Cameron McLaury1, Jacob Thomas1, Alex Long1, August Bont1, Davis Hale1, Gabriel Sanders2, Will Peveler3, J. Jay Dawes4, Roger Kollock1 1University of Tulsa, Tulsa, Oklahoma; 2Northern Kentucky University, Highland Heights, Kentucky;3Liberty University, Lynchburg, Virginia;4Oklahoma State University, Stillwater, Oklahoma

The rate of musculoskeletal injury in Army Basic Training Recruits is higher than the general army population. Lack of experience carrying heavy loads may be cause of this disparity. PURPOSE: The purpose of this experiment was to determine the difference in vertical ground reaction force (VGRF) between experienced (EXP) and inexperienced (IEXP) load carriers during a drop jump (DJ) task. METHODS: 8men and 3 women were recruited for both the EXP(n=11)and for the IEXP(n=11)condition. Those in the IEXP group have no military experience and were deemed to be recreationally active which was defined as performing weight lifting or cardiovascular activities for at least 30 minutes 2-3 days per week, while those in the EXP group include active duty personnel, reservist and ROTC. Each participant performed 3 trials of a drop jump task from a 30 cm box placed at 10% of the participant’s height from the force plate. The VGRF was collected for the dominant limb and captured at a sampling rate of 1500 Hz. Three DJ trials were performed under two separate conditions: unloaded and loaded. For the unloaded condition, each participant wore shorts, t-shirt, and combat boots. After completing three unloaded DJ trials, the participants were fitted with a 1.6 kg combat helmet, 5.4 kg improved outer tactical vest, and 14 kg rucksack. The participants then performed 3 DJ trials while wearing the military gear. A Mann-Whitney U test was used to examine the difference in VGRF in Newtons (N)between groups for the unloaded condition, while an independent t-test was used to explore the difference between groups for the loaded condition. Alpha level was set at .05. RESULTS: No significant difference in VGRF was found (U = 45.00, p>0.05)between EXP(1742±834.50 N)and IEXP (1783±428.02N) for the unloaded condition. No significant difference (t(20) = 0.720, mean diff =207.71, p>0.05)was found between EXP (2078.49±810.00N) and IEXP(2285.45± 508.37)for the loaded condition. CONCLUSION: Experience with wearing heavy loads did not have a statistically significant effect on DJ VGRF under loaded conditions. However, under loaded conditions the mean difference (207.71 N) in VGRF between groups may be of practical significant. Future research should investigate the effect fatigue may have in exacerbating these difference in VGRF between EXP and IEXP.

ACKNOWLEDGEMENTS: This study was funded in part by The University of Tulsa Kick Start Program and Northern Kentucky University’s Office of Research, Grants and Contracts. The authors would like to acknowledge the Northern Kentucky University Veterans Resource Station. The results of the present study do not constitute endorsement by The University of Tulsa or Northern Kentucky University.

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