Changes in the force-time curve during a repeat power ability assessment using loaded countermovement jumps.

BACKGROUND

Repeat power ability (RPA) assessments traditionally use discrete variables, such as peak power output, to quantify the change in performance across a series of jumps. Rather than using a discrete variable, the analysis of the entire force-time curve may provide additional insight into RPA performance. The aims of this study were to (1) analyse changes in the force-time curve recorded during an RPA assessment using statistical parametric mapping (SPM) and (2) compare the differences in the force-time curve between participants with low and high RPA scores, as quantified by traditional analysis.

MATERIALS AND METHODS

Eleven well-trained field hockey players performed an RPA assessment consisting of 20 loaded countermovement jumps with a 30% one repetition maximum half squat load (LCMJ20). Mean force-time series data was normalized to 100% of the movement duration and analysed using SPM. Peak power output for each jump was also derived from the force-time data and a percent decrement score calculated for jumps 2 to 19 (RPA). An SPM one-way ANOVA with significance accepted at  = 0.05, was used to identify the change in the force-time curve over three distinct series of jumps across the LCMJ20 (series 1 = jumps 2-5, series 2 = jumps 9-12 and series 3 = jumps 16-19). A secondary analysis, using an independent -test with significance accepted at  < 0.001, was also used to identify differences in the force-time curve between participants with low and high RPA.

RESULTS

Propulsive forces were significantly lower ( < 0.001) between 74-98% of the movement compared to 0-73% for changes recorded during the LCMJ20. analysis identified the greatest differences to occur between jump series 1 and jump series 2 ( < 0.001) at 70-98% of the movement and between jump series 1 and jump series 3 ( < 0.001) at 86-99% of the movement. No significant differences were found between jump series 2 and jump series 3. Significant differences ( < 0.001) in both the braking phase at 44-48% of the jump and the propulsive phase at 74-94% of the jump were identified when participants were classified based on low or high RPA scores (with low scores representing an enhanced ability to maintain peak power output than high scores).

CONCLUSION

A reduction in force during the late propulsive phase is evident as the LCMJ20 progresses. SPM analysis provides refined insight into where changes in the force-time curve occur during performance of the LCMJ20. Participants with the lower RPA scores displayed both larger braking and propulsive forces across the LCMJ20 assessment.