of drop jump : the effect of drop height and rest periods
Author
Tang, Yew Seng
Supervisor
Raynor, Annette
Abstract
This study was composed of three parts with the overall aim being to investigate the effects of drop height and rest period on the kinetic measures associated with the performance of 40 drop jumps, a commonly used stretch-shortening cycle (SSC) activity for the development of strength and power The purpose of Part One was to determine an appropriate drop height from between 40 to 70 cm; Part Two investigated the relationship between the kinetic variables and isokinetic strength and power measures and functional estimates of muscular power; and Part Three investigated the effect of a one minute rest between each set of ten drop jumps on the kinetic measures of 40 drop jumps.
Eight male subjects aged 18.7 2 0.5 years were selected from a Singapore Junior College track and field team to participate in this study with all subjects considered to be sprint and jump specialists In Part One, subjects performed one set of 10 drop jumps from each of four heights, specifically, 40 cm (DJ40), 50 cm (DJ50), 60 cm (DJ60) and 70 cm (DJ70). The ground contact time, flight time and peak vertical ground reaction forces were measured from a Kistler mobile force platform (Model 9286) with the rebound height being subsequently calculated. Results of paired t-tests revealed no significant difference in the mean rebound height across the four drop heights, however; based on ground contact times and vertical ground reaction forces the use of a 40 to 50 cm drop height was suggested. A drop height of 50 cm was therefore selected as it was thought this would elicit maximal benefits with respect to the SSC movement, while still being considered safe.
Having established the drop height, one week later subjects were requested to complete 40 consecutive drop jumps and one week later again, subjects completed 40 drop jumps with a one minute rest period between each set of ten jumps. Changes in the kinetic variables of coupling time, ground contact time, rebound height, peak vertical ground reaction force, magnitude of first impact spike and angle of knee flexion were measured across the 40 drop jumps for each condition.
The kinetic variables analyzed from the 40 consecutive drop jumps were correlated with the maximum peak torque and average power measurements obtained during a concentric-eccentric knee extension-flexion task on a Cybex 6000 dynamometer at 180 and 240 degrees per second and functional estimates of muscular power (50 m sprint time, vertical jump height and power). Pearson product-moment correlation analysis revealed a positive relationship between the coupling time of the drop jump and the two performance measures of 50 m sprint and vertical jump power, suggesting that subjects may have been using a greater proportion of slow-twitch muscle fibres when performing these activities. In addition, it was suggested that the isokinetic measurements obtained may not be good indicators of drop jump ability.
The final part of this study investigated the effect of a rest period on the kinetic changes across the 40 drop jumps. Changes in the kinetic variables (as measured in Part Two) were analyzed using a MANOVA statistics for the two different treatments across the 40 jumps. A Student's t-test was subsequently used to determine the differences in the kinetic variables between the two treatments.
No significant changes were observed in the kinetic variables measured across the 40 drop jumps in either condition, with no significant difference in the kinetic variables between the two conditions. Despite this, there was a trend of reduced variability in the kinetic measures associated with the drop jump series with one minute rest intervals, compared to the 40 consecutive drop jumps.
In conclusion, this study recommends the use of a 40 to 50 cm drop height when implementing drop jump training. In addition, despite no significant changes being observed in the kinetic variables of interest, the reduced variability observed when the drop jumps were performed with a one minute rest interval, may suggest that this protocol is beneficial in minimizing "undesirable" jumps when performing a series of drop jumps. Lastly, coupling time was found to be closely related to speed and power performance and thus further studies should investigate the possible relationship between coupling time and muscle fibre composition. If a relationship is established between these variables, this simple kinetic measure may be used in preference to the current invasive technique of muscle biopsy for the prediction of muscle fibre composition.
Eight male subjects aged 18.7 2 0.5 years were selected from a Singapore Junior College track and field team to participate in this study with all subjects considered to be sprint and jump specialists In Part One, subjects performed one set of 10 drop jumps from each of four heights, specifically, 40 cm (DJ40), 50 cm (DJ50), 60 cm (DJ60) and 70 cm (DJ70). The ground contact time, flight time and peak vertical ground reaction forces were measured from a Kistler mobile force platform (Model 9286) with the rebound height being subsequently calculated. Results of paired t-tests revealed no significant difference in the mean rebound height across the four drop heights, however; based on ground contact times and vertical ground reaction forces the use of a 40 to 50 cm drop height was suggested. A drop height of 50 cm was therefore selected as it was thought this would elicit maximal benefits with respect to the SSC movement, while still being considered safe.
Having established the drop height, one week later subjects were requested to complete 40 consecutive drop jumps and one week later again, subjects completed 40 drop jumps with a one minute rest period between each set of ten jumps. Changes in the kinetic variables of coupling time, ground contact time, rebound height, peak vertical ground reaction force, magnitude of first impact spike and angle of knee flexion were measured across the 40 drop jumps for each condition.
The kinetic variables analyzed from the 40 consecutive drop jumps were correlated with the maximum peak torque and average power measurements obtained during a concentric-eccentric knee extension-flexion task on a Cybex 6000 dynamometer at 180 and 240 degrees per second and functional estimates of muscular power (50 m sprint time, vertical jump height and power). Pearson product-moment correlation analysis revealed a positive relationship between the coupling time of the drop jump and the two performance measures of 50 m sprint and vertical jump power, suggesting that subjects may have been using a greater proportion of slow-twitch muscle fibres when performing these activities. In addition, it was suggested that the isokinetic measurements obtained may not be good indicators of drop jump ability.
The final part of this study investigated the effect of a rest period on the kinetic changes across the 40 drop jumps. Changes in the kinetic variables (as measured in Part Two) were analyzed using a MANOVA statistics for the two different treatments across the 40 jumps. A Student's t-test was subsequently used to determine the differences in the kinetic variables between the two treatments.
No significant changes were observed in the kinetic variables measured across the 40 drop jumps in either condition, with no significant difference in the kinetic variables between the two conditions. Despite this, there was a trend of reduced variability in the kinetic measures associated with the drop jump series with one minute rest intervals, compared to the 40 consecutive drop jumps.
In conclusion, this study recommends the use of a 40 to 50 cm drop height when implementing drop jump training. In addition, despite no significant changes being observed in the kinetic variables of interest, the reduced variability observed when the drop jumps were performed with a one minute rest interval, may suggest that this protocol is beneficial in minimizing "undesirable" jumps when performing a series of drop jumps. Lastly, coupling time was found to be closely related to speed and power performance and thus further studies should investigate the possible relationship between coupling time and muscle fibre composition. If a relationship is established between these variables, this simple kinetic measure may be used in preference to the current invasive technique of muscle biopsy for the prediction of muscle fibre composition.
Date Issued
1996
Call Number
GV481 Tan
Date Submitted
1996