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.
Highlights
Vertical jumping is a fundamental movement skill that develops during early childhood and is a key component of many sports
The main findings of the present study indicate that a bimodal force-time curve does not represent an optimal pattern of countermovement jump (CMJ) performance and it reflects the adoption of a movement strategy that can be characterised as an inefficient stretch-shortening cycle (Table 1)
The qualitative interpretation of the uncertainty associated with the effect (ES = 0.28, ±0.58) does lend support to the findings from previous experimental studies [1,34] that suggest jump height is somewhat insensitive to the braking centre of mass (COM) displacement utilised (Table 1)
Summary
Vertical jumping is a fundamental movement skill that develops during early childhood and is a key component of many sports. Since vertical jumping represents a whole-body movement, it can be purposively constrained in a variety of ways, namely, with and without a countermovement, arm swing or external loading [1]. The subsequent analysis of such testing is typically centred on the main performance variable, jump height, which can be reliably measured using a variety of affordable equipment. This somewhat simplistic approach may, on occasion, lack the required capacity to explain the changes observed [4,5] and rationalises, to some degree, the preponderance of force plate analysis within performance sport. In contrast to slight inter-individual differences that may exist in the shape of the unweighting phase [8], two radically different shapes have been consistently observed during the propulsion phase of the jump, a unimodal and a bimodal shape [9,10,11,12,13,14]
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