The countermovement jump (CMJ) is often used to monitor athletes' performance through the interpretation of metrics derived through force plate data collection, and recent advances in technology now allow technicians of all experience levels to easily collect data. This may introduce procedural variation, such as verbal instruction. In addition, athletes competing in sports that place importance on vertical jumping may possess ingrained movement patterns. The purpose of this study was to evaluate if verbal instruction may disrupt an athlete's natural jump strategy, thus clouding interpretation of CMJ profiles. This study uses repeated-measures design with significance set at 0.05 to evaluate differences in jump variables under 3 different instructional conditions. Twelve female DI volleyball athletes performed 9 total jumps on a force platform, 3 under each condition. The instructions include: "jump as high as possible" (CMJ-H), "jump as fast as possible" (CMJ-F), and "jump to the best of your ability" (CMJ-N). No differences in jump height, braking impulse, and propulsive impulse were observed across conditions (p > 0.05). However, force variables and reactive strength index modified were significantly higher, and temporal variables were significantly lower under CMJ-F compared with CMJ-H and CMJ-N (p < 0.05). In addition, countermovement depth was significantly shallower under CMJ-F. Conversely, no significant differences were observed for any variables between CMJ-H and CMJ-N (p > 0.05). The CMJ-F condition elicits an increase in force production, whereas CMJ-H and CMJ-N elicit an elongation of time. This study indicates the need for procedural consistency regarding the instruction used.
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