Asymmetry in a discrete concurrent task: is the two-legged countermovement jump asymmetric?

[Truncated abstract] To date, much of the previous research investigating movement asymmetry has focussed specifically on walking gait. However, as gait patterns and the CMJ significantly differ in the dynamic pattern, it is not known whether information regarding movement asymmetry obtained from gait studies can be applied to the CMJ. To this end five studies were conducted to explore the concept of asymmetry in bilateral concurrent action of the two-legged countermovement jump (CMJ) with an aim to enhance the knowledge and understanding of asymmetry observed in symmetrical actions. This study examined the various methods previously employed to quantify asymmetry in biomechanical data of various lower limb functions. Of the seven indices identified from the literature, three were excluded from the analysis as they did not specify the direction of the asymmetry. Strengths and weaknesses of the indices were assessed using both real and mock bilateral ground reaction force (GRF) data. The real data was the vertical GRF impulse during the push-off phase of the two-legged CMJ obtained from 10 physically active male participants. Comparison of the indices using the real data sets indicated that all of the indices were able to identify asymmetric performances (vertical impulse) and were sensitive enough to differentiate between participants with varying degree of asymmetry. The mock data was used to create different scenarios so strengths and weaknesses of each index could be identified. The results indicated that the Index of Asymmetry (IA) proposed by Vagenas and Hoshizaki (1991, 1992) was most suitable for the remaining series of studies. This study examined asymmetry in the vertical impulse during the two-legged CMJ, and its association with asymmetry in a one-legged CMJ and footedness. Fiftyeight (28 males & 30 females) participants performed 5 trials of the two-legged CMJ, 5 trials of the one-legged CMJ with the left limb and 5 trials of the one-legged CMJ with the right limb. Vertical impulse and jump height were derived from the vertical GRF data, collected from the left and right sides independently across all conditions. Footedness was assessed using the revised version of the Waterloo Footedness Questionnaire (WFQ-R). In the two-legged CMJ, 25 of the 58 participants (43%) generated greater impulse with the right limb, 11 (19%) with the left limb, and 22 participants (38%) demonstrated no consistent asymmetry in the impulse data. This was different to the one-legged CMJ where 10 participants (17%) generated greater impulse with the right limb, 17 (29%) with the left limb, and 31 (53%) demonstrated no significant difference in the impulse between the two limbs. While the cross-tabulation Chi-square indicated a significant association between asymmetry in the one-legged and two-legged CMJs (c2 [4] = 10.47, p <.05), the Goodman Kruskal’s Tau indicated that the strength of association was poor (t = 0.08, p = .07). The cross tabulation also revealed that impulse asymmetry during the two-legged CMJ was not related to footedness (c2 [4] = 1.96 p = .74 and c2 [4] = 6.54, p = .16, for the one-legged hop & WFQ-R, respectively...