Author(s): LAI, M., MAK, M.C.W., HO, I.M.K., LUK, J.T.C., Institution: TECHNOLOGICAL AND HIGHER EDUCATION INSTITUTE OF HONG KONG (THEI), Country: HONG KONG, Abstract-ID: 315

INTRODUCTION:
The external attentional focus of attention (e.g, focusing on the rungs of the Vertec to be reached) has been shown to increase jump height by promoting greater forces. However, the current studies primarily targeted bilateral jump performance, and these findings may not necessarily be applicable to unilateral activities. Moreover, the presence of larger inter-limb asymmetry (IA) in single-leg countermovement jumps (SLCMJ) is often linked to decreased sports performance and a higher risk of injury, suggesting the high importance of observing SLCMJ asymmetry.  This study investigated the impact of the external focus cue ("reaching for the ceiling") on jump height (JH) and time to take-off (TTT) during SLCMJ in recreationally active young adults, as well as the IA changes. The findings can inform better coaching language to enhance training effects for the SLCMJ exercise with executions directed to external attentional focus. 
METHODS:
Twenty-six healthy participants, aged between 18 and 35 years old, performed multiple akimbo SLCMJs on each leg under two randomised conditions: 1) Control (no cue used) and 2) external cue (head reach for the ceiling). JH and TTT were measured using Hawkin Dynamics wireless dual force plates. Asymmetries were calculated using the Standard Percentage Difference formula. Paired t-tests, effect sizes (Hedges’ g), and intraclass correlation coefficients were computed to compare performance changes. 
RESULTS:
ICC values indicated excellent reliability for JH (0.900–0.901) and good-to-excellent reliability for TTT (0.857–0.888). External cueing significantly improved JH for both legs (effect sizes: left leg g = 0.671, p = 0.002; right leg g = 1.082, p = 0.049). JH asymmetry showed a minimal, non-significant reduction from 10.60% to 9.44% (p > 0.05).  Individual-leg TTT increased significantly (left leg: g = 0.237, p = 0.016; right leg: g = 0.280, p = 0.03), despite non-significant changes in TTT asymmetry (p > 0.05).  
CONCLUSION:
Adding external cues when performing unilateral CMJ can increase jump height and time to take-off but it cannot induce significant changes in JH and TTT asymmetry. Therefore, the external attentional focus can be used to maximise unilateral CMJ height during plyometric tasks, but it is not effective in lowering IAs for injury prevention purpose. To further explore the use of external cues for IA reduction, future studies may include the condition of applying the external cue only to the weaker limb. Since the use of external attentional focus can boost the SLCMJ performance, it is speculated that the “asymmetric” application of external focus on the weaker side may potentially minimise the IA.