Is a Bimodal Force-Time Curve Related to Countermovement Jump Performance?

Abstract

A countermovement jump (CMJ) represents one of the most frequently used performance tests for monitoring neuromuscular function in athletes. An often-overlooked feature that may provide some useful diagnostic information is the actual shape of the force-time curve. The aim of this study was therefore to consider how the shape of the force-time curve influences jump performance. Thirty-three male rugby union players performed two CMJs on a force plate, with discrete variables and continuous curve analysis used. The subjects were dichotomized based on shape of the force-time curve during the propulsion phase and by jump height. The differences between the unimodal and bimodal groups were unclear for jump height (ES = 0.28, ±0.58) and reactive strength index-modified (ES = −0.30, ±0.59). A substantial difference between high (40.2 ± 2.9 cm) and low (31.2 ± 3.2 cm) jumpers only existed in the late propulsion phase by 79.0% to 97.0% of the normalized force-time curve. A bimodal force-time curve is not representative of an optimal pattern of performance and simply reflects an inefficient stretch-shortening cycle. The inter-individual variability that exists in braking COM displacement renders temporal phase analysis impractical in cross-sectional type studies.

Differences Between Bimodal and Unimodal Force-time Curves During Countermovement Jump

“…The aforementioned outcomes of the current study contradicted a study by Kennedy et al [21] reporting that the DPC did not represent an optimal pattern of CMJ performance and it could be characterized as an ineffective SSC. The discrepancy could be due to the instruction differences between to "jump as high as possible" [21] and "jump as fast and as high as possible" [22] for the participants. The different instructions could alter the utilized movement strategies [47].…”

“…The instruction may not the only factor causing differences in the DPC and SPC. The outcome found in the DPC with larger hip, knee and ankle flexion angular displacements compared to the SPC in the current study was similar to that of larger braking center of mass displacement in the study by Kennedy et al [21]. The current study suggested that the kinematic features combined with the aforementioned hip, knee and ankle (proximal-to-distal) extensors exertion sequence might cause the GRF signal to depress momentarily and thus provide two distinct peaks inferring the importance of the pattern of multi-joint force application and coordination for a good CMJ performance [17].…”

“…The different instructions could alter the utilized movement strategies [47]. The instruction of "to jump as high as possible" may confound the outcomes of the jump height and ratio of negative to positive impulse observed by Kennedy et al [21] which pointing out that the smaller the ratio, the higher the jump [17]. The CMJ is one of typical SSC exercises requiring fast movement with a quick downward countermovement followed by a rapid upward jump [5,6].…”

“…Nevertheless, both instructions can lead to DPC or SPC [21,22]. The instruction may not the only factor causing differences in the DPC and SPC.…”

“…Previous studies speculated the braking center of mass displacement [21] and instructions to "jump as high as possible" and "jump as fast and as high as possible" for the participants [21,22] as causing differences in the SPC and DPC. Nevertheless, they have not clearly addressed the following questions.…”