Author(s): FUJIBAYASHI, N., TOI, Y., SOGO, T., SOTA, N., Institution: CHUKYO UNIVERSITY, Country: JAPAN, Abstract-ID: 437

INTRODUCTION:
Brief vocalisation is commonly used as a coaching cue during explosive movements; however, its acute effects during stretch-shortening cycle actions remain unclear. This study aimed to examine whether a brief maximal vocalisation at initial ground contact enhances drop jump (DJ) performance and early-phase force development.
METHODS:
This study included 14 collegiate athletes who completed DJs at a height of 0.30 m under three randomised, within-subject conditions: Control (no vocalisation), Quiet-brace (silent abdominal bracing), and Vocal (brief maximal vocalisation at initial contact). Participants kept their hands on their hips throughout all trials. Contact time, jump height, and reactive strength index (RSI) were measured using an optical measurement system (Optojump Next, 1000 Hz). Vertical ground reaction force data were recorded at 1000 Hz using a 20 N contact threshold and low-pass filtered at 20 Hz. Average rate of force development (RFD) during the first 50 ms (RFD0-50) was calculated. Differences among conditions were assessed using one-way repeated-measures ANOVA with Holm-adjusted pairwise comparisons. Pearson correlation analysis was used to examine the association between changes from Control to Vocal in RSI and RFD0-50.
RESULTS:
RSI differed significantly among conditions (p=0.00013) and was higher in Vocal (2.13 +/- 0.52) than in Control (1.89 +/- 0.48; p=0.0041, dz=1.03) and Quiet-brace (1.80 +/- 0.53; p=0.00019, dz=1.55). Additionally, contact time differed across conditions (p=0.0061) and was shorter in Vocal (0.179 +/- 0.030 s) than Quiet-brace (0.198 +/- 0.037 s; p=0.0090). Jump height exhibited no significant difference among conditions (p=0.068) but tended to be higher in Vocal (36.7 +/- 5.2 cm) than Control (34.6 +/- 5.4 cm). RFD0-50 was greater in Vocal (86.7 +/- 17.3 kN/s) than in Control (73.5 +/- 19.5 kN/s; p=0.0062, dz=1.03) and Quiet-brace (71.9 +/- 21.0 kN/s; p=0.014, dz=0.85). Changes in RSI and RFD0-50 from Control to Vocal conditions were strongly correlated (r=0.82, p=0.00035).
CONCLUSION:
A brief maximal vocalisation at initial ground contact acutely enhanced DJ performance, as evidenced by increased RSI and reduced contact time, and was accompanied by greater early-phase force development. These findings suggest that enhanced rapid force production may partially explain the RSI improvement when using vocalisation as a cue.