Author(s): XU, W., CHENG, R.Q., ZHANG, Q.S., Institution: SHANGHAI UNIVERSITY OF SPORT, Country: CHINA, Abstract-ID: 1198

INTRODUCTION:
Countermovement jump (CMJ) is widely used to assess lower-limb neuromuscular function and stretch–shortening cycle (SSC) efficiency.(Philipp et al., 2023)However, CMJ outcomes are sensitive to verbal instructions, which may alter movement strategies and mechanical outputs, ultimately compromising test reliability. (Khuu et al., 2015) This study investigated the effects of varying verbal instructions (“Jump high” or “Jump fast” ) on the mechanical properties in elite pole vaulters.
METHODS:
Forty-one national pole vaulters (23 males, 18 females, status = ± cm, body mass = kg, age = years) performed three CMJs on a three-dimensional force platform (KWYP-FP6050, Kunwei; 1000 Hz). Athletes were randomly assigned to either a height-focused instruction (“Jump as high as possible”, High) or a speed-focused instruction (“Jump as fast as possible”, Fast). The CMJ mechanical properties (i.e., jump height [JH], ground contact time [GCT], braking phase duration [T Bra], propulsive phase duration [T Pro], countermovement depth [CMD], braking peak force [PF Bra], propulsive peak force [PF Pro], and modified reactive strength index [RSImod]) were calculated.
RESULTS:
Independent samples t-test indicates that the High condition produced greater JH (0.36 ± 0.07 m vs. 0.33 ± 0.06 m; p = 0.02, d = 0.42). The Fast condition significantly reduced GCT (0.59 ± 0.10 s vs. 0.68 ± 0.11 s; p < 0.001, d = 0.90), primarily due to shorter T Bra (0.13 ± 0.03 s vs. 0.16 ± 0.04 s; p < 0.001, d =0.9 ). PF Bra was greater in the Fast condition (1524.57 ± 345.39 N vs. 1273.03 ± 320.75 N; p < 0.001, d = 0.75), as was PF Pro(0.21±0.04 s vs. 0.24±0.04 s; p < 0.012，d =0.46). RSImod was also higher under the speed instruction (0.58 ± 0.14 vs. 0.54 ± 0.11; p = 0.05, d = 0.36).
CONCLUSION:
Different verbal instructions substantially modify CMJ biomechanics in pole vaulters. Height-focused instructions promote greater JH through prolonged force application, whereas speed-focused instructions increase PF Bra, reduce GCT, and enhance the RSImod. These findings demonstrate that CMJ outcomes are task-dependent and sensitive to verbal constraints. For performance monitoring in pole vaulting, speed-focused instructions may better reflect rapid force production and neuromuscular readiness, whereas height-focused instructions are more suitable for assessing maximal explosive capacity.