Sleep Quality, Insomnia Symptoms, and Perceived Fatigue in Relation to Countermovement Jump Performance Across Repeated Trials in Resistance-Trained Adults.

Objectives: This study examined the associations of habitual sleep quality, insomnia symptoms, and perceived fatigue with countermovement jump (CMJ) performance across repeated trials in resistance-trained adults. Methods: A total of 118 resistance-trained adults (90 men and 28 women) completed the Pittsburgh Sleep Quality Index (PSQI), Insomnia Severity Index (ISI), and Fatigue Severity Scale (FSS). Participants performed six maximal CMJ trials at 0, 2, 4, 6, 8, and 10 min. Mean and best CMJ height, within-participant coefficient of variation, first-to-last change, and individual performance slope were calculated. Linear mixed-effects models and adjusted regression analyses were applied. Results: PSQI was not associated with mean CMJ height, best CMJ height, or within-participant variability (all p > 0.05). However, a significant PSQI × time interaction was observed (B = -0.061 cm/min per 1-SD higher PSQI, 95% CI -0.099 to -0.023; p = 0.002; q = 0.005), indicating that poorer sleep quality was associated with a smaller increase in CMJ height across repeated trials. Exploratory participant-level analyses derived from the same six CMJ measurements showed associations in the same direction for first-to-last change and individual CMJ slope. These associations remained significant after correction within the six trajectory-focused analyses but not after correction across all 18 participant-level regressions. ISI and FSS were not associated with CMJ trajectory or variability (all p > 0.05). Conclusions: Poorer habitual sleep quality was not associated with maximal or average CMJ performance, but was related to an attenuated improvement across repeated maximal CMJ trials. The observed association was small, and its practical significance remains uncertain. The within-session CMJ trajectory should therefore be considered exploratory rather than a validated indicator of recovery or neuromuscular readiness.